Title Author(S)

th 5 European Conference on Severe Storms 12 - 16 October 2009 - Landshut - GERMANY

ECSS 2009 Abstracts by session

ECSS 2009 - 5th European Conference on Severe Storms 12-16 October 2009 - Landshut – GERMANY List of the abstract accepted for presentation at the conference: O – Oral presentation P – Poster presentation

Session 09: Severe storm case studies and field campaigns, e.g. COPS, THORPEX, VORTEX2

Page Type Abstract Title Author(s)

An F3 downburst in Austria - a case study with special G. Pistotnik, A. M. Holzer, R. 265 O focus on the importance of real-time site surveys Kaltenböck, S. Tschannett J. Bech, N. Pineda, M. Aran, J. An observational analysis of a tornadic severe weather 267 O Amaro, M. Gayà, J. Arús, J. event Montanyà, O. van der Velde Case study: Extensive wind damage across Slovenia on July M. Korosec, J. Cedilnik 269 O 13th, 2008 Observed transition from an elevated mesoscale convective J. Marsham, S. Trier, T. 271 O system to a surface based squall line: 13th June, Weckwerth, J. Wilson, A. Blyth IHOP_2002 08/08/08: classification and simulation challenge of the A. Pucillo, A. Manzato 273 O FVG olympic storm H. Bluestein, D. Burgess, D. VORTEX2: The Second Verification of the Origins of Dowell, P. Markowski, E. 275 O Rotation in Tornadoes Experiment Rasmussen, Y. Richardson, L. Wicker, J. Wurman Observations of the initiation and development of severe A. Blyth, K. Browning, J. O convective storms during CSIP Marsham, P. Clark, L. Bennett The development of tornadic storms near a surface warm P. Groenemeijer, U. Corsmeier, 277 O front in central England during the Convective Storm C. Kottmeier Initiation Project (CSIP) Impact of Dryline Misocyclones on Convection Initiation on Y. Richardson, C. L. Ziegler, M. 279 O 19 June 2002 during IHOP Buban, J. Marquis, J. Wurman A. Dörnbrack, G. Craig, S. Jones, O T-NAWDEX - Basic Research allied to the future of NWP H. Wernli P Analysis of multicell storm development on 22 May 2007 N. Pavlovic Berdon 281 P The Balkan cyclone M. Stojanovic Storm-scale radar observations of supercells observed M. I. Biggerstaff, C. Ziegler, D. P during VORTEX2 Betten, T. Thompson, D. Burgess The January 2009 precipitation extremes over Calabria F. Fusto P region, Southern Italy Severe Winter Storms over the Western and Central State of A. M. Gomes, G. Held 283 P São Paulo, Brazil HARE – A new intelligent hail recorder for networks and M. Löffler-Mang 285 P field campaigns

263 Page Type Abstract Title Author(s)

M. Parker, A. French, C. Mobile sounding measurements of the near storm 287 P Letkewicz, M. Morin, K. environment during VORTEX2 Rojowsky, D. Stark, G. H. Bryan Y. Richardson, P. Markowski, J. 289 P Mobile mesonet observations in VORTEX2 Wurman, K. Kosiba K. Kosiba, J. Wurman, Y. P Mesocyclone-scale mobile radar observations in VORTEX2 Richardson, P. Markowski Thunder Activity With Heavy Rain Over Egypt In Early P F. M. El Ashmawy, A. L. Essawy Spring J. Egaña, S. Gaztelumendi, D. Convective storms over Basque Country: June 2008 cases 291 P Pierna, I. R. Gelpi, K. Otxoa de study Alda Study of microphysical and thermodynamic structures K. Friedrich, R. Humphrey, J. P within supercell thunderstorms Wurman, K. Kosiba H. Y. Inoue, K. Kusunoki, W. High resolution X-band Doppler radar observation of 293 P Mashiko, S. Hayashi, H. misocyclones along the convergence line Yamauchi Very strong convection at the Baltic coast of Lithuania on 295 P I. Marcinoniene 25 November 2008 K. Kusunoki, H. Inoue, W. Mashiko, S. Hayashi, W. Kato, K. Wind gust and storm evolutions observed during the Shonai 297 P Araki, K. Bessho, S. Hoshino, M. Area Railroad Weather Project: A preliminary survey Nakazato, T. Imai, Y. Hono, T. Takemi, T. Fukuhara, T. Shibata A case study of severe convection over Central Europe with D. Plačko-Vrsnac, N. Strelec- 299 P a detailed analysis of development over Croatia on 22 nd Mahovic and 23 rd June 2007 T. Púčik, M. Francová, D. Rýva, 301 P Derecho on the 25th June 2008 M. Kolář Case study of severe windstorm over Slovakia and Hungary A. Simon, J. Kanák, A. Sokol, M. 303 P on 25 June 2008 Putsay, L. Uhrínová, K. Csirmaz N. Strelec-Mahovic, D. Plačko- P Snowstorm in southern Croatia, 18 February 2009 Vrsnac Examination of two severe thunderstorm events in southern 305 P H. Tuschy, M. Hagen, G. J. Mayr Germany Comparison of detailed model results of MCS with radar B. White, A. Blyth, J. Marsham, P observations during CSIP K. Browning

264 5h European Conference on Severe Storms 12 - 16 October 2009 - Landshut - GERMANY

AN F3 DOWNBURST IN AUSTRIA – A CASE STUDY WITH SPECIAL FOCUS ON THE IMPORTANCE OF REAL-TIME SITE SURVEYS Georg Pistotnik1, Alois Martin Holzer2, Rudolf Kaltenböck3, Simon Tschannett4

1Central Institute for Meteorology and Geodynamics, Austria, [email protected] 2European Severe Storms Laboratory e.V., Germany, [email protected] 3Austrocontrol, Aeronautical Meteorological Service, Austria, [email protected] 4Weatherpark GmbH, Meteorological Research and Services, Austria, [email protected]

(Dated: 15 September 2009)

I. INTRODUCTION On March 1st of 2008, the powerful late winter cyclone “Emma” caused widespread damage over Central Europe. Embedded in the synoptic-scale storm field, deep convection along the cold front resulted in a significant enhancement of gusts in some places, peaking in an unusually strong downburst in a sparsely populated area near Braunau (Austria). Only a site survey revealed the extraordinary intensity of this downburst that vividly contrasted with its sparse media coverage. This study aims to elaborate how the assessment of this case would have taken a significantly different outcome without the accomplishment of this site survey. FIG. 1: MSG RGB “airmass product” image at 08:00 UTC on st II. PRESENTATION OF RESEARCH March 1 of 2008, and detected lightning within the last hour (Schipper et al., 2008). Cyclone “Emma” formed near Newfoundland and travelled eastward over the Northern Atlantic Ocean on the last days of February 2008, where it encountered an increasingly favourable environment for intensification until it reached its minimum central pressure and its maximum strength over Southern Scandinavia on March 1st. As its cold front raced south-eastward over the Netherlands and Germany in the morning hours of this day, it was overrun by a dry intrusion, a process well-known to favour the formation of a convective line along the cold front as it creates potential instability which is ready to be released by the forced ascent of cyclonic vorticity advection (CVA). Extremely dry stratospheric air is visible by the purple colour in the Meteosat “airmass product” image at 08 UTC in Fig. 1. The arrival of this dry intrusion and the superimposed forced ascent of a strong CVA maximum caused the cold front to obtain a “split front” character (Schipper et al., 2008), with a dissolving high cloud shield and incipient cooling of the upper troposphere ahead of the FIG. 2: “INCA” temperature analysis (Haiden et al., 2009) at 10:00 st surface cold front which is hence marked by an intensifying UTC, March 1 of 2008, when the cold front has just entered convective line, showing an unusual high amount of Northern Austria. Location of Braunau is denoted by the black “x”. lightning as it moved over Germany towards the Czech Republic and Austria. Evaporative cooling caused by the The circumstances enabling the formation of this falling precipitation encountering dry environmental air extraordinary local storm can be regarded as a coincidence provoked the formation of a strong cold pool immediately of supporting factors over a wide range of scales, from the behind the surface front (Fig. 2), further increasing the synoptic scale (i.e., the presence of a strong frontal zone) via temperature and pressure gradient and thus accelerating the the mesoscale (i.e., the interaction between the dry intrusion propagation of the convective line that was accompanied by and the cold front) to small scales, whose processes severe wind gusts in many places. The series of downbursts determined the final position and strength of this downburst finally culminated in the Braunau event at 09:46 UTC. event while remaining mostly concealed even to the most alert meteorologist’s eye. The authors of this study encountered a similar scale-cascade while moving their

265 5h European Conference on Severe Storms 12 - 16 October 2009 - Landshut - GERMANY attention from the confusing and widespread synoptic-scale revealed that the damage extent in the core of this downburst storm damages via mesoscale areas of even more reached T5 and locally even T6 intensity (Hubrig, 2004), pronounced downburst signs to the remote but incredible corresponding to upper F2 and locally lower F3 intensity on marks of this “king storm” near Braunau, strikingly closing the Fujita scale (Fig. 3). Thus, even the most conservative the circle between storm synthesis and storm analysis. valuation of the involved wind speed yields maximum gusts The accomplishment of the site survey was not only of at least 200 km/h, turning this event into the strongest based on meteorological ambition and supportive downburst ever documented in Austria (Fig. 4). arrangements but also on (too much of) chances and luck: if this downburst had not hit and severely damaged the III. RESULTS AND CONCLUSIONS infrastructure of a large electricity supplier, the means and Embedded in the synoptic-scale storm field of the powerful ways to perform a thorough site survey would never have late winter cyclone “Emma”, an F3 downburst occurred near unfolded, leaving this case rather buried in oblivion than Braunau (Austria) on March 1st of 2008. Only a thorough finding its way into scientific literature. site survey revealed the nature, the whole extent and extraordinary intensity of this event that received little attention in the media as it affected a sparsely populated area and was dwarfed by superficially more spectacular damage events occurring within cities, disrupting major traffic routes and / or causing injuries and even fatalities. However, as this downburst by mischance severely damaged the infrastructure of a large electricity supplier, its aftermath turned out to be far-reaching in a more subtle way, by not only evoking the scientific interest in a downburst event close to the very peak of its known probability distribution, but also showing the vulnerability of power supply and other implicitnesses of modern life. Thus, this case has proven valuable in further raising the awareness of extreme (convective) storms in the meteorological community as well as in risk management circles, by providing a reference “worst-case scenario” for both points of view. This presentation aims to be not only a case study of a severe weather event but also a plea for the importance of near real-time site surveys to capture the dimensions of a (convective) storm event and properly classify it. Hopefully, this storm event will turn out to be another small but important step on the path towards a more systematic investigation of severe weather events.

IV. ACKNOWLEDGEMENTS The authors would like to thank all the people who generously provided the framework requirements of a successful site survey in the Braunau region, including the FIG. 3: Examples of the storm damage as seen from the helicopter (top) and at the surface (bottom). officials of the municipality of St. Peter am Hart and others who do not like to be mentioned by name. Thanks are also adressed to Martin Hubrig and Greg Stumpf (NOAA/NSSL) for helping in the assessment of the damages and to Martin Auer and Jarno Schipper (both ZAMG) for the unbureaucratic provision of satellite data.

V. REFERENCES Haiden, T., Kann, A., Pistotnik, G., Stadlbacher, K., and Wittmann, C.: Integrated Nowcasting through Comprehensive Analysis (INCA) – system documentation. (http://www.zamg.ac.at/fix/INCA_system.pdf). Schipper, J., Groenland, R., and Jacobs W.: Passage of FIG. 4: Damage map of the affected area; colour shades represent the damage extent according to the T-scale. The legend bar in the intense cold front / convective line over Europe, 29 lower left shows a distance of 2 kilometres. The red circle (above February to 01 March 2008. EUMeTrain case study. legend bar) denotes the automatic station of Ranshofen that was Hubrig, M., 2004: Analyse von Tornado- und Downburst- closely missed by the downburst and recorded a maximum gust of Windschäden an Bäumen (Analysis of Tornado and only 104 km/h. Downburst Wind Damage to Trees). Forst und Holz, 59, 78-84. The deeper the investigations got, the higher the estimations of the damage had to be raised. Two days’ systematic field mapping, photographic documentation, interviews with eye-witnesses and a helicopter flight finally

266 5h European Conference on Severe Storms 12 - 16 October 2009 - Landshut - GERMANY

AN OBSERVATIONAL DESCRIPTION OF A TORNADIC SEVERE WEATHER EVENT J Bech1, N Pineda1, M Aran1, J Amaro1, M Gayà2, J Arús3, J Montanyà4, O van der Velde4

1Servei Meteorològic de Catalunya, Berlin 38-46, Barcelona 08029, Catalonia, Spain ([email protected]) 2Agencia Estatal de Meteorologia, DT Illes Balears, Palma de Mallorca, Illes Balears, Spain 3Agencia Estatal de Meteorologia, DT Catalunya, Barcelona, Catalonia, Spain 4Electrical Engineering Dep., Technological University of Catalonia, Terrassa, Spain (Dated: 15 September 2009)

I. INTRODUCTION weather took place. The cold core at 500 hPa was about – This study presents an analysis of a severe weather 25ºC at 00 UTC (–17ºC over Barcelona). case study that took place during the early morning of the 2nd of November 2008, when intense convective activity associated to a rapidly evolving low pressure system affected the southern coast of Catalonia (NE Spain). The synoptic framework was dominated by an extended upper level trough and an associated surface frontal system extending from Southern Spain along the Mediterranean coast of the Iberian Peninsula to SE France, which moved north-eastward. A low pressure area in the eastern coast of the Iberian Peninsula intensified from 00 to 06 UTC (Fig. 1). South-easterly winds in the north of the Balearic Islands and the coast of Catalonia favoured high values of 0-3 km storm relative helicity (about 300 m2s-2) which combined with moderate MLCAPE values (750-1000 J kg-1) and high shear favoured the conditions for organized convection.

FIG. 2: 2nd November 2008 00 UTC MSG satellite water vapour image (6.2 μm) showing the convective development area in the eastern part of the Iberian Peninsula.

Between 00 and 06 UTC sea level pressure dropped about 7 hPa in the southern part of Catalonia and even more in the west of Catalonia, reaching 11.7 hPa (Raimat station), which is a value associated to rapid cyclogenesis development according to Carlson (1991). Moreover, other typical characteristics of these systems present in this case are: a). the appeareance of the low pressure system at the polar sector of a jet (in this case over Marocco pointing towards the Balearic Islands at 00 UTC); b). a strong thermal boundary, which is clearly appreciated in the analysis performed using the LAPS system (Albers et al 1996) over Catalonia (not shown here).

II. RADAR DATA AND DAMAGE SURVEY A number of multicell storms coming from the FIG. 1: UKMO sea level pressure and frontal analysis on 2nd Mediterranean -and at least one supercell, as indicated by November 2008 00 UTC showing the low pressure area over the eastern Mediterranean coast of the Iberian Peninsula. weather radar observations- clustered later in a mesoscale convective system and moved north-easterly across MSG satellite images show an area of vigorous Catalonia, producing ground-level strong damaging wind convective cloud development in the eastern coast of Spain, gusts, a tornado –which caused F2 damage– and heavy favoured by the surface low pressure development, the upper rainfall. Two thunderstorms (Fig. 3) were particularly active level trough and the presence of associated series of jets: J1, and most damage observed on ground was later associated to J2, J3 (as depicted in Fig. 2); J1 was about 120 kts, and J2 – them. which triggered convection via potential instability at mid Total lightning activity (intra-cloud and cloud to and high levels– about 105 kts while J3 was 60 kts. Satellite ground flashes) was also relevant, exhibiting several images indicate the presence of several vorticity centres classical features such as a sudden increased rate before (marked as red encircled Xs in Fig.2). One of them moved ground level severe damage, as discussed in a companion along J2 over the coast of Catalonia, where the severe study (Pineda et al. 2009). Remarkable surface observations of this event include 24 h accumulations exceeding 100 mm

267 5h European Conference on Severe Storms 12 - 16 October 2009 - Landshut - GERMANY in three different observatories and 30 minute rainfall amounts of 40 mm which caused local flash floods. As the system evolved northward later that day it also affected SE France causing large hail, ground level damaging wind gusts and heavy rainfall.

FIG. 3: Radar reflectivity 1 km CAPPI 1:42 UTC composite showing the two storms (about 41N) approaching the southern coast of Catalonia (scale in dBZ). FIG. 5: Depiction of the damage survey performed over the Miralcamp village, affected by F2 damage. Four towers of high voltage power lines (NW of the picture) were knocked down during the event.

III. RESULTS AND CONCLUSIONS Similarly as in the study of Bech et al. (2007) the passage of the thunderstorms in the proximity of a radar allowed recording clear signs of radial shear and signs of rotation (Fig. 4), which in other circumstances would have been undetected. In some cases they could be associated to the convective cells that caused strong surface winds and substantial damage by comparing the locations of the survey (as in Fig. 5) with radar data, which helped clarifying the tornadic origin of the damage in a case where no visual evidence of a tornado was available, as in the case of the Castellcir tornado (Aran et al. 2009, Bech et al. 2009).

IV. REFERENCES Albers S., McGinley J., Birkenheuer D., Smart J., 1996: The

Local Analysis and Prediction System (LAPS): Analyses of clouds, precipitation, and temperature. Weather Forecast. 11 273-287. Aran M., Amaro J., Arús J., Bech J., Figuerola F., Gayà M., Vilaclara E., 2009: Synoptic and mesoscale diagnosis of a tornado event in Castellcir, Catalonia, on 18th October 2006. Atmos. Res. 93 147-160. Bech J., Gayà M., Aran M., Figuerola F., Amaro J., Arús J., 2009: Tornado damage analysis of a forest area using site survey observations, radar data and a simple analytical vortex model. Atmos. Res. 93 118-130. Bech J., Pascual R., Rigo T., Pineda N., López J. M., Arús J., Gayà M., 2007: An observational study of the 7 September 2005 Barcelona tornado outbreak. Nat. Hazards Earth Syst. Sci., 7 129-139. Carlson T. N., 1991: Mid-latitude Weather Systems. Routledge. 482 pp. Pineda N., Bech J., Rigo T., Montanya J., van der Velde O., 2009: Total lightning analysis of a tornadic severe

FIG. 4: LMI 0.6º PPIs showing reflectivity (in dBZ) and Doppler weather event. Proc. European Conference on Severe radial velocity fields (in m/s) at 3:18 UTC, when the F2 tornado Storms 2009 (this issue). associated to the northernmost cell (about 40 km NE from the radar) took place.

268 5th European Conference on Severe Storms 12 - 16 October 2009 - Landshut - GERMANY

CASE STUDY: EXTENSIVE WIND DAMAGE ACROSS SLOVENIA ON JULY 13 TH, 2008 Marko Korošec1, Jure Cedilnik2

1University of Ljubljana, Faculty for Mathematics and Physics, Jadranska 19, SI-1000 Ljubljana, Slovenia, [email protected] 2 Slovenian Meteorological Service, Environmental Agency of Slovenia, Vojkova 1b, SI-1000 Ljubljana, Slovenia, [email protected]

(Dated: 15 September 2009)

I. INTRODUCTION m/s gusts, though it is estimated that the microbursts' speed During the mid afternoon of July 13th 2008 parts of was likely exceeding 120 km/h in the places where the Slovenia experienced severe weather due to extreme damage was the greatest. The damage along the path was convective outburst. Most of the damage was caused by hail mostly caused by strong downbursts (large areas of uprooted and strong winds and was connected to one single supercell trees, roofs lifted off from houses) and in the eastern part crossing the country by the longest diagonal. large hail, see Figure 2 for areas wind reported wind This case study illustrates the general situation, damage. There are some indicators that near the village of presents some remote-sensing material and gives some Gozd (circled area in Figure 2), a tornado may have occured arguments for an unconfirmed, though possible tornado (large and heavy debris flown in unusual – also cyclonic occurrence. -directions). However, large areas of uprooted trees in the nearby woods clearly indicate unidirectional damage and the microbursts' direction was also significantly perturbed by the II. PRESENTATION OF RESEARCH hilly terrain. Therefore the occurrence of tornado is A very pronounced upper air through rapidly officially not confirmed by the national meteorological moving eastwards and a very warm and moist southerly service. A detailed analysis on a Doppler radar (situated winds in lowest layers of the atmosphere were the two key roughly 40 km away) workstation also showed no evidence parameters of the general weather situation. of the mesocylcone and also only a weak WER signal in the There was some convective activity present in the supercell. morning hours, yet the relevant action began with a strong convective cell formation at around noon local time (10 UTC) over the Nrothern Adriatic sea. The storm then moved northeastwards, its severity increased and it also showed some signs of movement to the right. The storm path is shown in Figure 1. Besides radar imagery, strong convection is observed also in numerous satellite images' combinations and with lightning detectors.

FIG. 2: Wind damage reports on July 13th (red dots). The magenta circle presents the area with a possible tornado occurence.

IV. REFERENCES Environmental Agency of Republic of Slovenia, National meteorological service, "Poročilo o vremenskem dogajanju ob nevihtnih neurjih v nedeljo in ponedeljek, 13. in 14.7.2008", Report on extreme weather event (in Slovenian) http://www.arso.gov.si/vreme/poročila_in_projekti/neurja FIG. 1: Radar images (Zmax) at different times, shown only for the _20080713-14.pdf relevant supercell. Bunting, William F., B. E. Smith: A guide for conducting III. RESULTS AND CONCLUSIONS convective windstrom surveys, NOAA Technical memorandum NWS SR-146, Scientific Services Most of the damage was caused in the second part of Division,Southern Region, Fort Worth, Texax, Feb. 1993 the track, where the storm had more pronounced supercell attributes. The highest measured wind speeds were up to 23

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270 5th European Conference on Severe Storms 12 - 16 October 2009 - Landshut - GERMANY

OBSERVED TRANSITION FROM AN ELEVATED MESOSCALE CONVECTIVE SYSTEM TO A SURFACE BASED SQUALL LINE: 13TH JUNE, IHOP_2002 JH Marsham1, SB Trier2, TM Weckwerth2, JW Wilson2, AM Blyth1

1National Centre for Atmospheric Science (NCAS), School of Earth and Environment, University of Leeds., Leeds, LS2 9JT, UK. [email protected] 2National Center for Atmospheric Research (NCAR), Boulder, Colorado, USA (15 September 2009)

I. INTRODUCTION Nocturnal deep convection is often associated with severe weather but its prediction remains a difficult forecasting problem. Such convection often has its source air elevated above the planetary boundary layer. Elevated convection forms an important part of the diurnal cycle in the mid-west of the USA, where a nocturnal maximum in convection is observed. For the 2002 International H20 Project (IHOP_2002) the nocturnal maximum was shown to result from locally initiated storms, which generally formed from elevated initiation episodes, rather than just storms that were initiated elsewhere during the day propagating into the IHOP area at night (Wilson and Roberts, 2006). Systems that formed from elevated initiation episodes were shown to be less likely to produce a significant gust front than systems formed from surface-based initiation episodes, but tended to be longer lived if they produced such a gust front (Wilson and Roberts, 2006). An IHOP_2002 case study of an elevated initiation episode that led to a surface-based MCS with a substantial gust front is discussed below.

II. OUTLINE OF THE SYSTEM EVOLUTION The system formed from four initiation episodes that occurred between 0500 and 1000 UTC (2300 to 0400 LT), close to the Oklahoma panhandle, ahead of a southwest- northeast oriented cold front. By 1125 UTC these had led to the northwest-southeast oriented lines of deep convection shown in Figure 1(a). These lines gradually developed to give a southwest-northeast oriented squall-line structure (Figure 1b). This occurred by approximately 1300 UTC in western Oklahoma and 1600 UTC in eastern Oklahoma.

III. RESULTS AND CONCLUSIONS Radiosondes close to the initiation episodes (for example Figure 2) showed elevated layers of air with high theta-e, located above a stable nocturnal boundary layer. The storms initiated from these layers. The best observed initiation episode occurred close to the SPol radar that was deployed for IHOP_2002. This FIG. 1: Radar composite of reflectivity from low-level PPI (plan showed that the initiation was a result of the position indicator) scans at (a) 1125 and (b) 1605UTC. Low-level intersection of a northwest-southeast oriented winds from surface observations are shown in white. White lines convergence line with a wave propagating through the show state boundaries, with Oklahoma in the centre. low-level stable air (Figure 3). The stable air with near have been studied (not shown). During the day, once neutrally stratified air above (Figure 2), together with the boundary layer had warmed, the effect of the cold a southerly low-level jet favours the trapping of wave pool was fairly uniform, showing the pressure energy at low-levels in this case (Crook, 1988). increase, rapid cooling, wind-speed increase and water Using a combination of surface observations vapour mixing ration (WVMR) decrease expected and radar data the evolution of the properties of the from the observed squall-line MCS. During the night, cold pool as the system propagated across Oklahoma

271 5th European Conference on Severe Storms 12 - 16 October 2009 - Landshut - GERMANY the cold pool effects were more spatially variable, IV. AKNOWLEDGMENTS showing a pressure increase, a rapid cooling, a wind- John Marsham would like to thank the British Council speed increase and a decrease in WVMR in the west Researcher Exchange Programme for funding his visit to and a much smaller cooling and wind-speed increase NCAR and Tammy Weckwerth and Jim Wilson for hosting in the east, together with an increase in WVMR. In it. In addition we would like to thank all those who contributed to the IHOP_2002 field campaign. particular, at night some mesonet stations experienced V. REFERENCES precipitation and a pressure rise for at least an hour Bryan GH, Rotunno R, Fritsch JM, 2007. Roll circulations before any cold downdraught air could penetrate the in the convective region of a simulated squall line. J. stable nocturnal boundary layer. Early on in the Atmos. Sci., 64, 1249-1266. systems evolution, when downdraughts from the Crook NA, 1988. Trapping of low-level internal gravity convection interacted with the stable nocturnal waves, J. Atmos. Sci., 45, 1533-1541. boundary layer, bores and waves were observed Parker MD, 2008. Response of simulated squall ines to low- propagating ahead of the cold pool and initiating level cooling. J. Atmos. Sci., 65, 1323-1341. further deep convection. Wilson JW and Roberts RD, 2006. Summary of convective The reorientation of the northwest-southeast storm initiation and evolution during IHOP: Mon. Weather oriented lines of convection (Figure 1a) to the Observational and modelling perspective. Rev., 134, 23-47. southwest-northeast squall line (Figure 1b) happened before any significant surface heating in western Oklahoma (1300 UTC), and later after some surface warming in the east (1600 UTC). A combination of surface mesonet and radar data suggests that in both the west and the east the time of the reorientation of the convection was similar to the time when the surface cold pool generated by the system could first lift surface air to its level of free convection (essentially the reverse of the surface-based to elevated transition modelled by Parker, 2008). Particularly in the east, across-squall-line banding was observed at the time of the transition (e.g. Figure 1b) similar to that described by Bryan et al (2007). The case-study raises a number of interesting questions concerning the sensitivity of the cold-pool outflow to microphysical processes and the stable nocturnal boundary layer, and the sensitivity of the transition from elevated to surface-based to the cold- pool outflow. These are being investigated using the Weather Research and Forecasting (WRF) model.

FIG. 2: ARM radiosonde profile from Vici at 0829 UTC, close to the initiation episode observed using the SPol radar (Figure 3). FIG. 3: (a) SPol 1.2 degree scan reflectivity and (b) Doppler winds, both at 0911 UTC. The wave is seen most clearly in (a) approximately 100 km southeast of SPol (see arrow). The convergence line is seen most clearly in (b), running nothwest to southeast. (c) A virtual reflectivity cross-section (built up from multiple PPIs) from SPol southeastwards through the wave at 0911 UTC (approximately along the yellow arrow).

272 5th European Conference on Severe Storms 12 - 16 October 2009 - Landshut - GERMANY

08/08/08: CLASSIFICATION AND SIMULATION CHALLENGE OF THE FRIULI VENEZIA GIULIA OLYMPIC STORM Arturo Pucillo1, Agostino Manzato1

1OSMER – Osservatorio Meteorologico Regionale dell' ARPA Friuli Venezia Giulia, Via Oberdan 18, 33040 Visco (UD), Italy, [email protected] (Dated: 14 September 2009)

I. INTRODUCTION An unusually severe storm hit the Friuli Venezia Giulia region (hereafter FVG), northeastern Italy, in the late evening of the 8th August 2008. Noticeable damages (and two casualties) resulted from this storm, in particular in the town Grado, in prevalence due to very strong gusting winds (up to 45.3 m/s). This work aims to classify the event in terms of a recognizable mesoscale structure through the analysis of a mesonetwork of about 30 stations measuring 5 minutes meteorological data, the OSMER-ARPA Fossalon C-band Doppler radar data, the Udine-Campoformido radiosounding data and the Eumetsat MSG images. Moreover numerical simulations have been provided by different LAMs (WRF, ALADIN, MOLOCH), whose outputs have been compared in order to find out limits and good forecasting performances and to better understand the synoptic and mesoscale patterns which triggered this event.

II. DESCRIPTION The uncertainty in the definition of the event immediately arose because of the contemporary presence of linear-wind compatible land damages and observed funnels and FIG. 1: VMI (dBZ) and stations data during the “bow echo” stage of waterspouts over an area 15 to 20 km to the east of Grado, the storm over FVG plain at 21:35 UTC. that could push the classification towards a tornadic supercell as done by media reports. Nevertheless, the results Some considerations about winds and equivalent of the analysis highlight that the storm structure has many potential temperature behavior on different stations (over the elements in common with “bow echo” convective system alpine ridge and in the vicinity of the most damaged area scheme, which includes mesovortex dynamics that can lead along the coast) and about Doppler Radar signature follow to water- and land-spout occurrence conditions other than the mesoscale analysis. In particular, a simple Bernoulli- strong linear winds (Wakimoto et al., 2006). The role of the based model has been applied to check the role of the strong gusting winds observed has been broadened after the convective process on the magnification factor between consideration that a density current sloping downhill the 1500m ASL wind value registered on Pala d'Altei and Alps could act as a high momentum - high static stability coastal meteorological stations (Lignano, Grado and Boa flow injected inside a thunderstorm. It can generate a strong Paloma). Moreover, the Doppler signature shows tracks of low level outflow by vertical momentum transfer and mesovortexes along the leading path of the convective line, negative buoyancy acceleration (the well known “rear then destroyed by the strong outflow corresponding to the inflow jet”, see Atkins and St. Laurent, 2009 and reference maximum gusting winds, according to the cold-pool shear therein). A typical northwestern short wave with a cold front balance theory (Rotunno et al., 1988). Some theoretical passing over the Alps, preceeded by warm and moist considerations about the role of the density current southwestern winds aloft over a potentially unstable low associated to the cold front acting as Rear Inflow Jet in the troposphere, triggered deep moist convection after an intense convective system have been considered. 300 hPa wind jet streak divergence, often turning into The second part of the work collects 5 different supercellular storms characterized by large hailstones simulations performed by 3 high resolution LAMs: WRF (diameter up to 5 cm). The advection of cold and dry air, (two different versions initialized by GFS and ECMWF), delayed by the presence of the alpine orographic barreer, ALADIN (initialized by ARPEGE) and MOLOCH resulted in a sudden increase in low level northwestern wind (initialized by ECMWF). Performances seem quit poor as that feeded a preexisting convective cell at the bottom of the for the intensity of the winds (the real discriminant factor) Alps, over Veneto and FVG plains, driving to a bow echo while the general synoptic and mesoscale pattern have been shaped VMI track associated to damaging winds along the properly captured by all the models. In addition, all models gust front of the system (Fig. 1). are not able to show the well-developed pre-frontal convection, whose role seems to be important in such an occurrence.

273 5th European Conference on Severe Storms 12 - 16 October 2009 - Landshut - GERMANY

Atkins N. T., St.Laurent M., 2009: Bow Echo Mesovortices. Part II: Their Genesis. Mon.Wea.Rev., 137, 1514-1532. Rotunno R., Klemp J.B., Weisman M.L., 1988: A Theory for Strong, Long-Lived Squall Lines. J.Atmos.Sci, 45, 463-485.

FIG. 2: pressure, wind and precipitation as observed at Paloma Buoy meteorologial station and as forecast by WRF model hours before, during and immediately after the “olympic storm”.

III. RESULTS The difficulty in classifying this severe weather event is due to enhanced intensities in the frame of a generally not unusual meteorological pattern that characterized the “olympic storm”. We have collected all the measures available whose analysis seem to push ahead the idea of an early stage “bow echo” in the time window charactertized by the most severe and extended damages on the ground. Models cannot help in forecasting occurrences like that, but future research could underline correlations between meteorological measures able to improve the nowcasting reliability. In particular, the role of the Low Level Jet entering from the Pala d'Altei could be a good point for potentially strong storms trigger.

IV. AKNOWLEDGMENTS The authors would like to thank: Andrea Buzzi, Silvio Davolio and Andrea Malguzzi (ISAC – CNR, Bologna, Italy) for the preciuos suggestions and for having made available the entire MOLOCH simulation suite; Neva Pristov (ARSO – Lubiana, Rep. of Slovenia) for the ALADIN simulation suite; Irene Gallai of CRMA ARPA FVG (Palmanova, Italy) for the WRF - ARW version 3 simulations initialized on GFS and ECMWF; the CREST s.r.l. staff (Trieste, Italy) for the WRF – ARW version 2 simulation initialized on GFS; Richard Rotunno (NCAR, USA) for the relevant help in classification problems.

V. REFERENCES Wakimoto R.M., Murphey H. V., Davis C. A., Atkins N. T., 2006: High Winds Generated by Bow Echoes. Part I: Overview of the Omaha Bow Echo 5 July 2003 Storm during BAMEX. Mon.Wea.Rev., 134, 2793-2812. Wakimoto R.M., Murphey H. V., Davis C. A., Atkins N. T., 2006: High Winds Generated by Bow Echoes. Part II: The Relationship between the Mesovortices and Damaging Straight-Line Winds. Mon.Wea.Rev., 134, 2813-2829. Atkins N. T., St.Laurent M., 2009: Bow Echo Mesovortices. Part I: Processes That Influence Their Damaging Potential. Mon.Wea.Rev., 137, 1497-1513.

274 5th European Conference on Severe Storms 12 - 16 October 2009 - Landshut - GERMANY

VORTEX2: The Second Veriﬁcation of the Origins of Rotation in Tornadoes Experiment

Howie Bluestein1, Don Burgess2, David Dowell3, Paul Markowski4, Erik Rasmussen5, Yvette Richardson6, Lou Wicker7, Josh Wurman8

1University of Oklahoma, Norman, Oklahoma, USA, [email protected] 2University of Oklahoma / Cooperative Institute for Mesoscale Meteorological Studies, Norman, Oklahoma, USA, [email protected] 3National Center for Atmospheric Research, Boulder, Colorado, USA, [email protected] 4Penn State University, University Park, Pennsylvania, USA, [email protected] 5Rasmussen Systems, Mesa, Colorado, USA, [email protected] 6Penn State University, University Park, Pennsylvania, USA, [email protected] 7National Severe Storms Laboratory, Norman, Oklahoma, USA, [email protected] and 8Center for Severe Weather Research, Boulder, Colorado, USA, [email protected]

I. INTRODUCTION VORTEX2 relies on what might be referred to as “distributed leadership,” that is, the coordination and operation philoso- The Verification of the Origins of Rotation in Tornadoes phy relies largely on field teams carrying out their missions Experiment (VORTEX) is a multi-agency field program to in- semi-autonomously based upon information assimilated by vestigate tornado genesis, maintenance, and demise; tornado a field coordination team and distributed to individual team structure and near-ground winds; relationships between tor- leaders. nadic storms and their environments; and numerical predic- II. THE ECSS PRESENTATION tion of supercells and tornadoes. The first field phase of VOR- TEX occurred in 1994 and 1995. The second field phase of The presentation to be delivered at the ECSS will dis- VORTEX—VORTEX2—is taking place in the United States cuss the science objectives, instrumentation, and highlights Great Plains region during the spring of 2009 and 2010. The from Year 1. Additional information on VORTEX2 is avail- field experiment is being conducted with mobile facilities, able at http://www.vortex2.org (maintained by the Center for without a “home base” per se (Fig. 1). This “fully mobile” Severe Weather Research), http://www.nssl.noaa.gov/vortex2 strategy is necessary to obtain the needed high-resolution ob- (maintained by the National Severe Storms Laboratory), and servations in the limited time available for the field phase. http://www.eol.ucar.edu/projects/vortex2 (maintained by the VORTEX2 will also benefit from data collection by the fixed National Center for Atmospheric Research). observing network in the Great Plains, particularly the rich observing network in Oklahoma. The Year 1 field phase of VORTEX2 took place from 10 May–13 June 2009. Year 2 activities are slated for 1 May– III. ACKNOWLEDGMENTS 15 June 2010. The selected time period for operations covers the part of the spring storm season that tends to have slower- VORTEX2 is sponsored by the National Science Founda- moving storms, thereby presenting a better opportunity to ob- tion (NSF) and the National Oceanic and Atmospheric Ad- tain the high-resolution observations needed in support of the ministration (NOAA) of the United States. Participating or- science objectives (the science objectives of VORTEX2 are ganizations include the Center for Severe Weather Research, discussed in detail in the Scientific Program Overview, avail- Center for Interdisciplinary Remotely-Piloted Aircraft Stud- able at http://www.eol.ucar.edu/projects/vortex2/documents). ies, Cooperative Institute for Mesoscale Meteorological Stud- The VORTEX2 fleet of mobile instruments comprises ap- ies, Environment Canada, Lyndon State College, National proximately 50 vehicles, including 10 radars (W-, Ka-, X, and Center for Atmospheric Research, National Severe Storms C-band radars; also two dual-polarization radars, a phased Laboratory, North Carolina State University, Penn State Uni- array radar, and a rapid-scanning radar), 4 mobile sounding versity, Purdue University, Rasmussen Systems, State Univer- units, 8–10 mobile mesonet units, a field coordination vehicle, sity of New York (SUNY) at Oswego, Texas Tech University, and teams that can deploy up to 24 StickNet probes, 12 tor- University of Colorado, University of Illinois, University of nado in situ probes, laser disdrometers, video particle probes, Massachusetts, University of Nebraska, and University of Ok- and, in some situations, unmanned aircraft systems (UAS). lahoma.

275 2

storm-scale radars (C-band)

-105 -100 -95 -90

0 10 20 km 45 45 SR1 SR2 storm motion mesocyclone-scale radars (X-band, two dual-pol)

40 UAS 40 CSWR, Hays DOW6 DOW7 NCAR garage

X UMASS XPOL NOXP 35 NWC W tornado-scale radars central OK 35 (W-, Ka-, X-band) P TTU resources X X

C C RapidScan UMASS W-band DOW 30 30 photogram- C X P W mobile rawinsonde mesonet metry site C-band X-band dual- W-band mobile polarization mobile mobile tornado Doppler Doppler mobile radar Doppler disdrometers CIRPAS TTU Ka-band -100 -95 StickNet pods and 2DP probes MWR-05XP in situ (phased array) tornado laser disdrometers and rawinsondes (4) StickNet (24) probes (12) mobile mesonet (8-10) video particle probes UAS coordination V2 Operations vehicle Center (VOC) in Norman, OK

FIG. 1: (Left) The VORTEX2 domain (orange) and other key locations: subdomain of central Oklahoma resources (including the NWRT Multifunction Phased Array Radar); National Weather Center (NWC, including National Severe Storms Laboratory and University of Okla- homa); Lubbock, Texas (Texas Tech University); repair bay in Hays, Kansas; UAS demonstration subdomain; and Boulder, Colorado (Center for Severe Weather Research, National Center for Atmospheric Research, and University of Colorado). (Middle) An idealized deployment of VORTEX2 facilities targeting a slow-moving supercell. (Bottom and right margins) VORTEX2 instrumentation.

276 5h European Conference on Severe Storms 12 - 16 October 2009 - Landshut - GERMANY

THE DEVELOPMENT OF TORNADIC STORMS NEAR A SURFACE WARM FRONT IN CENTRAL ENGLAND DURING THE CONVECTIVE STORM INITIATION PROJECT (CSIP) P. Groenemeijer*, U. Corsmeier, Ch. Kottmeier

Institut für Meteorologie und Klimaforschung, Karlsruhe Insititute of Technology, Karlsruhe, Germany, [email protected] * current affiliation: Institute of Meteorology, University of Munich, Germany

I. INTRODUCTION parameters were calculated. These include the CAPE below Strong tornadoes are a rare occurrence across the British 3 km AGL and the 0-1 km storm-relative helicity, displayed Isles. Despite the fact that convective instability as measured in Fig. 3. Note that the location of greatest overlap of these by CAPE (latent instability) is usually rather low, they two quantities was near the location “B”, which indicates the occasionally do occur. It is known that large CAPE is not location of the storm that later produced the tornado. required for the formation of strong tornadoes, proven by a large number of counter-examples, including the recent violent tornado in Hautmont, France (Mahieu and Wesolek, 2009). In such cases, other factors must play an especially important role. As will be shown, a frontal boundary proved to be very important in this specific case. The relevance of boundaries to the development of low-level rotation and tornadoes has been identified in the past by Markowski et al. (1998) and Rasmussen et al. (2000). Here, we present an investigation of the mesoscale environment of severe convective storms that developed on July 28th 2005 during the CSIP field campaign (Browning et al., 2007). One of the storms produced an F2 tornado in downtown Birmingham at 1330 UTC (Marshall and Robinson, 2006), and two other tornadoes occurred later on the day near Peterborough and the village of Moulton (Fig. 1).

FIG. 2: Interpolated 2 m temperature in °C and 10 m wind fields at 1200 UTC. “B” represents the location of the storm that later produced the tornado in Birmingham.

FIG. 1: Map of England and Wales showing the locations of the tornadoes, the available radiosondes and the CSIP field campaign area. 2 -2 FIG. 3: Interpolated 0-1 km storm-relative helicity(m s ) and CAPE II. PRESENTATION OF RESEARCH below 3 km (J/kg). The presented analysis is based both on observational data and a numerical simulation. The observational data, that A numerical simulation was carried out using the included both surface data and radiosonde data were COSMO model (Schättler et al., 2007). The grid spacing of interpolated on a Cartesian grid using a Barnes algorithm the model was reduced to 1.1 km, compared with the (details available upon request). Two near-surface fields are operationally used 2.8 km. shown in Fig. 2: the 2 m temperature and 10 m wind at 1200 The resulting simulation develops storms containing UTC, approximately 1:30 hours before the F2 tornado rotating convective updrafts that exhibit low-level rotation. occurred. The location of a warm frontal boundary is Low-level moisture, wind and precipitation rates are displayed. From the three-dimensional fields, several displayed in Fig. 4. The low-level vertical vorticity (not

277 5h European Conference on Severe Storms 12 - 16 October 2009 - Landshut - GERMANY shown) of the simulated storm “S” is maximized shortly III. CONCLUSIONS after crossing the frontal boundary from the south. The We have studied the development of a storm that developed Combination of relatively high values of storm-relative with relatively low CAPE but within an otherwise helicity and slightly higher CAPE in a narrow zone on the favourable environment for updraught rotation. Using a cold side of the boundary are thought to be the primary combination of actual observations and numerical causes for this. The reason for the relatively high CAPE can modelling. It was found that... be traced back to an accumulation of low level moisture i) a narrow zone of increased low-level moisture north of the boundary. This accumulation likely occurs formed north of the surface front, which created a narrow because of a relative lack of turbulent entrainment of drier zone of enhanced, but still modest, CAPE values and very air into a very shallow boundary layer, combined with low cloud base heights. relatively strong evapotranspiration. ii) within the same zone, backed surface winds created ample storm-relative helicity, that probably played an important role in the development of rotation iii) the COSMO model, being run at 1.1 km resolution, was able to reproduce weak storm rotation (vorticity on the order of 1·10-2 s-1), which was highest int he lowest kilometre of the atmosphere. iv) weak mixing within the boundary layer north of the front was both responsible for the strongly veering wind profile with height that lead to the high storm-relative helicity, and for the accumulation of low-level moisture that created relatively strong low-level boundary for parcels lifted from the surface. The combination of those factors proved sufficient for the development of a strong tornado.

IV. ACKNOWLEDGMENTS We thank Christian Barthlott for his assistance with the COSMO simulations. We acknowledge the U.K. Met Office for providing surface data and radiosonde data used for the analysis. This work was partly funded by the HGF Virtual Institute VH-VI-133 “COSITRACKS” of the Helmholtz FIG.4: Mixing ratio at 1000 hPa, wind at 10m AGL, and Gemeinschaft. precipitation rates, simulated with the COSMO model at 1.1. km grid-spacing, starting at 0600 UTC, and initialized with data from a coarser COSMO run at 7 km grid-spacing, which was nested into V. References ECMWF IFS analyses. Browning, K., et al., 2007: The Convective Storm Initiation Project. Bull. Amer. Meteor. Soc., 88, 1939-1955. Hanstrum, B.N., G.A. Mills, A. Watson, J.P. Monteverdi, and C.A. Doswell, 2002: The Cool-Season Tornadoes of California and Southern Australia. Wea. Forecasting, 17, 705–722. Mahieu, P, Wesolek, E., 2009: The deadly EF-4 tornado of August 3, 2008, in northern France. Preprints, 5th European Severe Storms Conference, Landshut, Germany 12-16 October 2009. Markowski, P.M., E.N. Rasmussen, and J.M. Straka, 1998: The Occurrence of Tornadoes in Supercells Interacting with Boundaries during VORTEX-95. Wea. Forecasting, 13, 852–859. Marshall, T. and S. Robinson, 2006: The Birmingham, UK Tornado: 28 July 2005. In Preprints, 23rd Conference on FIG.5: North-south profiles (from bottom to the top of Fig. 4, but at Severe Local Storms, 6-10 November 2006, St. Louis, 1300 UTC) of temperature and dew point at 1000 hPa, the 10 m MO, USA. wind, and CAPE for a parcel lifted from the 1000 hPa-level. Rasmussen, E.N., S. Richardson, J.M. Straka, P.M. Markowski, and D.O. Blanchard, 2000: The Association A cross-section of various parameters can be seen in of Significant Tornadoes with a Baroclinic Boundary on 2 Fig. 5. It can be seen that CAPE is maximized in a 30 km- June 1995. Mon. Wea. Rev., 128, 174–191. wide zone north of the wind-shift line. This is perhaps Schättler, U., G. Doms, and C. Schraff, 2007: A description counter-intuitive because, on a larger scale, the of the nonhydrostatic regional COSMO-model, Part VII: thermodynamic properties of the air-mass south of the front User's Guide. Available at: http://www.cosmo-model.org. appear to be more prone to convective development, as it is Seifert, A., M. Baldauf, J. Förstner, T. Hanisch, C. Schraff, moister and warmer. and K. Stephan, 2007: Forecasting of severe weather with the convection-resolving model COSMO-LMK. Preprints, 4th European Conference on Severe Storms, 10-14 September 2007, Trieste, Italy.

278 5th European Conference on Severe Storms 12 - 16 October 2009 - Landshut - GERMANY

Impact of dryline misocyclones on convection initiation on 19 June 2002 during IHOP

Yvette P. Richardson1, Conrad L. Ziegler2, Michael Buban3, James N. Marquis1, and Joshua M. Wurman4 1The Pennsylvania State University, University Park, PA, USA, [email protected] 2National Severe Storms Laboratory, Norman, OK, USA, [email protected] 3University of Oklahoma, Norman, OK, USA, [email protected] and 4Center for Severe Weather Research, Boulder, CO, USA, [email protected] (Dated: September 15, 2009)

I. INTRODUCTION

The International H2O Project (IHOP 2002) was held from 13 May to 25 June of 2002 in the Southern Great Plains region of the United States, with a goal of improving our understanding of the 4-D water vapor field and its interaction with the wind field. In particular, it was hoped that analyses of the high-resolution wind and thermodynamic data collected would better our understanding of water vapor heterogeneity as well as the processes involved in convection initiation. A vast array of instrumentation was deployed, including mobile Doppler radars, mobile mesonet vehicles (i.e., cars with roof- mounted instrumentation), mobile sounding units, aircraft in- situ probes, airborne Doppler radars, airborne lidar, and numerous fixed instruments in the Oklahoma panhandle. In this study, we focus on the convection initiation thrust of FIG. 1: Conceptual model of convergence along an atmospheric the IHOP 2002 campaign. In particular, we examine the role boundary containing misocyclones. The influence of the misocy- of small-scale vortices (misocyclones) in the initiation of con- clones on the vertical velocity depends on their size compared to the vection on 19 June 2002 along a dryline in northern Kansas. width of the boundary, and the merger of neighboring misocyclones often is found to significantly distort the boundary. (adapted from Marquis et al. 2007) II. BACKGROUND dynamic data coverage from the thin strips generally collected Knowing when and where convection will initiate remains along roads or airplane transects, we use a Lagrangian tech- one of the more difficult problems facing forecasters. It has nique (Ziegler et al. 2007) in which the multi-Doppler derived long been recognized that atmospheric boundaries (e.g., cold wind field is used to advect thermodynamic information from fronts, drylines, etc.), with their associated upwelling of wa- its original observation location along backward and forward ter vapor, often are preferred initiation locations, but it is trajectories. less clear why certain portions of a boundary develop convection before others, although many studies (e.g., Wilson et al. 1992) suggested that small-scale circulations associated with the wind-shift along a boundary may organize the vertical ve- III. 19 JUNE 2002 ANALYSES locity field in such a way that certain areas become preferred locations for sustained parcel lifting. A detailed analysis of The IHOP mobile armada intercepted a dryline near Colby, high-resolution multi-Doppler radar data obtained in several Kansas on 19 June 2002. This particular dryline was a prolific boundaries containing misocyclones during IHOP 2002 re- producer of misocyclones and dust devils, and storms initiated vealed such an organizing effect (Marquis et al. 2007, Fig. 1), along portions of it. Mobile mesonet water vapor mixing ra- and the merger of neighboring misocyclones as their popu- tio data obtained as probe 1 traversed a misocyclone just prior lation evolves was found to severely distort the boundary in to vortex merger (Fig. 2) indicate a transition of about 3 g some cases, with trajectory analyses suggesting the merger kg−1 over less than 5 km with a strong wind shift. A verti- process may act as an effective mechanism for mixing air cal cross-section (Fig. 3) captures the interaction between the mass properties across the boundary. misocyclone and the dryline circulation. A Lagrangian analy- In this study, we combine multi-Doppler wind analyses sis at this time (Figs. 4 and 5), illustrates the distortion of the with mobile mesonet, mobile sounding, airborne lidar, and water vapor field in the vicinity of misocyclones that are in photogrammetric cloud observations to examine in greater de- the process of rotating about one another and merging. Sim- tail the link between misocyclones and cloud formation, as ilar analyses will be carried out for other time periods and well as the influence of misocyclones in organizing the water combined with cloud analyses derived from photogrammetry vapor field along the boundary. In order to expand the thermo- as well as water vapor fields from airborne lidar to produce a

279 2

−1 FIG. 2: Ground-relative horizontal wind, vertical vorticity (con- FIG. 4: As in Fig. 2 but shading is water vapor mixing ratio in g kg toured every 5x10−3 s−1 with zero excluded), and reﬂectivity from a Lagrangian analysis of in-situ observations. (shaded) at the surface at 2215 UTC on 19 June 2002. The station models show mobile mesonet probe 1 data collected from four minutes before until ﬁve minutes after the analysis time. In the station model, the upper number is the virtual potential temperature in ◦C, the lower number is mixing ratio in g kg−1, and a full wind barb is 10 m s−1.

FIG. 5: As in Fig. 4 but for a vertical (E-W) cross-section through (14, 17.2) in Fig. 4.

National Science Foundation grants ATM-0638572 and ATM- 0638512.

FIG. 3: As in Fig. 2, but for a vertical (SW-NE) cross-section through (14, 14.5) in Fig. 2 intersecting the southernmost vortex in the pair V. REFERENCES of vortices. Winds are relative to the moving misovortex.

Wilson, J.W., G.B. Foote, N. A. Crook. J. C. Fankhauser, complete picture of convection initiation on this day and the C. G. Wade, J. D. Tuttle, C. K. Mueller, and S. K. Krueger, role of misocyclones in that process. 1992: The role of boundary-layer convergence zones and horizontal convective rolls in the initiation of thunderstorms: A case study. Mon. Wea. Rev., 120, 1785 - 1815. IV. ACKNOWLEDGMENTS Marquis, J. N., Y. P. Richardson, and J. M. Wurman, 2007: We are grateful to all of the scientists who participated in Kinematic observations of misocyclones along boundaries the IHOP 2002 ﬁeld campaign. This work was supported by during IHOP. Mon. Wea. Rev., 135, 1749-1768.

280 The Balkan cyclone Miodrag Stojanovic

Republic Hydrometeorological Service of Serbia, Kneza Viseslava 66, Belgrade, Serbia, [email protected]

I. INTRODUCTION

On the Balkan Peninsula and in its neighborhood there are five known cyclogenetic regions: Ligurian see, north Adriatic see, Pannonian plains, Romanian Wallachia and Aegean see.

II. PRESENTATION OF RESEARCH

Trough the few past years there are cases of diferent origination place. On june, 27th 2008. such a case happened. The cyclon developed in Hercegovina (6) (west part od the Balcans) and very slowly crossed the Balcan panninsula in west-southwest stream. It looked like few mesocyclones developed when the cold front passed the peninnsula. In this study it will be shown everything that happened in Serbia on this day, including surface maps, satellite and radar pictures, soundings and forecast charts.

281

III. RESULTS AND CONCLUSIONS

This case, and the other that are not presented in this work, shows that there is one additional origination place on the Balcans.

IV. AKNOWLEDGMENTS

In this work I used variety of surface maps from DWD, satellite pictures from EUMETSAT, radar pictures from croatian radar Bilogora and serbian radar network, soundings from University of Wyoming and forecast charts from WeatherOnline, Ogimet and Wetterzentralle.

V. REFERENCES

Dj. Radinovic, 1968: Weather analysis, 5 124-136

282 5h European Conference on Severe Storms 12 - 16 October 2009 - Landshut - GERMANY

SEVERE WINTER STORMS OVER THE WESTERN AND CENTRAL STATE OF SÃO PAULO, BRAZIL Ana Maria Gomes and Gerhard Held

Instituto de Pesquisas Meteorológicas-IPMet, São Paulo State University-UNESP, Bauru-Brazil, [email protected] (Dated: 15 September 2009)

I. INTRODUCTION storm and track files. The TrackGridStats application has The State of São Paulo is situated in the south-eastern produced analyses of storm tracks for all periods with storm region of Brazil and is, in general, characterized by summer activity during July 2007. To derive the spatial distribution rain and relatively dry winter months. The region is under of storm precipitation and storm duration during July 2007, the influence of both tropical and mid-latitude, large-scale the storm areas were defined by the 25 dBZ reflectivity synoptic systems. Severe thunderstorms can occur at any threshold, and all identified areas that exceeded the adopted time of the year, although they are less frequent during the threshold within the quantitative range of both radars, were dry winter months. Most of the significant weather occurs considered. between October and March, when the supply of solar energy and humidity is greatest, but severe winter storms, III. RESULTS AND CONCLUSIONS usually associated with baroclinic systems, do occur within Synoptic Overview for July 2007 the range of IPMet´s two S-band Doppler radars, which During July 2007, at least seven transient systems covers most of the State of São Paulo. This study presents an were observed over Brazil and five of these systems were analysis of the anomalous winter storms during July 2007, frontal waves that had originated in the south and southeast which have produced considerable damage over parts of the regions (CPTEC, 2009), producing some of the very State, as well as a precipitation field in excess of 300 mm favorable large-scale environments, such as frontal systems over its central and western regions. A case study for 24 July and high-level cyclonic vortices that were all enhanced and 2007 is presented, focusing on the storm properties related to have generated the extreme events observed in the State of the hail-producing cells and the hail metrics parameters of São Paulo. An anomalous precipitation field between 200 the NCAR software TITAN (Thunderstorm Identification, and 300 mm above the expected mean over the central and Tracking, Analysis and Nowcasting; Dixon and Wiener, western regions of the State was observed (Figure 2), 1993). The data used for the analysis were from IPMet´s two changing completely the spatial distribution of rainfall for Doppler radars located at Bauru (Lat: 22°21.5’ S, Lon: this relatively dry month, which is characterized by average 49°1.7’ W, 624 m amsl) and Presidente Prudente (Lat: rainfall within a range of 20 to 30mm for most of the State 22°10.5’ S, Lon: 51°22.5’W, 420 m amsl), respectively of São Paulo, except in the south and costal areas. (Figure 1). The main characteristics of both radars are: 2° beam width, 450 km range for surveillance mode and 240 km in volume scan mode, with 16 elevations (0.3° to 45°), 250 m radial and 1° azimuthal resolution, and a temporal resolution of 15 minutes or less, recording and archiving reflectivity, radial velocity and spectral width.

FIG 2: Precipitation anomaly for July 2007. Modified from CPTEC (2009), available at www.cptec.inpe.br.

FIG. 1: Doppler radar network of IPMet (BRU = Bauru; PPR = Radar Rainfall for July 2007 Presidente Prudente), showing the 240 and 450 km range rings. The rainfall distribution for July 2007, obtained from radar data deploying the well known Marshall-Palmer (MP) II. PRESENTATION OF RESEARCH equation for the Z-R relationship, is shown in Figure 3, The TITAN system in ARCHIVE mode was deployed where the major accumulation, in excess of 200 mm, located and tracking properties form the base for the analysis in the central and western parts of the State of São Paulo, is presented here. A TITAN cell was defined by the 40 dBZ in good agreement with the results given by the observed threshold for the reflectivity and 50 km3 for the volume, surface rainfall, shown in Figure 2. Similar results were observed at least in two volume scans (15 minutes). The obtained from the analysis of the spatial distribution of total rain field observed by IPMet´s radars for July 2007 was storm duration for July 2007, highlighting areas where obtained using the climatological module of TITAN that storms occurred for up to >15 hours during this period, as computes geographically-distributed statistics from TITAN shown in Figure 4.

283 5h European Conference on Severe Storms 12 - 16 October 2009 - Landshut - GERMANY

FIG 5: Storm track (light-green) showing cells that have produced

severe hail during the 24 July 2007 event. FIG 3: Storm precipitation distribution using composite reflectivity from both IPMet radars during July 2007. Many other places located within the path of this forecast track area have also reported hail on this day. TITAN with its built in algorithms that allow identification of potential severe storm “signatures” is certainly an important tool to be deployed in operational warning centers.

FIG 4: Storm duration distribution using composite reflectivity from both IPMet radars during July 2007.

The spatial distribution of storm duration shows that in the central and western parts of the State, storms with durations of 12 to 15 hours were traversing the region, contributing to the observed anomalous rainfall during July 2007. Such information, making use of the meteorological radars in the State of São Paulo and now available from TITAN, is very useful for agriculture and water planning purposes. Severe thunderstorms are a significant threat throughout the State of São Paulo, frequently causing extreme damage to agriculture, industry and property, including the occasional loss of lives. During the 2007 winter season, extensive damages to agriculture and property, caused by hailstorms observed mainly in the FIG 6: SSS index distribution for 15:05 LT (a) and the forecast for 15:35 LT (b) when hail was confirmed in the Taiuva rural area central areas of the State, were reported by newspapers, TV, during the 24 July 2007 event. etc. IV. ACKNOWLEDGMENTS Hail Event of 24 July 2007 The authors would like to thank J. M. Kokitsu for the Figure 5 shows the full tracks defined by the 40 dBZ implementation of TITAN routines used in the analysis and reflectivity threshold on 24 July made by hailstorms that Drs J. Wilson and M. Dixon of NCAR for facilitating the swept the northern areas of the State, causing extensive implementation of TITAN at IPMet/UNESP. damage to orange plantations and resulting in a loss of 30% of the production, with direct implications for the coming V. REFERENCES year´s harvest according to farmers of these particular Dixon M. and Wiener G., 1993: TITAN: Thunderstorm regions. Figures 6a and 6b show a severe cell structure, Identification, Tracking, Analysis and Nowcasting - A radar- represented by the SSS index (Visser, 2001) and its forecast based methodology. J. Atmos. Ocean. Technol., 10, 785-797. for the next 30 minutes, when the storm was to reach the Visser, P.J.M., 2001: The Storm-Structure-Severity method for the rural area of Taiuva town. The hailstorm had resulted in identification of convective storm characteristics with conven- severe damage to the local agricultural community. tional weather radar. Meteorological Applications, 8,1-10.

284 5h European Conference on Severe Storms 12 - 16 October 2009 - Landshut - GERMANY

HARE – A NEW INTELLIGENT HAIL RECORDER FOR NETWORKS AND FIELD CAMPAIGNS

Martin Löffler-Mang

University of Applied Sciences, Goebenstr. 40, D-66117 Saarbrücken, Germany, [email protected]

(Dated: 15 September 2009)

I. INTRODUCTION tom). Each hail event is stored in the internal memory to- In this abstract the prototype of a new intelligent hail re- gether with date and time. The memory can be read out via corder (HARE) is described. An online device as well as an serial port at any time after one ore more hail events. autonomous one are available for a large number of possible applications. Nowadays hail typically is still measured with so-called hailpads. These are normally pieces of Styrofoam covered with a thin aluminum foil. After a hail event the hailpad has dints which can be evaluated. After evaluation the hailpad has to be replaced. There is no online information during hail storm, not even information on date and time of hail fall.

II. SENSOR DEVELOPMENT An intelligent and simple hail sensor was developed, based on signal production with microphones, a quick signal analysis and recording possibility. For HARE small piezo- FIG 2: Sensor signals from top and bottom plate. electric microphones inside a Macrolon body are used to detect hailstones. The prototype shown in fig. 1 has an III. MEASUREMENTS AND CALIBRATION octagonal shape, two microphones on top and bottom plate From the signals shown in fig. 2 it was a large step to the in the middle of the device, and a small electronic board. final signal analysis. Main idea was to calculate mean signal The reason for the octagonal shape was to avoid poor signals values for defined time intervals. One example of those from hits just in the corners of a square. mean values is given in fig. 3. For a wood sphere of 15mm in diameter the decreasing amplitude is plotted as a function of time. The good damping of the housing material can be seen and after approx. 7ms the device would be ready for the next impact.

FIG. 3: Mean amplitude damping with time.

The hailstones are classified in four danger categories. FIG. 1: Hail recorder prototype with sensors and electronics. Mean theoretical values of diameter, velocity, mass, momentum, and energy of these classes are given in tab. 1. A hailstone hitting on the surface produces waves on the sensor body and a voltage in the piezo-electric microphones, Diameter Velocity Mass Momentum Energy see fig. 2. Obviously the top signal starts first and shows d [mm] v [m/s] m [g] p [kg·m/s] Ekin [J] some disturbances at the beginning. Using top and bottom 5 5 0,06 3,01E-04 7,53E-04 sensors makes the device more independent from the loca- 15 9 tion of the hailstone hits (similar results in the middle or at 1,63 1,46E-02 6,58E-02 the edge). The voltage depends on the strength of the hit. 25 12 7,53 9,03E-02 5,42E-01 After A/D-conversion a micro-controller estimates the hail- 35 14 20,65 2,89E-01 2,02E+00 stone size in combining both sensor signals (top and bot- TABLE 1: Hailstone parameters (mean values).

285 5h European Conference on Severe Storms 12 - 16 October 2009 - Landshut - GERMANY

To relate the measurements to the danger of damage it is necessary to calibrate the sensor. For this purpose a hail gun 1000 was built. There is a European testing standard for solar 900 panels the gives the rules. Ice spheres with a diameter of 800 25mm and a velocity of 22m/s have to be shot on the panels. 700

600 Water 500 Sprudel Orange 400 HARE signal [digits] juice Tomato juice Carott 300 juice Ma us b all 200 0 0,02 0,04 0,06 0,08 0,1 0,12 0,14 0,16 0,18 0,2

momentum [kg*m/s]

FIG. 6: Calibration results for different ice balls.

The experiments were controlled by a LabView software. With this software the user set the pressure of the hail gun, e.g. the velocity of the ice balls, started the light sheets, and finally, shot. As output the signal was shown on the screen, the velocity was evaluated and the data of each shot were stored in an excel file.

IV. APPLICATIONS First application idea was to use the online HARE at FIG. 4: Pneumatic hail gun with HARE below. Spanish solar power plants to prevent the expensive modules from damage, see fig. 7. The serial port will be replaced by In the top of fig. 4 the gun can be seen and there is a hail some bus communication, e.g. SDI-12 bus. The hail sensors recorder below the frame constructed with Bosch profiles. around the solar plant are directly connected to the control Just above the HARE two laser light sheets are mounted for room and deliver a warning when a hailstorm is coming. velocity detection of ice balls. They were specially produced Then the drives of the solar modules bring them into the according to the above mentioned standard. Some examples most save position. First tests of this application will be of water and orange juice ice balls are shown in fig. 5. Dif- conducted during spring and summer 2010. ferent materials were used to simulate hail with various den- sities and textures.

FIG. 7: HARE, solar power plant, and author. FIG. 5: Example of ice balls from water and orange juice. Latest application for the autonomous HARE will be a More than 100 shots with velocities from 10m/s up to small network of at least ten stand-alone devices within a 30m/s were conducted with different ice balls. The overall hailstorm project in the Black Forest around Villingen- calibration data are shown in fig. 6. The HARE signal given Schwenningen. Hopefully, in 2010 the first real hail data in internal digits is presented as a function of ice ball mo- will be produced from this campaign. mentum. The momentum was calculated by the measured velocity and the weight of each single ice ball taken before V. REFERENCES the shot. The results of different materials are sorted by [1] Löffler-Mang M., Joss J.: An Optical Disdrometer for symbols and colors. In addition, six measurements of a free Measuring Size and Velocity of Hydrometeors. J. At- falling mouse ball are included. They are connected by a line mos. Oceanic Techn. 17 (2000), 130-139. and show the elastic border. Nearly all ice balls smash on the HARE surface, their signals are smaller than the mouse ball [2] Löffler-Mang M., Blahak U.: Estimation of Radar signals. Also obvious are the smaller signals of orange juice Reflectivity from Measured Snow Spectra. J. Appl. balls, resulting from a lower density and a softer texture. Meteorol. 40 (2001), 843-849.

286 5th European Conference on Severe Storms 12 - 16 October 2009 - Landshut - GERMANY

MOBILE SOUNDING MEASUREMENTS OF THE NEAR-STORM ENVIRONMENT DURING VORTEX2 Matthew D. Parker1, Adam J. French1, Casey E. Letkewicz1, Matthew J. Morin1, Katherine Rojowsky1, David Stark1, and George H. Bryan2

1Department of Marine, Earth, & Atmospheric Sciences, North Carolina State University, Raleigh, NC, USA 2 Mesoscale and Microscale Meteorology Division, National Center for Atmospheric Research, Boulder, CO, USA (Dated: 14 September 2009)

I. INTRODUCTION sampled by the VORTEX2 armada. The inflow sounding (Fig. 4) reveals very large vertical wind shear and CAPE, The first field campaign of the Verification of the Origins of with a nearly adiabatic lapse rate extending up through 500 Rotation in Tornadoes Experiment 2 (VORTEX2) was held hPa (for more, see Parker 2009, elsewhere in this volume). from 10 May - 13 June 2009 in the central U.S. VORTEX2 is a fully nomadic project targeting in-storm and near-storm Secondary and ad hoc deployment plans measurements of tornadoes and supercellular thunderstorms. Among approximately 50 instrumented vehicles fielded for If storms are fast-moving, in a sparse road network, or VORTEX2 are four mobile GPS advanced upper air clearly non-supercellular, other near-storm deployments are sounding (MGAUS) systems. During the 2009 field phase, used, such as a mesoscale box (Fig. 5) or picket fence (Fig. we made 217 successful launches on 21 different operations 6). Although such strategies do not sample the storm-scale days, including 69 pre-convective soundings and 148 variability as well, they are safer and also often provide a soundings in the vicinity of mature storms. Quality control depiction of mesoscale heterogeneity that is startling. For and initial processing of the data are currently underway; the example, the black and green soundings in Fig. 6 were conference poster provides a first look at several launched within 5 minutes and roughly 20 km of one deployments from the 2009 campaign. another. Even so, they reveal very different inflow environments, with the temperature inversion and associated convective inhibition (CIN) being completely absent from II. DEPLOYMENT STRATEGIES the eastward member of the pair (Fig. 7).

A. Pre-storm Environment III. LESSONS LEARNED AND FUTURE PLANS

A primary MGAUS aim is to characterize the pre-convective MGAUS teams became quite adept at near-storm sampling environment within which storms develop. These data are during the 2009 campaign; MGAUS systems are well-suited used in real time for forecast refinement, and will be used in to depicting variability of the storm-scale environment. retrospective analysis of the VORTEX2 cases. The higher However, preliminary analyses suggest that soundings are temporal and spatial resolution of the MGAUS observations often lost or compromised in the forward flank of supercells, (when compared to the routine operational soundings) possibly because of icing and/or lightning. provides an excellent depiction of environmental variability In the coming months, we will complete quality and evolution. For example, on 13 June 2009, an impressive control procedures for the 2009 MGAUS data. The next capping inversion was present during much of the day (Fig. step will then be integration of the sounding data with the 1, left), but had been removed by the time of convective other VORTEX2 datasets collected in 2009. We will initiation in the region (Fig. 1, right). undertake the second observing phase during the window of 1 May - 15 June 2010. Going forward, we plan to amend B. Near-storm environment the MGAUS operations plan for the forward flank of supercells, wherein we often lose soundings pre-maturely Another primary MGAUS aim is to characterize the near- and data quality appears to be compromised. One possibility storm environment for target storms that are sampled by the is to sample the inflow environment more heavily, since VORTEX2 armada. there appears to be significant mesoscale variability in storms’ inflow sectors. Primary deployment plan

Many missions focused on documenting environmental IV. ACKNOWLEDGMENTS variability and baroclinity in the storm’s inflow, forward flank, rear flank, and anvil shading zones. Fig. 2 The measurements were funded by NSF Grant ATM- summarizes the frequency with which various parts of target 0758509, with equipment and support from NSSL and supercells were sampled by the MGAUS teams. An NCAR-EOL. EOL provided excellent technical expertise in example of an optimal MGAUS deployment is shown in Fig. the form of MGAUS operators and technicians, especially 3, wherein the inflow zone, upshear/rear flank zone, and the Tim Lim (EOL) who kept many, many things up and forward flank baroclinic zone were all sampled with running smoothly. simultaneous launches from our four vehicles. This launch occurred shortly after the dissipation of a tornado that was

287 5th European Conference on Severe Storms 12 - 16 October 2009 - Landshut - GERMANY

FIG. 1: MGAUS soundings from Dumas, Texas on 13 June 2009 from 1959 UTC (left) and 2303 UTC (right).

FIG. 5: Same as Fig. 3, except for 7 June 2009, with radar image from Kansas City, Missouri.

FIG. 2: Storm-relative MGAUS launch positions for 82 near- supercell soundings from VORTEX2 in 2009.

FIG. 6: Same as Fig. 3, except for 4 June 2009.

FIG. 7: MGAUS soundings on 4 June 2009 from 2303 UTC (black) and 2308 UTC (green). Launch locations and trajectories are color- coded with Fig. 6.

FIG. 3: Launch locations and trajectories for MGAUS deployment on 5 June 2009. Sounding positions are converted to be storm- relative with respect to radar image from Cheyenne, Wyoming.

FIG. 4: MGAUS sounding from 2240 UTC on 5 June 2009. Launch location and trajectory are in blue in Fig. 3.

288 5th European Conference on Severe Storms 12 - 16 October 2009 - Landshut - GERMANY

Mobile mesonet observations in VORTEX2

Yvette P. Richardson1, Paul M. Markowski2, Joshua M. Wurman3, Karen Kosiba4 1The Pennsylvania State University, University Park, PA, USA, [email protected] 2The Pennsylvania State University, University Park, PA, USA, [email protected] 3Center for Severe Weather Research, Boulder, CO, USA, [email protected] and 4Center for Severe Weather Research, Boulder, CO, USA, [email protected] (Dated: September 15, 2009)

I. INTRODUCTION

The first field year of the second phase of the Verification of the Origins of Rotation in Tornadoes Experiment (VOR- TEX2) was carried out 10 May - 13 June 2009 with the goal of collecting data in severe storms to address four main foci: tornadogenesis, maintenance, and demise; tornado near-ground wind fields; relationships among tornadoes, their parent thunderstorms, and the larger-scale environment; and numerical weather prediction of supercells and tornadoes. In order to answer the outstanding questions in each of these areas, simultaneous measurements of the wind and thermodynamic fields are necessary. A large array of mobile instrumentation, including Doppler radars, sounding units, disdrometers, StickNet probes, tornado in-situ probes, and mobile mesonet vehicles, collected complete 4-D wind and thermodynamic fields within several storms of varying morphology (e.g., multicell, supercell, and squall line), including one tornadic storm. In this paper, we highlight the data collection efforts of the mobile mesonet teams. FIG. 1: Idealized deployment of the mobile mesonet for a slow- moving storm.

II. MISSION OF THE MOBILE MESONET vancement of our knowledge about the important dynamical The official VORTEX2 mobile mesonet comprised six ve- processes during tornado formation depends critically on sam- hicles with rooftop meteorological instrumentation designed pling the wind field and the temperature field at the same time. to measure wind, temperature, relative humidity, and pres- Past studies using only one type of data or the other led to im- sure (Straka et al. 1996). These probes were developed portant theories that could be only partially confirmed with at the National Oceanic and Atmospheric Administration those datasets. In reality, fully coordinated data collection is (NOAA) National Severe Storms Laboratory (NSSL). One of often difficult to achieve owing to sparse road networks, poor the probes also served as the mobile mesonet coordination ve- communication networks, and storm hazards. hicle. At times, other vehicles within the VORTEX2 armada also served as part of the mobile mesonet upon completion of their primary mission (e.g., the tornado in-situ probe vehicles III. DATA COLLECTION ACHIEVED IN YEAR 1 operated by the Center for Severe Weather Research). The mobile mesonet contributes to all four foci of the VORTEX2 In VORTEX2, the ability to display radar reflectivity with project. all vehicle positions overlaid via the Situational Awareness In the idealized mobile mesonet deployment strategy for for Severe Storm Intercepts (SASSI) display greatly aided our a slow-moving storm (Fig. 1), each vehicle has a particu- ability to successfully accomplish our mission. As an exam- lar storm-relative mission such that all significant tempera- ple, data coverage during a time of strong low-level rotation is ture gradients are sampled. As tornadogenesis is one of the shown for the 11 June 2009 supercell in eastern Colorado in main foci of VORTEX2, greater concentration is placed on Fig. 2. For this case at this time, the most important regions the rear-flank region of the storm, within which the character- of the targeted cell are sampled well by the mesonet vehicles. istics of the cold pool are thought to play an important role in Although this cell was not tornadic, it provides an important the baroclinic generation of vorticity as well as its subsequent comparison case for the tornadic storm as it did have strong tilting and stretching. Indeed, one of the driving forces behind low-level rotation. Understanding why two storms that look the VORTEX2 field campaign was the realization that the ad- very similar are so different in their tornado production is one

289 2

similation of single-Doppler and thermodynamic data. The integration of multiple disparate datasets will be a signiﬁcant challenge but one that is necessary to move our knowledge 0005:05 UTC 12 June 2009 forward. Similar data collection efforts will be undertaken in the second year of VORTEX2 to be held 1 May to 15 June 2010.

2205:05 UTC 2 June 2009

305.0 305.5

306.0

r a d a r X U P K f o h t r o n m k

305.0 306.5 km north of KCYS radar km east of KPUX radar 305.5 307.0 306.0 FIG. 2: Mobile mesonet sampling for the 11 June 2009 supercell in 306.5 eastern Colorado near Las Animas. Each track corresponds to the 307.0 traverse of a mobile mesonet vehicle during the time of the radar volume. Radar data are from the KPUX 88D. km east of KCYS radar

FIG. 3: Preliminary analysis of mobile mesonet potential tempera- key to unraveling tornadogenesis. ture data for the 5 June 2009 tornadic supercell in eastern Wyoming. The first year of VORTEX2 occurred during a record low A steady-state assumption is made over a 10-min period centered on in the number of tornadic storms; thus, the potential for inter- each analysis time, which corresponds to the time of the low-level cepting tornadoes was severely limited within the VORTEX2 88D sweep. Data collected more than 2.5 minutes on either side of the analysis time are in gray. All winds are storm-relative and in domain. However, one tornadic storm in eastern Wyoming on knots. Radar data are from the KCYS 88D. 5 June 2009 provided an unprecedented coordinated dataset beginning approximately twenty minutes before tornado formation and continuing past tornado demise. A preliminary V. ACKNOWLEDGMENTS analysis of mobile mesonet potential temperatures for this case (Fig. 3) reveals a relatively small (∼ −1.5 K) potential temperature deficit in the rear-flank area compared to the am- The authors would like to thank all of the scientists who bient environment, in line with previous measurements made contributed to the collection of VORTEX2 data. This work within tornadic storms (Markowski et al. 2002). was supported by National Science Foundation grants ATM- 0801035 and ATM-0801041.

IV. FUTURE WORK VI. REFERENCES VORTEX2 is a highly collaborative project, and analysis of data from the first year of VORTEX2 is just beginning. The Straka, J. M., E. N. Rasmussen, and S. E. Fredrickson, data shown here will be combined with those from other plat- 1996: A mobile mesonet for finescale meteorological obser- forms to create a comprehensive picture of tornado formation vations. Journal of Atmos. and Oceanic Tech., 13, 921 - 936. and demise on 5 June 2009. Similar data for non-tornadic Markowski P. M., J. M. Straka, and E. N. Rasmussen, cases will be used for comparison to address the outstand- 2002: Direct surface thermodynamic observations within the ing questions that inspired VORTEX2. Analysis techniques rear-flank downdrafts of non-tornadic and tornadic supercells. will include dual-Doppler syntheses at multiple scales and as- Mon. Wea. Rev., 130, 1692-1721.

290 5th European Conference on Severe Storms 12 - 16 October 2009 - Landshut - GERMANY

CONVECTIVE STORMS OVER BASQUE COUNTRY: JUNE 2008 CASES STUDY

J. Egaña12, S. Gaztelumendi12, D. Pierna12, I. Gelpi12, K. Otxoa de Alda 12 1Basque Meteorology Agency (EUSKALMET), Miñano, Älava, (Spain). 2European Virtual Engineering Technological Centre (EUVE), Meteorology Division. Vitoria, Álava, (Spain).

I. INTRODUCTION During June 2008, different severe weather episodes related with convective storm events occur in the Basque Country area. In this paper, we present a selection of the most representative cases occurred during this month. The first case study is related with the intense rainfall in the northwest part of the Basque Country. June the 1st, Bilbao metropolitan area was affected by showers, collecting more than one hundred and twenty millimeters precipitation in twenty four hours. The second case study deals with moderate widespread storms, when precipitation over ten millimeters in ten minutes was collected in many points of the territory. The third case study is related with a convective th storm development event on June 16 in the central part of st FIG. 1: 500 mb Geopotential height and isotherm 2008 June 1 at the country. More than twenty millimeters precipitation in 00 UTC ten minutes and more than thirty five millimeters precipitation in one hour were collected. In the June 9-11th event, a cold pool in the high layers of the atmosphere (500 mb) is centered in the II. STUDY CASES southwest of the Iberian Peninsula favoring instability. In order to understand the development and Initially the temperature in the centre of the cold pool is -20 th th evolution of these severe weather situations, synoptic ºC. In June 9 evening and June 10 is filled and moves characteristics, mesoscale situation and other local slightly eastwards, maintaining the instability. In surface the meteorological characteristics are analyzed. In this study high pressures dominate, due to the 1031 mb Atlantic cases, we include datasets coming from the Basque Country anticyclone, centered at the southwest of Ireland, creating Automatic Weather Station Mesonetwork (see more details north component winds that provide humid air. th in Gaztelumendi et al., 2003), MSG and numerical The June 16 event is characterized by a through, in modelling. the 500 mb level, crossing from west to east the north of In the three studied events, there is instability in the Iberian Peninsula, the temperature at this level is around - high layers of the atmosphere. Two of them, (June 1st, June 18ºC. In surface a 1004 mb low pressure centre moves 9-11th) are situations characterized by a cold pool; joint to a rapidly over the Cantabric Sea. surface north wind providing humid air. The June 16th In the first episode of study, especially stands out the episode, the instability is generated by a through in the high large accumulated precipitations for the whole episode, due layers of the atmosphere. to the formation of a MCS. Up to six stations, all of them May the 30th, the cold pool locates in the centre of located in the surroundings of Bilbao, surpass the 120 mm the Iberian Peninsula, with a slight displacement toward the (see FIG 2), remarking 166.3 in the Deusto station (see FIG North in the 31st afternoon and June 1st evening. The 3). location of the cold pool generates a retrograde movement in the Basque Country with southeast winds in height; moving convective structures from the northeast of the Iberian Peninsula towards the Basque Country (see FIG 1). Another synoptic patterns point to the risks associated to this situation. There is convergence in the low levels of atmosphere that favor the upwards fluxes. In surface, a light north flux, due to a relative low pressure area located on the north of the Pyrenees, introduce humidity in surface. These factors could be able to generate mesoscale convective systems (MCSs) with unpredictable movements, and many times quasi-stationary situations when not exist unidirectional shear that can move easily the generated systems.

FIG. 2: Measured accumulated precipitation (mm) for 2008 May 31st and June 1st

291 5th European Conference on Severe Storms 12 - 16 October 2009 - Landshut - GERMANY

mm in 10 minutes were registered, this is a historic register (see table I and FIG 2 , 3, 4 and 5).

Max Max Station Date Station Date (10 min) (1 hour) Urkiola 23.6 2008/06/16 Urkiola 36.7 2008/06/16 Aixola 14.4 2008/06/16 Aixola 29.7 2008/06/16 Amorebieta 13.9 2008/06/10 Aitzu 27.3 2008/06/16 Elorrio 12.6 2008/06/16 Arkaute 26.2 2008/06/10 Aitzu 12 2008/06/16 Gardea 26 2008/06/10 st FIG. 3 Measured accumulated precipitation (mm) for 2008 June 1 Urkizu 12 2008/06/10 Deusto 19.6 2008/06/01 in Deusto-station LLodio 11.4 2008/06/10 Mungia 19.1 2008/06/01

During the second study case, different storms are TABLE I: Precipitation rate (in 1 hour and in 10 minutes) for some produced, causing hourly accumulated precipitations stations of the three study cases superior to 25 mm in the area. During the evening of June 10th in Gardea-station 26 mm/h are measured, during night The risk of convective precipitations episodes is in Arkaute-station 26 mm/h are registered (see FIG 4). higher in June, agreeing with the days of larger insolation. The formation of convective systems that produces theses episodes is favoured by relative low pressure areas, due to heat accumulation, in the centre of Iberian Peninsula and instability areas in the forward part of the troughs. These troughs usually affect the Iberian Peninsula with a north- south axis with south winds in height in the forward part. The topography and thermal instability also contribute to the creation, development and movement of convective cells. These troughs are created when the jet polar stream undulates and takes an accentuated north-south component, being able to generating an isolating process and strangulation of one part of this intense circulation (see FIG 1). These isolated patterns from the general circulation can generate a cold pool, i.e. a closed and isolated depression in height, which moves independently from general circulation, FIG. 4: Measured hourly maximum precipitation (mm) for 2008 can be stationary o even retrograde. This synoptic June 10th environment is favourable for Mesoscale Convective System generation. In the last episode, a very strong storm produces a 10-minute register of 23.6 mm in Urkiola-station, that turn IV. AKNOWLEDGMENTS into 36.7 mm in one hour. In other stations, severe storms The authors would like to thank Basque are observed; leaving hourly registers of 29.7 mm in Aixola- Government and specially Meteorology and Climatology station and 27.3 mm in Aitzu (see FIG 5). Directorate staff for public provision of data from Basque Country Automatic Weather Station Network. We also want to thank rest of our colleagues from Basque Meteorology Agency involved in the elaboration of severe weather episodes reports.

V. REFERENCES Egaña, J., S. Gaztelumendi, I.R. Gelpi, K.Otxoa de Alda, 2007: “A preliminary analysis of summer severe storms in the Basque Country area: synoptic characteristics”. ECSS 2007. Egaña, J., S. Gaztelumendi, I. R. Gelpi, K. Otxoa de Alda, 2007: “Synoptic patterns associated to severe storms in the Basque Country”. 7th EMS 8th ECAM. Gaztelumendi, S. Otxoa de Alda, K. Hernandez, R. 2003: “Some aspects on the operative use of the automatic FIG. 5: Measured hourly maximum precipitation (mm) for 2008 stations network of the basque country” III ICEAWS. June 16th Maddox, R. A., 1980: Mesoscale convective complexes. Bull. Amer. Meteor. Soc., 61, 1374–1387. III. RESULTS AND CONCLUSIONS Medina, M.. 1976: Meteorología básica sinóptica. Editorial The registered quantities of precipitation in the three st Paraninfo, 320 pp. events are very remarkable. In the June 1 event, is worth Martín León, F. Las gotas frías/ Danas ideas y conceptos. pointing out the accumulated data in the Bilbao City Servicio de Técnicas de Análisis y Predicción, INM. surroundings, 166.3 mm in Deusto station and 143.1 mm in Zipser, E. J., 1982: Use of a conceptual model of the life Llodio station in the whole episode. In the two other events, cycle of mesoscale convective systems to improve very- object of this study, the episode accumulations are not so short-range forecasts. Nowcasting, K. Browning, Ed., important; nevertheless the hourly intensities are superior in Academic Press, 191–204. some stations. In Urkiola station 36.7 mm in 1 hour and 23.6

292 5th European Conference on Severe Storms 12 - 16 October 2009 - Landshut - GERMANY

High resolution X-band Doppler radar observation of misocyclones along the convergence line.

∗ Hanako Y. Inoue1) , Kenichi Kusunoki1), Wataru Mashiko1), Syugo Hayashi1), Hiroshi Yamauchi1) Wataru Kato2), Keiji Araki3), Kotaro Bessho1), Shunsuke Hoshino1), Masahisa Nakazato1), Osamu Suzuki1) Toshiaki Imai3), Yasuhiro Hono2), Tetsuya Takemi4), Takaaki Fukuhara3), and Toru Shibata3) 1 Meteorological Research Institute, Tsukuba, Japan 2 East Japan Railway Company, Saitama, Japan 3 Railway Technical Research Institute, Tokyo, Japan and 4 Disaster Prevention Research Institute, Kyoto University, Kyoto, Japan (Dated: September 15, 2009)

I. INTRODUCTION MRI radar) was also installed at the roof top of Shonai airport during 2007 winter. MRI radar was operated in a multi PPI Tornado occurrence on the Japan Sea side in Japan is char- and RHI mode to observe the three dimensional structure of acterized by the winter-monsoon tornadoes associated with the storms. cold air outbreaks over the warm sea surface. Since win- We also used the surface observational data at 26 automated ter monsoon tornadoes can cause considerable damage in the weather stations, which were installed at 4-km interval for the Japan Sea coastal region, where the population is concen- Shonai Area Railroad Weather Project. trated, it is important to reveal their detailed structure and their mechanisms of generation and evolutions in order to prevent and mitigate wind disasters in this region. As part of a III. SYNOPTIC SITUATION research project for the development of an automatic strong gust detection system for railroads, the Shonai Area Railroad On December 31, 2007, an upper-cold vortex was over the Weather Project, field observation is being conducted in the north of the Japan Sea and the surface pressure pattern showed Shonai area, Japan, to study the fine-scale structure and time east-west pressure gradient, which is typical of winter mon- evolution of strong gusts in the Japan Sea coastal region in soon situation around Japan. A cold-air outbreak from the winter. The initial survey showed that most of the surface Eurasian continent over the warm sea surface continued and gusts observed in 2007 winter was associated with the upper the SW-NE oriented transverse mode snowbands, which ex- vortex signatures in the Doppler radar observations (Kusunoki tended perpendicular to the mean wind direction and nearly et al., 2009). Among these events, this paper presents the parallel to the coastline, were observed around the Shonai gusty event associated with the misocyclones along the con- area. vergence line on 31 December, 2007, under winter monsoon Associated with the passage of low-level trough, a well- situation, and focused on the characteristics and temporal evo- developed transversal snowband passed over the observational lution of the misocyclones. area around 04 LST (LST = UTC + 9 hours), which corresponded to the time of the surface gust observation. Wind profiler observation of Sakata Weather Station of II. DATA, OBSERVATIONAL AREA AND INSTRUMENTS JMA showed that while northwesterly to westerly prevailed below 2km MSL during the cold-air outbreak, southwesterly was observed before the passage of the intense snowbands The major facilities for the observation are two X-band (not shown). Doppler radars and automated surface weather transmitters. X-band Doppler radar of East Japan Railway Company (hereafter JR-EAST radar) was installed at Amarume Station, Ya- IV. OBSERVED SURFACE WIND GUST AND THE magata Prefecture, Japan, in order to assess the utility of MISOCYCLONES Doppler radar for the use in operational railroad warning sys-

tems (Kato, 2007). Since JR-EAST radar is needed to observe −1 wind gusts successively, it is operated in a single PPI mode Strong surface gust of 25.0 m s was observed around of 2rpm at the lowest elevation angle of 3.0 degree so as to 0405 LST at one of the automated weather station near the provide the reﬂectivity and Doppler velocity ﬁelds as close to coast (B1, Fig. 1). Associated with the increase of wind the ground as possible. A series of PPI scans taken every 30 speed, sudden change of wind direction (from SW to NW) seconds provides unique datasets to document temporal and and the pressure dip was also observed, whereas the temper- spatial variations of low-level circulation. X-band Doppler ature showed little variation. It is indicated that the observed radar of Meteorological Research Institute (MRI) (hereafter gust occurred at the wind shear line between southwesterly and northwesterly. The Doppler radar observation also showed that this intense transversal snowband was formed between the southwesterly [∗] Corresponding author: Hanako Y. Inoue, Meteorological Research Insti- and the following northwesterly, indicating distinct horizontal − − − − tute, 1-1 Nagamine, Tsukuba, Japan. e-mail: [email protected] shear (∼ 10 3 s 1) and convergence (∼ 10 2 s 1) across it.

293 2

(m s−1) 27 −1 24 maximum wind speed was estimated to be 8.6 m s , maximum wind speed of about 21 −1 18 22.1 m s was estimated by adding the relatively large trans- 15 − 12 1 9 lational speed of 13.5 m s associated with the passage of 6 3 misocyclone 4 over B1 station. The estimated maximum wind 0 0355 0405 0415 speed was comparable to the observed surface gust. Since the (deg) (LST) E translational speed of the convective cloud during the cold-air NE wind direction N outbreaks is generally large, it is suggested that vortices of rel- NW W atively weak tangential velocities can cause wind gusts due to SW S their large translational velocity. SE E 0355 0405 0415 (LST) (hPa) (oC) 995 5 39˚ 39˚ 0405 : 33 LST 0405 : 33 LST 994 temperature 4 2 993 3 992 2 surface pressure 991 1 990 0 989 −1 0355 0405 0415 3 (LST) 38.9˚ 38.9˚ FIG. 1: Time history of maximum wind speed (top), wind direction 4 (bottom), temperature and relative humidity (bottom) at B1 station B1 B1 between 0355 to 0415 LST.

TABLE I: Characteristics of misocyclones 1-5 derived from JR- 5 km 5 km 38.8˚ 38.8˚ EAST radar data. Lifetime (T), averaged eastward and northward 139.7˚ 139.8˚ 139.9˚ 139.7˚ 139.8˚ 139.9˚ translational velocity (Vx,Vy) for each misocyclone are listed to- −28−24−20−16−12−8 −4 0 4 8 12 (m/s) 12 16 20 24 28 32 36 40 44 48 (dBZ) gether with minimum - maximum of diameter (D), tangential veloc- FIG. 2: Doppler velocity (left) and radar reflectivity (right) of JR- ity (Vt) and vertical vorticity (Vor). EAST radar at 0405:33 LST. The detected misocyclones are shown by the circles. Wind barbs measured at automated weather stations 1 2 3 4 5 −1 are also depicted (one barb denotes 5 m s ). T (seconds) 350 903 670 1048 146 −1 Vx (ms ) 14.0 13.9 12.7 12.3 17.4 −1 Vy (ms ) 0.5 -1.0 -0.3 -0.6 2.3 D (m) 300-2100 300-2900 600-2100 200-1800 400-1500 V. SUMMARY −1 Vt (ms ) 4.7-8.7 6.3-8.5 7.1-9.5 7.0-10.9 6.7-8.5 −1 Vor (s ) 0.01-0.09 0.01-0.12 0.01-0.06 0.02-0.16 0.02-0.07 During the cold air outbreak, gusty wind was observed at one of the surface automated weather stations on 31 Dec, 2007 in the Shonai area, Japan. The observed gust corresponded to Within the transversal snowband along this convergence line, the passage of one of the misocyclones within the transver- at least five cyclonic vortex signatures, which were referred sal snowbands, which was associated with the distinct conver- to as misocyclones for their smaller horizontal scales, were gence line. The temporal evolution of the misocyclones along ∼ observed by the JR-EAST radar with the separation of 4 the convergence line are discussed in the presentation. 9 km. Low-level reflectivity field showed a staircase pattern, likely due to the distortion of the snowband near individual misocyclones. VI. ACKNOWLEDGMENTS Detection of the misocyclones for each PPI scan of JR- EAST radar at every 30 seconds was performed manually by identifying Doppler velocity couplet of maximum and mini- This research is supported by the Program for Promoting mum and tracking the size and location of each misocyclone. Fundamental Transport Technology Research from the Japan Each misocyclone was labeled 1 to 5. The lifetime of each Railway Construction, Transport and Technology Agency misocyclone was 17 minutes at the longest. The diameter (JRTT). ranged from about 200 to 2900 m, the tangential velocity was 5 to 11 m s−1, and the estimated vertical vorticity was about − − − the orders of 10 2 to 10 1 s 1 (Table I). VII. REFERENCES The misocyclones extended to the height of about 2.5 km at the maximum and their diameters and tangential velocities did Kato W. , H. Suzuki, M. Shimamura, K. Kusunoki and T. not show much vertical variation with height. It is likely that Hayashi, 2007: The design and initial testing of an X-band the misocyclones associated with deeper convection extended Doppler radar for monitoring hazardous winds for railroad to the higher altitude. system. Proc., 33rd Conf. on Radar Meteorology, P13A.15. The time of misocyclone 4 passage over B1 station was Kusunoki, K. et al., 2009: Wind gust and storm evolutions consistent with that of surface gust observation (Fig. 2). Al- observed during the Shonai Area Railroad Weather Project: A though the tangential velocity of misocyclone 4 at that time preliminary survey. Proc., 5th ECSS, P09.16.

294 5th European Conference on Severe Storms 12 - 16 October 2009 - Landshut - GERMANY

VERY STRONG CONVECTION AT THE BALTIC COAST OF LITHUANIA ON 25 NOVEMBER 2008 Izolda Marcinonien÷

Lithuanian Hydrometeorological Service, Rudnios str. 6, LT-09300 Vilnius, Lithuania, [email protected] (Dated: 11 September 2009)

I. INTRODUCTION II. PHYSICAL PARAMETERS AND CONCEPTUAL MODEL According to Lithuanian criteria for meteorological phenomena, > 30 mm/12 h of snow and a snow cover >30 Combining satellite imagery and numerical model cm/12 h is named a catastrophic event. parameters leads to the right definition of conceptual model The case, which has being analysed and presented, is (CM). According to physical parameters of atmosphere an exceptional one for Lithuania. During the night of 25 (ECMWF data) and to satellite (MSG-2) information November 2008, 66 mm of snow precipitated in a resort city obtained, the presented situation was typical for Comma of Nida located on a narrow peninsula of the Curonian CM, which was connected with strong Rapid Cyclogenesis Lagoon. (RaCy) process. Initiation of deep moist convection can be connected to a favourable thermodynamic environment, created by large-scale flows, and sufficient lift, usually provided by mesoscale process (Doswell, 1987). Wind gusts and a thunderstorm confirmed the intensity of convection at the Baltic coast. The first appearance of deep convection happens in 66% of all cases at WV-Boundaries (Krennert T., Zwatz- Meise V., 2002). WV-Boundaries are connected to dry air.

FIG. 1: The location of catastrophic event (lat. E55°, long. N21°) on Lithuanian map.

During 12 h period, snowcover increased by 36 cm, thus totalling to 45 cm by the morning! It was the largest single snowfall in Lithuania ever measured and the biggest increment of snow cover (over 12 hours) since 1936. FIG. 3: WV image and PV1 18 UTC 24-11-2009; N-Nida city.

An upper level PV anomaly, with its associated lowered tropopause, overrunning a low-level baroclinic zone, induces a cyclonic circulation within the upper levels of the troposphere (Hoskins and others, 1985).

FIG. 2: Monthly precipitation distribution in Nida, November 2008; FIG. 4: IR image, PVA on 500 hPa, AT1000 hPa and AT500 hPa, abscissa - days, ordinate - amount of precipitation (mm). 00 UTC, 25 Nov.

295 5th European Conference on Severe Storms 12 - 16 October 2009 - Landshut - GERMANY

FIG. 8: Nida in the morning after the event, 25 Nov.

III. SUMMARY

To conclude, the main features and reasons for development of this catastrophic phenomenon were:

FIG. 5: The location of cross-section inside the cloud spiral • Involuted cloud spiral as a result of RaCy action (METOP IR). was extended along the Baltic Sea – from Finland to Lithuania; • The “tail” of this cloud system had been discontinued and a new Comma cloud structure formed in cold air mass; • Deep intrusion of dry stratospheric air into lower levels of troposphere (PV=1 low down up to 500- 550 hPa); it lowered the level of tropopause; • Comma was in front of upper level trough and PVA max in left exit region of a jet streak; Obviously, it was not difficult to detect the formation of RaCy in advance, unfortunately, it was impossible to predict the magnitude of the phenomenon. Firstly, it was a local-scale event; secondly, during late autumn season heavy snow is very rare and unusual in western Lithuania. As regards the impact of this hazardous event, only a limited damage was caused to forestry and roads in and around Nida. FIG. 6: Isentropes (Theta E; black) and PVA (green), 18 UTC 24 Nov. Combination of convergence, cold dry air intrusion IV. ACKNOWLEDGMENTS from higher levels and mesoscale upward motion leads to The author is very grateful to her Austrian rapid cyclogenesis with convective activity at the rear and colleagues from the ZAMG Remote Sensing Division for within frontal cloud bands (Zwatz-Meise V. and Mahringer their help with satellite data and productive discussions G., 1990). In this case, a local-scale heavy snow was about this case study. formed. V. REFERENCES Doswell C. A., 1987: The distinction between large-scale and mesoscale contribution to severe convection: a case study . Weather&Forecasting, Vol. 2, p. 3-9.

Hoskins B. J., McIntyre M. E. and Robertson A. L. W., 1985: On the use and significance of isentropic potential vorticity maps; Quart. J. R. Meteor. Soc., Vol. 111, p. 877 – 946.

Krennert T., Zwatz-Meise V. Initiation of convective cells in relation to water vapour boundaries in satellite images. Atmos. Res., 67-68 353-366. Zwatz-Meise V. and Mahringer G., 1990: SATMOD: An interactive system combining satellite images and model output parameters; Weather&Forecasting, Vol. 5, p. 233 –

FIG. 7: Vertical motion (blue: Omega parameter), 18 UTC 24 Nov. 246.

296 5h European Conference on Severe Storms 12 - 16 October 2009 - Landshut - GERMANY

WIND GUST AND STORM EVOLUTIONS OBSERVED DURING THE SHONAI AREA RAILROAD WEATHER PROJECT: A PRELIMINARY SURVEY

Kenichi Kusunoki1, Hanako Inoue1, Wataru Mashiko1, Syugo Hayashi1, Wataru Kato2, Keiji Araki3, Kotaro Bessho1, Shunsuke Hoshino1, Masahisa Nakazato1, Toshiaki Imai3, Yoshihiro Hono2, Tetsuya Takemi4, Takaaki Fukuhara3, Toru Shibata3 1 2 Meteorological Research Institute, 1-1, Nagamine, Tsukuba 305-0052, Japan, [email protected], East Japan Railway Company, 2-479, Nisshin-cho, Kita-ku, Saitama 331-8513, Japan, [email protected] 3Railway Technical Research Institute, 2-8-38, Hikaricho, Kokubunji, Tokyo 185-8540, Japan, [email protected], 4Kyoto University, Gokanosyo, Uji, Kyoto Japan 611-0011, Japan, [email protected]

I. INTRODUCTION two X-band Doppler radars and the network of automated On Japan railroads, wind conditions affect operating weather station sites. efficiency, infrastructure, and safe passage of people and freight. For instance, strong and gusty winds cause regional 1) JR EAST X-band Doppler radar delays or shutdowns, and especially hazardous crosswinds JR EAST X-band Doppler radar was installed at the may lead to overturn of railcars. Since propeller-vane/cup Amarume station in Shonai Town since March 2007. Since anemometers densely cover on the railroads for operations it is needed to observe wind gusts successfully, the radar is through some wind speed thresholds (e.g., winds in excess of operated in a single PPI mode at the lowest elevation angle 25 ms-1), small-scale but strong gusty winds are difficult to possible to provide the reflectivity and Doppler velocities as detect with the present system. The Shonai area railroad close to the ground. The single elevation angle is 3.0 degree weather project will investigate fine-scale structure of wind and the scans are taken every 30sec (Kato et al. 2007). gust dynamics and kinetics such as tornadoes, downbursts, and gustfronts. The ultimate goal of the project is to develop 2) MRI portable X-band Doppler radar an automatic strong gust detection system for railroads, MRI portable X-band Doppler radar (X-POD: X-band, which the decision to warn is generally based upon POrtable Doppler radar) have been installed on the roof of information from a single-Doppler radar at low elevation Shonai Airport building since late December 2007 angles. In this presentation, we will introduce an overview of (Kusunoki and Ichiyama, 2007). The radar, in combination the project as well as highlights from the planned field with other devices such as the JR EAST X-band Doppler campaign and some initial results in the first winter of the radar, has been used to obtain detailed meteorological data project (1 October 2007 to 31 January 2008) will be in the Shonai area. The distance between these radars is presented. 10km and dual-Doppler scanning was conducted. The X-POD had a 2.5 minute-volume scan which was regularly interrupted by the RHI scans at the azimuth angles of 135

II. THE GOALS OF THE PROJECT and 315degrees. In order to develop an automatic strong gust detection system for railroads using a single-Doppler radar wind 3) Surface network of automated weather station sites observation, the following steps will be implemented: In order to characterize and validate these structures near 1) Research on fine-scale structure of strong gust and the surface, the surface weather stations were distributed in associated storm dynamics and kinetics. the study area. We have installed 26 weather transmitter 2) Assessment of radar performance for strong gust (WXT520; Vaisala) at intervals of 4 kilometers in the area detection. around the Shonai plain. Each device as been mounted on 3) Prototype implementation for future strong gust detection the top of a steel pole as high as 5 meters. The observation system for railroads. intervals are 1 second for wind direction and wind speed, and 10 seconds for temperature, humidity and pressure. The III. THE FIELD CAMPAIGN observation data are to be sent to the computer in the In the first phase of the project 1), fine-scale structure of Institute via the Internet. These observations provide a strong gusts over the Shonai Plain have been explored using detailed, high quality dataset with which to compare the the field campaigns and mesoscale simulations. simulation results. In addition to the above instruments, 60 GPS sondes were launched within 1-3 hours interval in the a. The study area study area in December 2008 to recognize the vertical The high-resolution observations of strong gust structures of strong gust conditions. The sonde soundings in phenomena have been performed over the Shonai area the study area will be performed in this winter. (Yamagata Pref., Japan). Primarily, over the Sea of Japan side, severe storms such as tornadoes and gust-generating IV. INITIAL RESULTS cold fronts occur frequency in winter season. The Shonai Wind gust events were selected based on surface wind area would provide an ideal setting for studying these speed data from the surface observation network. The phenomena (Kusunoki et al. 2007). following wind gust identification criteria were used at each surface wind data: b. Instrumentations (1)Vpeak >= 25ms-1, (2)DV >= 15ms-1, and (3) Major observing facilities for this project included the DT<=3minutes,

297 5h European Conference on Severe Storms 12 - 16 October 2009 - Landshut - GERMANY where Vpeak is the peak wind speed, DV is defined as the band Doppler radar for monitoring hazardous winds for difference between Vpeak and the average wind prior to the railroad system. Preprints, 33rd Conf. on Radar gust, and DT is the difference between the time of the peak Meteorology, Cairns, Australia, Amer. Meteor. Soc. wind speed and the beginning of increase of wind speed. P13A.15. Because it is not easy to determine the values of DV and Dt Kusunoki, K. and T. Ichiyama, 2007: The MRI portable from the surface wind speeds which contains turbulent X-band Doppler radar (X-POD): Status and fluctuations, the criteria 2 and 3 were manually identified. Applications. Preprints, 33rd Conf. on Radar The resultant wind gust dataset (ten cases) is described in Meteorology, Cairns, Australia, Amer. Meteor. Soc. Table 1. P13A.8. In each case, surface wind and surface pressure Kusunoki, K., T. Imai, H. Suzuki, T. Takemi, K. Bessho, M. observations confirmed the passage of a storm-scale vortex Nakazato, S. Hoshino, W. Mashiko, S. Hayashi, H. Inoue, over the surface observation site. There was a suggestion of T. Fukuhara, T. Shibata, W. Kato, 2008: An overview of storm-scale vortices within parent storms seen in the radar the Shonai area railroad weather project and early reflectivity and Doppler velocity data from the JR-East radar. outcomes Preprints, Fifth Conference on Radar Figure 1 shows examples of wind gust characteristics. In the Meteorology and Hydrology, Helsinki, 30 June - 4 July, case of 5 December 2007, surface observation site C4 2008. P12.1. -1 confirmed a maximum wind of 28.2 ms . Over the same time, 360 the wind direction changed from the west-southwest to the Observation Site C4 (a) northwest and the surface pressure dropped about 2hPa. Almost simultaneously, JR-E radar revealed that the Wind direction 300 existence of mesoscale vortices and hook echoes. direction Wind

Surface Time Wind speed Parent storm Date observatio 24035 1021 (LST) (ms-1) type n site

) 30

-1 15 November 2007 A1 10:46:29 26.2 CL Surface pressure 18 November 2007 E1 8:12:48 27.5 T 25 1020 19 November 2007 SAK 5:06:30 25.6 T->L 20 19 November 2007 A1 5:46:49 25.8 T->L 15 05 December 2007 C4 8:42:04 28.2 C speed(ms Wind 30 December 2007 B1 18:57:53 26.1 T 1019 10 (hPa) Surface pressure 31 December 2007 B1 4:05:50 25 T Wind speed 1 January 2008 B1 13:27:28 29 T->L 5 17 January 2008 B1 11:34:52 25.1 C 0 1018 25 January 2008 C2 5:27:41 31.3 L 8:38:00 8:39:00 8:40:00 8:41:00 8:42:00 8:43:00 8:44:00 8:45:00 8:46:00 25 January 2008 SHO 5:28:42 28.8 L Time (LST)

TABLE 1. Wind gust dataset during the first winter of the project (1 (b) October 2007 to 31 January 2008). T, L, CL, and C refer to parent storm of transverse (wind-normal) cloud bands, longitudinal (wind-parallel) cloud bands, convective line and cell, respectively.

V. CONCLUSIONS AND FUTURE WORK In this presentation, we briefly present some initial results from the gust wind dataset during in the first winter of the project (1 October 2007 to 31 January 2008). High-resolution observations obtained with the JR-E radar revealed that the existence of mesoscale vortices and hook 0 2km 0 2km echoes. Surface observation network confirmed wind gusts associated with the passage of these vortices. On wind gust detection, one of the paramount features is a tornado and/or a larger circulation within which tornadoes are expected to occur. Therefore, these results are noticeable and will assess FIG. 1 Examples of wind gust characteristics observed during the project. (a) Surface wind speeds, directions, and surface pressures of Doppler radar performance for gust wind detection. at the surface observation site C4. The vertical hatch is indicated Because it is premature to extrapolate our results from this by the radar scanning period of (b). (b) Radar reflectivity on 5 one winter season, additional gust cases are needed to December 2007, at 08:41:40 LST just before the passage of a confirm this preliminary study. radar vortex pattern over the surface observation site C4. Data were collected by the JR-East X-band radar. The surface VI. AKNOWLEDGMENTS observation site C4 is indicated with a plus sign. This study was supported by the Program for Promoting Fundamental Transport Technology Research from the Japan Railway Construction, Transport and Technology Agency (JRTT).

VII. REFERENCES Kato, W., H. Suzuki, M. Shimamura, K. Kusunoki, and T. Hayashi, 2007: The design and initial testing of an X-

298 5h European Conference on Severe Storms 12 - 16 October 2009 - Landshut - GERMANY

A CASE STUDY OF SEVERE CONVECTION OVER CENTRAL EUROPE WITH THE DETAILED ANALYSIS OF DEVELOPMENT OVER CROATIA ON 22ND AND 23RD JUNE 2007 Dunja Plačko-Vršnak1, Nataša Strelec Mahović1 1Meteorological and Hydrological Service, Gric 3, Croatia, [email protected], [email protected] (Dated: 15 September 2009)

I. INTRODUCTION

Thunderstorms belong to the short-living weather phenomena. Due to the associated risk of damage caused by lightning, heavy rainfall or hail they are of great interest to the customers. A precise forecast of convection is therefore one of the most important tasks for the forecasters. Remote sensing data combined with synoptic information give the opportunity to monitor the relevant developments, especially for nowcasting purposes. This study deals with a case of severe convective development over Central Europe which happened from 21st to 23rd June 2007. Large areas of Germany, Austria, Czech Republic and Croatia were affected by heavy thunderstorms. Hail and wind bursts killed several people and caused damage in millions of Euros. FIG. 2: Radar reflectivity in dBz for 23 June, 00 UTC – strong convection over the central and north Croatia with reflectivity over II. THE CASE – ANALYSIS OF CONVECTIVE 55 dBz - hail occurrence is highly probable. DEVELOPMENT OVER CROATIA

In the strong SW flow over Croatia the humid and warm air was coming from the West Mediterranean in front of the cold front. Strong convective activity occurred during the night of the 22nd in the coastal regions of the North Adriatic and during the early morning of the 23rd in the central and north-east part of Croatia (FIG. 1). Convection was triggered by the orography and the passage of the cold front. The atmosphere over Croatia was very unstable. Forecast values of Showalter index over the central parts of Croatia were below -3 (FIG. 3). This high instability resulted in the development of many convective cells with radar reflectivity up to 55 dBz (FIG. 2). The convection over the central Croatia had rather good fit with the model.

FIG. 3: Showalter index (ALADIN/HR model) valid for 23 June, 00 UTC. Values under -3 – heavy thunderstorms is highly probable.

III. NOWCASTING PRODUCTS

Several nowcasting products based on satellite data were used in detailed analysis of convective development and movement of the cells over Croatia. One of them is the cloud motion vector product, combined with forecast cloud contours overlaid on the Meteosat 8 IR 10.8 µm image. Expected displacement of the cloud feature within 1 hour time period in the strong westerly flow is shown in FIG. 4. Isolines delineating the area of different cloud top temperature (inner with temperature lower then -60 °C) have a good forecast value during severe convective development over the north and north-east Croatia, and further to the

east. FIG. 1: Meteosat 8 IR 10.8 image for 23 June, 00 UTC - developing convective cells over the central and east Croatia.

299 5h European Conference on Severe Storms 12 - 16 October 2009 - Landshut - GERMANY

V. AKNOWLEDGMENTS (TIMES NEW ROMAN 10-BOLD CENTRE JUSTIFIED CAPITAL)

The case study was performed under the framework of the EUMeTrain project. (http://www.zamg.ac.at/eumetrain)

VI. REFERENCES (TIMES NEW ROMAN 10-BOLD CENTRE JUSTIFIED CAPITAL) Schipper J., Placko-Vrsnak D., Jacobs W., 2008: Case Study on severe convection over Central Europe. EUMeTrain, http://www.zamg.ac.at/eumetrain FIG. 4: Meteosat 8 IR 10.8 image for 23 June, 00 UTC overlaid Setvak M. et al., 2008: Cold-ring shaped storms in Central with cloud motion vectors and forecast cloud contours. Europe. 2008 EUMETSAT Meteorological Satellite

Conference, Proceedings (http://www.eumetsat.int). Temperature enhancement of Meteosat 8 IR 10.8 µm image resolves the temperature of the cloud tops in more Strelec Mahović N., 2005: Operational use of Meteosat 8 detail and helps discriminating different cloud-top features. SEVIRI data and derived nowcasting products. 2005 This enables the study of the cloud features like cold-U EUMETSAT Meteorological Satellite Conference, shape and cold-ring shape which can be the indicators of Proceedings (http://www.eumetsat.int). storm severity (Setvak et al, 2008). In FIG. 5 the majority of severe convection moved from the east Croatia to the north Serbia where a well- defined cold-ring feature (marked with an arrow) can be seen.

FIG. 5: Meteosat 8 IR 10.8 enhanced image for 23 June, 01 UTC . Cold-ring feature marked with an arrow.

IV. SUMMARY

Convective development over Croatia was only a part of heavy convection episode which happened from 21st to 23rd June in large part of central Europe. The north part of Adriatic coast and some parts of the inland of Croatia were devastated by severe storm accompanied by hail. Strong convective activity started ahead of the cold front, induced by orography. The atmosphere was very unstable. That can be seen in the numerical fields of stability indices as well as in radar and satellite images. On the smaller scale convective development was followed by using some nowcasting products based on satellite data. Severe convective development over some parts of Croatia was well witnessed also by using colour enhanced infrared 10.8 µm images.

300 5th European Conference on Severe Storms 12 - 16 October 2009 - Landshut - GERMANY

DERECHO ON 25TH OF JUNE 2008 Tomáš Púčik1, Martina Francová2, David Rýva3, Miroslav Kolář1

1 Faculty of Science, Masaryk University Brno, Czech Republic, [email protected] 2 Czech Hydrometeorological Institute, Praha, Czech Republic 3 Skywarn Czechoslovakia, Czech Republic

(Dated: 15 September 2009)

I. INTRODUCTION risk of tornadoes and severe wind gusts. Derechos are known as “widespread, convectively induced windstorms” and have been known as prolific wind damage III. REMOTE SENSING, VISUAL producers. The criteria for derechos can be found in (Johns OBSERVATIONS AND MEASUREMENTS OF and Hirt, 1987). Most of these phenomena are linked to the WEATHER STATIONS organised storm systems attaining the characteristic of “bow A line of isolated cells, including supercells, formed over echoes”, their structure and flow is described for example in Germany and western Bohemia and progressed eastwards (Weisman, 2000). Bow echoes and supercells arise in similar around 14:00 UTC. Storm coverage grew quickly with the conditions, often with strong deep layer shear and high merging of the cold pools of individual storms. The storm instability (Evans, J. S., and C. A. Doswell III, 2001:), but system attained a linear shape and developed into a squall some differences have been found, such as in (Doswell, C. A. III, and J. S. Evans, 2003). On 25th of June 2008, line shortly before 16:00 UTC. In the mean time, moist air, with dew points exceeding 20°C, was spreading northward a widespread, convectively induced windstorm travelled from Austria into Eastern Bohemia. Ahead of the storm across most of the Czech republic and affected several other system, two isolated supercells were observed and countries as well. The windstorm was mostly the result of extensively documented by local storm spotters. the formation of two bow echo systems. Apart from the straight-line wind damage, an F2 tornado also occurred. Several supercells have been observed on this day as well. The main three goals of this case study is to 1/ Evaluate the environmental conditions in relation to the supercell and bow echo development. 2/ Compare the remote sensing, visual observations and measurements of weather stations. 3/ Make a detailed damage analysis and make an inspection of its relation to the mesoscale structures within the bow echo.

II. SYNOPTIC-SCALE AND MESOSCALE ENVIRONMENTAL CONDITIONS th On 25 of June 2008 a prevailing zonal flow was present FIG. 1: Supercell above north eastern Bohemia, 15:25 UTC with several disturbances, notably a short-wave trough over the Eastern Atlantic and a ridge passing over Central Radar signatures such as hook echoes were Europe. A strong westerly-northwesterly upper-level jet observed with these storms. At the same time a mesolow stream crossed the northern part of a warm sector with high formed in this area at 17:00 UTC with enhanced theta-e values across central Europe. At the surface, a convergence of very moist air ahead of the progressing shallow trough emerged from a surface low centered over system. In this region, the squall line gained characteristics Great Britain. A significant frontal system developed, its of a bow echo. warm front slowly progressing to the northeast across Germany and Poland with warm and moist air mass (dew points locally over 20°C) being advected behind it. Significant destabilization occurred during the daytime hours in this air mass as shown by 12 UTC soundings from Germany and the Czech Republic. Strong, mostly unidirectional wind shear was present, with values over 20 m/s in the 0 – 6 km layer. Above the level of approximately 500 hPa winds did not increase at all, or even weakened, implying rather weak storm relative winds in the upper troposphere. Backing low level winds and enhanced SREH along the frontal boundary FIG. 2: Radar PPI 0.9° captions of the storm development. Left: were simulated by several numerical models. SREH values bow echo stage. Right: Isolated supercell with hook echo (a photo of increased ahead of the amplifying trough towards the it can be found in Figure 1) evening and models simulated over 300 J/kg across the 0-3 A clear bow apex and rear inflow notch were km layer in eastern Bohemia. At the same time, low level observed. The bow echo attained considerable forward shear increased with values up to 20 m/s across the 0-3 km speed, approaching 100 km/h, soon engulfing two isolated layer and over 10 m/s across the 0-1 km layer, implying a

301 5th European Conference on Severe Storms 12 - 16 October 2009 - Landshut - GERMANY supercells. The wind damage was most prolific during the That is the reason why we finally agreed that most damage “bowing stage” with several stations reporting gusts above was caused by numerous strong F2-F3 microbursts. But 32 m/s. A northern book-end vortex became dominant thanks to the eyewitnesses and some local tornadic damage, during this process. we are sure there was one or more tornadoes of F2 intensity At 18:00 UTC, approximately one hour after the as well. Some very local damage also seemed to be caused passage of the gust front, a sounding from Prague-Libus by suction vortices. It seems that the most severe damage showed a very strong Rear Inflow Jet (RIJ) at an altitude of and a tornado had occurred on the northern half of the bow about 3 km ASL with a maximum speed over 35 m/s. Rear visible in Figure 2, with possible enhancement due to the Inflow Jets are characteristic of bow echoes and play a major merger of the supercell and bow echo, embedding the role in the wind potential of these systems (Wakimoto, circulation of the supercell in the system. 2001). The Front to rear and the Rear Inflow Jet have also been derived from the VAD radar analysis with the radar at Brdy. A significant meso-high developed in the wake of the gust front, with pressure differences of 7 hPa across a very small distance, which likely contributed to the severe wind gusts. On PPI scans of low elevations, LEWP structures were evident, suggesting that embedded circulations might have been present. Later on, after 19:00 UTC the bow echo had turned into a shape of “comma echo”, described in e.g. (Fujita, 1979).

FIG. 5: Most trees fell down eastwards, the same direction as the whole system moved.

V. REFERENCES

Doswell, C. A. III, and J. S. Evans, 2003: Proximity sounding analysis for derechos and supercells: An assessment of similarities and differences. Atmos. Research, 67-68, 117-133. FIG. 3: VAD profile of the Radar at Brdy before and after the passage of the gust front (red crosses stand for 13,4° elevation and Evans, J. S., and C. A. Doswell III, 2001: Examination of orange for 34,3°) at 16:14 and 16:54 overlaid with 12 UTC sounding measurements from Prague and Prostejov (light and dark derecho environments using proximity soundings. Wea. blue lines respectively). Forecasting, 16, 329-342. Fujita, T. T., 1978: Manual of downburst identification for IV. DAMAGE ANALYSIS project Nimrod. Satellite and Mesometeorology Research The first reports from the media and public showed Paper 156, Dept. of Geophysical Sciences, University of extensive wind damage, mainly in the eastern part of Chicago, 104 pp. Bohemia. An in-situ survey showed even more than we Gatzen, C., 2004: A derecho in Europe: Berlin, 10 July could have imagined. The first presumption was the F-3 2002. Wea. Forecasting, 19, 639-645. tornado, 100 – 300 m wide. Eyewitnesses described a tornado, and we also found typical damages which could not Johns, R. H., and W. D. Hirt, 1987: Derechos: widespread have been caused by anything else than a tornado. convectively induced windstorms. Wea. Forecasting, 2, 32- 49.

Punkka, A-J., and J. Teittinen, 2004: The severe thunderstorm outbreak in Finland on 5 July 2002. Preprints, 22nd Conf. on Severe Local Storms, Hyannis, MA, Amer. Meteor. Soc, Paper P4.9, 7 pp.

Wakimoto, R. M. 2001: Convectively driven high wind events. Severe Convective Storms, Meteor. Monogr., No. 50, Amer. Meteor. Soc., 255-298. Weisman, M. L., 1993: The genesis of severe, long-lived bow echoes. J. Atmos.Sci., 50, 646-670 Weisman, M. L., 2001: Bow echoes: A tribute of T. T. FIG. 4: The arrow shows the area with the largest damage. Fujita. Bull. Amer. Meteor. Soc., 82, 97-116. Thanks to our collaborators among amateur storm chasers we obtained air photos, which helped the most to decide what had happened there. On these photos it can be seen that most trees fell eastwards, the same direction as the whole system. If it had been a tornado, trees would have fallen in various directions, suggestive of tornado rotation. 302 5th European Conference on Severe Storms 12 - 16 October 2009 - Landshut - GERMANY

CASE STUDY OF SEVERE WINDSTORM OVER SLOVAKIA AND HUNGARY ON 25 JUNE 2008 André Simon1, Ján Kaňák2, Alois Sokol3, Mária Putsay1, Lucia Uhrínová2 and Kálmán Csirmaz1

1Hungarian Meteorological Service, Kitaibel Pál u. 1, H-1024, Budapest, Hungary, e-mail: [email protected] 2 Slovak Hydrometeorological Institute, Jeséniova 17, 833 15 Bratislava, Slovakia, e-mail: [email protected] 3 Comenius University, DAPEM FMPI CU, Mlynská dolina F1, 842 48 Bratislava, Slovakia, [email protected] (Dated: 15 September 2009)

I. INTRODUCTION was relatively buoyant at mid-troposphere with low to A large system of thunderstorms, which developed moderate total precipitable water content (Fig. 1). About 16 near a cold front, passed through several central European UTC the convective activity was concentrated over Bavaria, countries on 25 June 2008. Heavy rainfall, hail and severe northern and western part of Czech Republic, where the wind gusts were reported from several places in Slovakia thunderstorms formed into a line propagating and Hungary. The wind gust peak measured at Bratislava southeastwards. At the same time a cluster of thunderstorms Ivanka airport reached 40 m/s and material damages were started to develop over the Alps in Austria. The 10.8 µm IR caused by wind in Bratislava, Senec and other districts, channel shows the evolution of cold U- and V-shapes in mostly in the west and southwest of Slovakia. Condensation cloud-top temperature field between 1810 and 2200 UTC in clouds (probably wall clouds or funnel clouds) were this cluster over the north of Austria, while the convection in observed and photographed at Blahová, in the south of the northern part of the cold front seems to become weaker. Slovakia. The windstorm was weaker over Hungary, however, wind gusts up to 25 m/s were measured at Bakony hills (at the meteorological station Kab-hegy) and at lake Balaton. According to SYNOP observations and other weather reports from Austria, Czech Republic and Germany the weather event had some characteristics of a derecho.

II. SYNOPTIC OVERVIEW Thunderstorm clouds were present already in the morning hours of 25 June 2008 over the east of France and the west of Germany in the area of large, but shallow surface trough, which slowly propagated eastward. At 12 UTC convective systems developed close to the surface convergence zones over the east and central part of Germany. In the afternoon further development of deep convection can be associated with cold front over Bavaria. At 18 UTC this front was over the middle part of Czech Republic and Austria. According to soundings and ECMWF analysis and forecasts there was a southerly advection of pre-frontal warm air, which caused a buoyancy increase at middle- and upper levels. The Prague sounding at that time FIG. 1: The composite image of MSG IR 10.8µm channel (over shows a significant increase of low-level wind speed (25 m/s cloudy areas) and derived (GII) product of total precipitable water content field (over clear areas) at 1915 UTC. The arrows mark the westerly wind at 850 hPa) behind the front. The convective position of the highest wind gusts measured in Slovakia and system entered the territory of Slovakia and Hungary after Hungary. 20 UTC. At the same time it was possible to observe high surface pressure gradient (more than 4 hPa/100 km), which The column maximum radar reflectivity of the developed between the high pressure region over northern cells propagating from Czech Republic and Moravia Austria and lower pressure over the southwest of Slovakia significantly decreased from 55 dBZ to 40-45 dBZ after and the north of Hungary. On 26 June 2008 00 UTC the cold 1930 UTC. Both systems merged together and new front reached the area of central Slovakia and Hungary. The thunderstorm cells appeared over the southwest of Slovakia intensity of the convective system decreased in the morning and the northwest of Hungary after 2100 UTC. Bow echoes hours of 26 June 2008 over eastern part of Slovakia and and line echo wave patterns could be observed. At some Hungary. stages the radar reflectivity images show a chain of relatively independent cells developing along the leading III. SATELLITE AND RADAR OBSERVATIONS edge of the convective system. Strong lightning activity, The mesoscale conditions for thunderstorm evolution heavy rain and severe wind occurred also in the rear side of can be documented by Meteosat Second Generation (MSG) the system, where the radar reflectivity was weaker (e.g. the imagery and convective indices (GII) inferred from satellite highest wind gust at Bratislava was measured at 2138 UTC data. The indices show that the pre-frontal, cloud-free air nearly 50 km behind the line of the heaviest thunderstorms).

303 5th European Conference on Severe Storms 12 - 16 October 2009 - Landshut - GERMANY

with the conceptual model of mesovortices. Similar vortices develop also in model runs with different parameterisation of turbulent fluxes (Eta PBL or MRF PBL closure schemes) or by higher (1.5 km) resolution. On the other hand, in WRF simulation the strong low-level wind is rather related to high pressure gradient along the cold front line, which is of larger scale than by the MM5 simulation. It is important to note that the above mentioned model runs did not forecast the decrease of mid-level cloud water quantity or simulated radar reflectivity, which were observed by radars.

V. CONCLUSION Forecasters usually pay high attention to large- scale convective systems connected with cold fronts and convergence lines, which can be nowadays well detected and forecasted several hours in advance. Nevertheless, some features (e.g. temporal decrease of radar reflectivity) can be sometimes misleading in predicting the system intensity and severity. Numerical simulations indicate that severe FIG. 2: Forecast of vorticity (color, 10-5 s-1), vorticity tilting term windstorms similar to the 25 June 2008 case can arise from (lines, 10-7 s-2) and storm relative wind (barbs, m/s) at 3 km height in several reasons. Except of downdrafts and convective MM5 run based on 25 June 2008 06 UTC, valid for 2055 UTC. outflows or large scale pressure gradient flow, low level wind can be enhanced in the rear flank of meso-gamma scale vortices embedded in the system. The detection (verification) of such mesovortices is rather difficult. Radar doppler velocity simulated by MM5 model shows that such objects do not always exhibit a significant MVS (Mesocyclone Vortex Signature) pattern because their vorticity is usually weaker than the vorticity of supercell mesocyclones. Thus, forecasts of high-resolution numerical models can be very useful in specifying the character and intensity of the event, though their results are not perfect and depend on many factors (boundary conditions, parameterisation of microphysics, etc.). Satellite observations and derived parameters provide further useful information about the buoyancy and humidity distribution in the pre-frontal airmass that can help to specify the potential for severe convective storms development.

VI. ACKNOWLEDGEMENTS FIG. 3: Hodographs of storm relative wind derived from MM5 The authors would like to thank Mr. Tibor Csörgei forecast at points 1 and 2 (Fig. 2). The density-weighted wind over and Mr. Tibor Szalay for photographs and description of their observation. Part of this research was supported by 0-6 km layer was considered as “storm motion” vector (v1 and v2). Hungarian National Program for Research and Development IV. NUMERICAL SIMULATIONS (NKFP, project number 3/0022/2005). The numerical models MM5 (Dudhia, 1993) and WRF (Skamarock et al., 2008) were integrated at 3 km VII. REFERENCES horizontal resolution using non-hydrostatic dynamics. Both models were coupled by ECMWF boundary and lateral Dudhia, J., 1993: A Nonhydrostatic Version of the Penn conditions. Several setups of physical parameterization State-NCAR Mesoscale Model: Validation Tests and (turbulent fluxes, microphysics) were tested. The operational Simulation of an Atlantic Cyclone and Cold Front. Mon. version of the MM5 model based on the 25 June 2008 06 Wea. Rev., 121 1493-1513. UTC run successfully forecasted several mesoscale features mentioned in sections above (e.g. the merger of two Skamarock, W. C., Klemp, J. B., Dudhia, J., Gill, D. O. , convective systems, wind gust peak in the Bratislava region, Barker, D. M., Duda, M., Huang, X.-Y., Wang, W. and J. etc.). The forecasted system consisted of several, rapidly G. Powers, 2008: A Description of the Advanced Research developing cells. Some of them were marked by significant WRF Version 3, NCAR Technical Note, NCAR mid- and low-level vorticity (0.003 s-1), moderate updrafts TN475+STR, 113 pp. (10 ms-1) but relatively weak downdrafts (only few ms-1). The low-level wind was enhanced in the rear side of these Weisman, M. L., Trapp, R. J., 2003: Low-Level cells as a consequence of locally increased pressure gradient. Mesovortices within Squall Lines and Bow Echoes. Part I: The structure of the cells is more similar to meso-gamma Overview and Dependence on Environmental Shear, scale vortices (Weisman and Trapp, 2003) than to classic or Mon. Wea. Rev., 131 2779-2803. HP supercell. The mid- level vorticity originates mostly from the crosswise vorticity tilting (Fig. 2) that also agree

304 5h European Conference on Severe Storms 12 - 16 October 2009 - Landshut - GERMANY

EXAMINATION OF TWO SEVERE THUNDERSTORM EVENTS IN SOUTHERN GERMANY Helge Tuschy1,2,3, Martin Hagen1, Georg J. Mayr2 1Deutsches Zentrum für Luft- und Raumfahrt (DLR), Institute für Physik der Atmosphäre (IPA), Oberpfaffenhofen, Germany, [email protected] 2 Leopold-Franzens University, Innsbruck, Austria 3 European Severe Storms Laboratory, ESSL

I. INTRODUCTION

Various severe thunderstorm events affected central Europe in the past few years. Some occurred in the typical environment of strong wind shear and high instability, where long-lived and organized thunderstorms are common. Others developed in an environment, where both the behavior and the strength of those thunderstorms were not expected. Two case studies will be discussed on the poster, one of a severe hailstorm and another one of a bow echo event over southern Germany. The information about the behavior of those thunderstorms was gathered by a combination of the polarization diversity Doppler radar (POLDIRAD) at DLR, Oberpfaffenhofen, the high resolution weather forecast model data from the DWD (COSMO-DE, horizontal mesh grid width is 2.8 km) and remote sensing data.

II. PRESENTATION OF RESEARCH FIG. 1: Comparison between COSMO-DE and POLDIRAD. The PPI (colorbar) and COSMO-DE output (area, shaded in Two case studies are discussed on the poster. First a severe dark red) are from 1510 UTC. In COSMO-DE, reflectivity hailstorm over southeast Germany on 22 August 2008 and values less than 40 dBZ were cut off. then a severe bow echo over southern Germany on 26 May 2009. The first point of study was the occurrence of typical bounded weak echo region. This thunderstorm was a patterns on radar, like the three-body scatter spike, the powerful hail producer with the hail core being tracked chronological evolution of an hail core and the signatures of throughout the most serious phase of this supercell by a mature bow echo, like a rear inflow notch. It was of different polarimetric measurements of POLDIRAD. interest to understand the mechanisms, that resulted in a Despite the more unidirectional wind shear, the increasingly symmetric, progressive bow echo event. In that event, deviant storm motion to the right of the 0-6 km background another point of interest was the performance of the bulk wind speed shear vector caused storm relative helicity COSMO-DE in this situation. An example can be seen in values to increase significantly. COSMO-DE did forecast an Fig. 1, where the model forecast (15h) and real time environment, supportive for organized thunderstorms but the measurements are overlaid. Finally, it was compared how model failed to forecast the discrete nature of this well severe thunderstorm forecast parameters captured the thunderstorm and the deviant storm motion. Therefore it particular situation. The magnitude of those values was underestimated the final strength and longevity of this compared to observations done in North America supercell. This is an example, how internal dynamics in a (Przybylinski (1995) or Davis et al. (2004)). thunderstorm can alter the local conditions in a positive or negative way for the particular thunderstorm. III. RESULTS AND CONCLUSIONS IV. ACKNOWLEDGMENTS COSMO-DE did an outstanding job on the bow echo event, as it forecast the bow in time and space correctly. Wind The authors would like to thank the DWD for offering speed shear values in the mesoscale model were similar to MIRIAM (Mikroprozessorgesteuertes Registriersystem des real time radar measurements for example by POLDIRAD Instrumentenamtes München) and COSMO-DE data. and the same was seen in the model’s precipitation forecast. Typical features for mature bow echoes, including rear inflow notches, a sharp reflectivity gradient and an intense V. REFERENCES cold pool were all captured by POLDIRAD and local surface weather data measurements. A combination of Davis, C. and coauthors, 2004: The bow echo and MCV strong shear below 3 km and a rapidly developing cold pool experiment. Bull. Amer. Meteor. Soc., 85, 1075-1093. all caused the bow echo to acquire the strength to produce hurricane-force wind gusts and persist for hours. The Przybylinski, W., 1995: The bow echo: Observations, hailstorm on 22 August 2008 featured supercell numerical simulations, and severe weather detection characteristics like a persistently rotating updraft and a methods. Wea. Forecasting, 203-218.

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