DOCSLIB.ORG

Derecho Families

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Derecho Families P4.4 DERECHO FAMILIES Walker S. Ashley* and Thomas L. Mote Climatology Research Laboratory, Atmospheric Sciences Program, Department of Geography, University of Georgia, Athens, Georgia Mace L. Bentley Meteorology Program, Department of Geography, Northern Illinois University, DeKalb, Illinois 1. INTRODUCTION 2. METHODOLOGY Early studies by Miller (1972) and Johns (1982) observed that severe weather outbreaks are likely to 2.1 Derecho Dataset repeat on several successive days across the conterminous U.S. Johns (1982) found that 71% of all The conterminous U.S. derecho dataset utilized in U.S. northwest flow (NWF) outbreaks during 1962-77 this study was compiled through several means, were associated with a series of severe weather events including: 1) two recently completed long-term (defined by Johns as any combination of two or more climatologies by Bentley and Sparks (2003) and outbreaks that occurs with no more than two calendar Coniglio and Stensrud (2004) [See 7A.2 (this volume) days between any outbreaks in the series). Most of the for further information on these datasets]; 2) an NWF outbreak series consisted of two or three severe examination of all derecho literature to reveal any weather outbreaks, but could contain as much as eight missing derecho events not documented by the or more separate outbreaks within a series. Johns and aforementioned climatological studies; 3) the inclusion Hirt (1987) suggested that warm-season derechos are of several additional events that did not meet the Johns often associated with meteorological parameters similar and Hirt (1987) length criteria due to land constraints, to those found in NWF outbreaks. In fact, Johns and but were clearly derecho events (e.g., serial derecho Hirt (1987) discovered that derechos have the crossing Florida peninsula); and 4) documenting propensity to occur in succession; their analyses derechos from 2002 and 2003 by examining the SPC’s indicating that more than one-quarter of all 1980-1983 daily on-line severe storm reports, SPC’s severe warm season derechos qualified as NWF outbreak thunderstorm event database, Storm Data, SeverePlot, series. and available radar data. In a larger climatological study, Bentley and Sparks All derechos that were identified or compiled for this (2003) established the tendency for derechos to “train” study met a set of consistent criteria analogous to that or group over similar geographic regions. They found a proposed and utilized by Bentley and Mote (1998), tendency for summer, northern-tier U.S. derechos (a Bentley and Sparks (2003), Evans and Doswell (2001), corridor reminiscent of Johns (1982) NWF scenario) and Coniglio and Stensrud (2004; their “low-end” criteria), northeast moving, Great Plains derechos to occur in a and Coniglio et al. (2004). The unified derecho dataset, series. Although, their criteria for derecho groupings consisting of 377 events for the period 1986-2003, is was relatively liberal, with up to a 7-8 day period used to improve the record of derechos by combining between events. several sources of data into a single dataset. This study utilizes a more conservative approach to Although the derecho dataset contains 18 yr of delineate derecho groupings and a much larger dataset documented derecho events, only the 10 yr period from to reveal the characteristics of these derecho groupings. 1994-2003 is utilized for this study. The reason for this This investigation reviews 10 yr of derecho data in order restriction is due to the large jump in the number of to detail the tendency for these convective events to annual events evident after 1993 (Fig. 1). For example, replicate in coherent succession. Two or more derecho the ten-year period between 1994 and 2003 consists of events occurring within several days are labeled a over 85% of the derechos associated with families in the derecho “family” (from Bentley and Sparks 2003). dataset, while the nine-year period from 1985-1993 Corridors that are most frequented by these derecho consists of only 15% of the events. This bias is likely a families are revealed as well as the overall temporal and result of a number of human-related factors associated spatial features of derecho families in the central and with an increase in the severe wind reports contained eastern U.S. within the severe thunderstorm wind event database, including: 1) population growth and urban sprawl, 2) an increase in weather awareness by the general population, 3) improved communications (e.g., cell phones), 4) the development of spotter networks, 5) the deployment of WSR-88Ds, and 6) the implementation of the national warning verification program which has * Corresponding author address: Walker S. Ashley, resulted in increased accountability of NWS warning #204 GG Building, Dept. of Geography, Univ. of products (Schaefer et al. 2003). Hence, for the years Georgia, Athens, GA 30602; e-mail: [email protected] prior to the NWS modernization, many derecho events may be unidentified, resulting in an underestimate of the events has dissipated. Hence, the first requirement in actual number of events during this early period of the developing a derecho family classification is to develop dataset (Coniglio and Stensrud 2004). Therefore, this a temporal restriction that will limit the time interval data restriction allows for an examination of the most between subsequent storms. Initially, in order to consistent portion of the derecho database, which is a establish derecho families from the dataset, we desirable condition when examining time-series data. determined the amount of time (in hr) that occurred between the last wind report from the previous derecho and the first wind report of the next derecho. Number of Events Interestingly, the dataset reveals a strong clustering of 40 Number of Events in Families derechos around the low-end of the reoccurrence Number of Families interval distribution (Fig. 2). This supports the hypothesis that derechos have a tendency to form in coherent succession. 30 20 10 0 20 20 20 20 1986 1987 1988 198 199 199 199 199 199 199 199 199 199 199 00 01 02 03 9 0 1 2 3 4 5 6 7 8 9 Year Figure 1. The number of derechos annually for the period 1986-2003 and the number of derecho families and derecho family members for the period 1994-2003. 2.2 Derecho Family Identification Numerous mechanisms and environments can promote the formation of successive MCSs, including those producing derechos, such as: traveling baroclinic Figure 2. Two frequency histogram revealing the number of waves and their associated extratropical cyclones and hours between two sequential derecho events. The outer fronts; a persistent low-level jet (LLJ) oriented histogram is restricted to 25 hr bins while the inner histogram is perpendicular to zonal-oriented front promoting limited to 9 hr bins. A dashed line within the inner histogram reveals the maximum threshold for initial family criteria. successive MCSs (Trier and Parsons 1993); a series of minor disturbances propagating through NWF aloft We subjectively determined that any events that (Johns 1984); convectively generated propagation were within three days of each other had the possibility mechanisms such as residual outflow/cold pools (Tuttle of forming in similar troposphere environments or by the and Carbone 2004), trapped gravity waves (Carbone et same mechanism. Thus, all events less than 72 hr apart al. 2002), or mesoscale convective vortices (MCVs; were selected as initial derecho family members. This Trier et al. 2000); a series of upper-level PV anomalies approach is much more restrictive than the 7-8 day migrating atop a large-scale, stagnant ridge (Bosart et temporal restriction put forth by Bentley and Sparks al. 1998). Moreover, Stensrud (1996) found that a (2003) but consistent with the method that Johns (1982) persistent, mesoscale region of convection could have a utilized to identify NWF series – i.e., any combination of significant impact on the large-scale environment that, in two or more NWF outbreaks that occur with no more turn, can produce a positive feedback mechanism that than two calendar days between any of the outbreaks of promotes more convective systems. Although this study the series. Of the 377 derechos occurring between does not specifically classify the derecho families into 1986-2003, 225 (60%) derechos met the initial family their formative environments or mechanisms, we do use criteria. a temporal restriction and a subjective assessment of After these preliminary events were selected, 500 the large-scale environment and distance between mb and surface analyses from the Daily Weather Map systems to define the families. Series were examined for all days within each derecho Undoubtedly, the longer the interlude between two family temporal window. All events that either were successive derechos, the greater the probability that the geographically (e.g., one event in North Dakota, another environment that generated the events has undergone in Florida) or synoptically (e.g., associated with change or the mechanism that produced the series of significantly differing mid-level tropospheric patterns or 70 surface boundaries) disparate were discarded from the Number of Events derecho family dataset. Groupings of derechos that met Number of Families Number of Events in Families the initial temporal family criteria but also contained 60 embedded derecho groupings associated with differing synoptic conditions were separated in order to create consistent families for each distinguishing environment. 50 3. RESULTS 40 3.1 Temporal Frequency 30 Of the 290 events in the derecho dataset from 1994- 2003, 180 (62% of the dataset) met the family criteria 20 discussed in the previous section. The 180 events consisted of 59 families with a mean of 3.05 derechos per family. On average, there were 5.9 families and 18 10 family members annually. Most families involved only two or three derecho events; however, 14 families 0 contained four or more events.
Load more

Recommended publications
  • Squall Lines: Meteorology, Skywarn Spotting, & a Brief Look at the 18
    Squall Lines: Meteorology, Skywarn Spotting, & A Brief Look At The 18 June 2010 Derecho Gino Izzi National Weather Service, Chicago IL Outline • Meteorology 301: Squall lines – Brief review of thunderstorm basics – Squall lines – Squall line tornadoes – Mesovorticies • Storm spotting for squall lines • Brief Case Study of 18 June 2010 Event Thunderstorm Ingredients • Moisture – Gulf of Mexico most common source locally Thunderstorm Ingredients • Lifting Mechanism(s) – Fronts – Jet Streams – “other” boundaries – topography Thunderstorm Ingredients • Instability – Measure of potential for air to accelerate upward – CAPE: common variable used to quantify magnitude of instability < 1000: weak 1000-2000: moderate 2000-4000: strong 4000+: extreme Thunderstorms Thunderstorms • Moisture + Instability + Lift = Thunderstorms • What kind of thunderstorms? – Single Cell – Multicell/Squall Line – Supercells Thunderstorm Types • What determines T-storm Type? – Short/simplistic answer: CAPE vs Shear Thunderstorm Types • What determines T-storm Type? (Longer/more complex answer) – Lot we don’t know, other factors (besides CAPE/shear) include • Strength of forcing • Strength of CAP • Shear WRT to boundary • Other stuff Thunderstorm Types • Multi-cell squall lines most common type of severe thunderstorm type locally • Most common type of severe weather is damaging winds • Hail and brief tornadoes can occur with most the intense squall lines Squall Lines & Spotting Squall Line Terminology • Squall Line : a relatively narrow line of thunderstorms, often
    [Show full text]
  • A Preliminary Investigation of Derecho
    7.A.1 TROPICAL CYCLONE TORNADOES – A RESEARCH AND FORECASTING OVERVIEW. PART 1: CLIMATOLOGIES, DISTRIBUTION AND FORECAST CONCEPTS Roger Edwards Storm Prediction Center, Norman, OK 1. INTRODUCTION those aspects of the remainder of the preliminary article Tropical cyclone (TC) tornadoes represent a relatively that was not included in this conference preprint, for small subset of total tornado reports, but garner space considerations. specialized attention in applied research and operational forecasting because of their distinctive origin within the envelope of either a landfalling or remnant TC. As with 2. CLIMATOLOGIES and DISTRIBUTION PATTERNS midlatitude weather systems, the predominant vehicle for tornadogenesis in TCs appears to be the supercell, a. Individual TCs and classifications particularly with regard to significant1 events. From a framework of ingredients-based forecasting of severe TC tornado climatologies are strongly influenced by the local storms (e.g., Doswell 1987, Johns and Doswell prolificacy of reports with several exceptional events. 1992), supercells in TCs share with their midlatitude The general increase in TC tornado reports, noted as relatives the fundamental environmental elements of long ago as Hill et al. (1966), and in the occurrence of sufficient moisture, instability, lift and vertical wind “outbreaks” of 20 or more per TC (Curtis 2004) probably shear. Many of the same processes – including those is a TC-specific reflection of the recent major increase in involving baroclinicity at various scales – appear
    [Show full text]
  • A 10-Year Radar-Based Climatology of Mesoscale Convective System Archetypes and Derechos in Poland
    AUGUST 2020 S U R O W I E C K I A N D T A S Z A R E K 3471 A 10-Year Radar-Based Climatology of Mesoscale Convective System Archetypes and Derechos in Poland ARTUR SUROWIECKI Department of Climatology, University of Warsaw, and Skywarn Poland, Warsaw, Poland MATEUSZ TASZAREK Department of Meteorology and Climatology, Adam Mickiewicz University, Poznan, Poland, and National Severe Storms Laboratory, Norman, Oklahoma, and Skywarn Poland, Warsaw, Poland (Manuscript received 29 December 2019, in final form 3 May 2020) ABSTRACT In this study, a 10-yr (2008–17) radar-based mesoscale convective system (MCS) and derecho climatology for Poland is presented. This is one of the first attempts of a European country to investigate morphological and precipitation archetypes of MCSs as prior studies were mostly based on satellite data. Despite its ubiquity and significance for society, economy, agriculture, and water availability, little is known about the climatological aspects of MCSs over central Europe. Our results indicate that MCSs are not rare in Poland as an annual mean of 77 MCSs and 49 days with MCS can be depicted for Poland. Their lifetime ranges typically from 3 to 6 h, with initiation time around the afternoon hours (1200–1400 UTC) and dissipation stage in the evening (1900–2000 UTC). The most frequent morphological type of MCSs is a broken line (58% of cases), then areal/cluster (25%), and then quasi- linear convective systems (QLCS; 17%), which are usually associated with a bow echo (72% of QLCS). QLCS are the feature with the longest life cycle.
    [Show full text]
  • Template for Electronic Journal of Severe Storms Meteorology
    Lyza, A. W., A. W. Clayton, K. R. Knupp, E. Lenning, M. T. Friedlein, R. Castro, and E. S. Bentley, 2017: Analysis of mesovortex characteristics, behavior, and interactions during the second 30 June‒1 July 2014 midwestern derecho event. Electronic J. Severe Storms Meteor., 12 (2), 1–33. Analysis of Mesovortex Characteristics, Behavior, and Interactions during the Second 30 June‒1 July 2014 Midwestern Derecho Event ANTHONY W. LYZA, ADAM W. CLAYTON, AND KEVIN R. KNUPP Department of Atmospheric Science, Severe Weather Institute—Radar and Lightning Laboratories University of Alabama in Huntsville, Huntsville, Alabama ERIC LENNING, MATTHEW T. FRIEDLEIN, AND RICHARD CASTRO NOAA/National Weather Service, Romeoville, Illinois EVAN S. BENTLEY NOAA/National Weather Service, Portland, Oregon (Submitted 19 February 2017; in final form 25 August 2017) ABSTRACT A pair of intense, derecho-producing quasi-linear convective systems (QLCSs) impacted northern Illinois and northern Indiana during the evening hours of 30 June through the predawn hours of 1 July 2014. The second QLCS trailed the first one by only 250 km and approximately 3 h, yet produced 29 confirmed tornadoes and numerous areas of nontornadic wind damage estimated to be caused by 30‒40 m s‒1 flow. Much of the damage from the second QLCS was associated with a series of 38 mesovortices, with up to 15 mesovortices ongoing simultaneously. Many complex behaviors were documented in the mesovortices, including: a binary (Fujiwhara) interaction, the splitting of a large mesovortex in two followed by prolific tornado production, cyclic mesovortexgenesis in the remains of a large mesovortex, and a satellite interaction of three small mesovortices around a larger parent mesovortex.
    [Show full text]
  • ESSENTIALS of METEOROLOGY (7Th Ed.) GLOSSARY
    ESSENTIALS OF METEOROLOGY (7th ed.) GLOSSARY Chapter 1 Aerosols Tiny suspended solid particles (dust, smoke, etc.) or liquid droplets that enter the atmosphere from either natural or human (anthropogenic) sources, such as the burning of fossil fuels. Sulfur-containing fossil fuels, such as coal, produce sulfate aerosols. Air density The ratio of the mass of a substance to the volume occupied by it. Air density is usually expressed as g/cm3 or kg/m3. Also See Density. Air pressure The pressure exerted by the mass of air above a given point, usually expressed in millibars (mb), inches of (atmospheric mercury (Hg) or in hectopascals (hPa). pressure) Atmosphere The envelope of gases that surround a planet and are held to it by the planet's gravitational attraction. The earth's atmosphere is mainly nitrogen and oxygen. Carbon dioxide (CO2) A colorless, odorless gas whose concentration is about 0.039 percent (390 ppm) in a volume of air near sea level. It is a selective absorber of infrared radiation and, consequently, it is important in the earth's atmospheric greenhouse effect. Solid CO2 is called dry ice. Climate The accumulation of daily and seasonal weather events over a long period of time. Front The transition zone between two distinct air masses. Hurricane A tropical cyclone having winds in excess of 64 knots (74 mi/hr). Ionosphere An electrified region of the upper atmosphere where fairly large concentrations of ions and free electrons exist. Lapse rate The rate at which an atmospheric variable (usually temperature) decreases with height. (See Environmental lapse rate.) Mesosphere The atmospheric layer between the stratosphere and the thermosphere.
    [Show full text]
  • A Preliminary Investigation of Derecho-Producing Mcss In
    P 3.1 TROPICAL CYCLONE TORNADO RECORDS FOR THE MODERNIZED NWS ERA Roger Edwards1 Storm Prediction Center, Norman, OK 1. INTRODUCTION and BACKGROUND since 1954 was attributable to the weakest (F0) bin of damage rating (Fig. 1). This is the very class of Tornadoes from tropical cyclones (hereafter TCs) tornado that is most common in TC records, and most pose a specialized forecast challenge at time scales difficult to detect in the damage above that from the ranging from days for outlooks to minutes for concurrent or subsequent passage of similarly warnings (Spratt et al. 1997, Edwards 1998, destructive, ambient TC winds. As such, it is possible Schneider and Sharp 2007, Edwards 2008). The (but not quantifiable) that many TC tornadoes have fundamental conceptual and physical tenets of gone unrecorded even in the modern NWS era, due midlatitude supercell prediction, in an ingredients- to their generally ephemeral nature, logistical based framework (e.g., Doswell 1987, Johns and difficulties of visual confirmation, presence of swaths Doswell 1992), fully apply to TC supercells; however, of sparsely populated near-coastal areas (i.e., systematic differences in the relative magnitudes of marshes, swamps and dense forests), and the moisture, instability, lift and shear in TCs (e.g., presence of damage inducers of potentially equal or McCaul 1991) contribute strongly to that challenge. greater impact within the TC envelope. Further, there is a growing realization that some TC tornadoes are not necessarily supercellular in origin (Edwards et al. 2010, this volume). Several major TC tornado climatologies have been published since the 1960s (e.g., Pearson and Sadowski 1965, Hill et al.
    [Show full text]
  • Rapid Assessment of Tree Damage Resulting from a 2020 Windstorm in Iowa, USA
    Article Rapid Assessment of Tree Damage Resulting from a 2020 Windstorm in Iowa, USA Thomas C. Goff 1,*, Mark D. Nelson 1, Greg C. Liknes 1, Tivon E. Feeley 2 , Scott A. Pugh 1 and Randall S. Morin 1 1 Northern Research Station, USDA Forest Service, Madison, WI 53726, USA; [email protected] (M.D.N.); [email protected] (G.C.L.); [email protected] (S.A.P.); [email protected] (R.S.M.) 2 Iowa Department of Natural Resources, Des Moines, IA 50319, USA; [email protected] * Correspondence: [email protected] Abstract: A need to quantify the impact of a particular wind disturbance on forest resources may require rapid yet reliable estimates of damage. We present an approach for combining pre-disturbance forest inventory data with post-disturbance aerial survey data to produce design-based estimates of affected forest area and number and volume of trees damaged or killed. The approach borrows strength from an indirect estimator to adjust estimates from a direct estimator when post-disturbance remeasurement data are unavailable. We demonstrate this approach with an example application from a recent windstorm, known as the 2020 Midwest Derecho, which struck Iowa, USA, and adjacent states on 10–11 August 2020, delivering catastrophic damage to structures, crops, and trees. We 3 estimate that 2.67 million trees and 1.67 million m of sound bole volume were damaged or killed on 23 thousand ha of Iowa forest land affected by the 2020 derecho. Damage rates for volume Citation: Goff, T.C.; Nelson, M.D.; were slightly higher than for number of trees, and damage on live trees due to stem breakage was Liknes, G.C.; Feeley, T.E.; Pugh, S.A.; more prevalent than branch breakage, both likely due to higher damage probability in the dominant Morin, R.S.
    [Show full text]
  • 4 Derecho: Fast State Machine Replication for Cloud Services
    4 Derecho: Fast State Machine Replication for Cloud Services SAGAR JHA, Cornell University, USA JONATHAN BEHRENS, Cornell University, USA and MIT, USA THEO GKOUNTOUVAS, MATTHEW MILANO, WEIJIA SONG, EDWARD TREMEL, ROBBERT VAN RENESSE, SYDNEY ZINK, and KENNETH P. BIRMAN, Cornell University, USA Cloud computing services often replicate data and may require ways to coordinate distributed actions. Here we present Derecho, a library for such tasks. The API provides interfaces for structuring applications into patterns of subgroups and shards, supports state machine replication within them, and includes mechanisms that assist in restart after failures. Running over 100Gbps RDMA, Derecho can send millions of events per second in each subgroup or shard and throughput peaks at 16GB/s, substantially outperforming prior solu- tions. Configured to run purely on TCP, Derecho is still substantially faster than comparable widely used, highly-tuned, standard tools. The key insight is that on modern hardware (including non-RDMA networks), data-intensive protocols should be built from non-blocking data-flow components. CCS Concepts: • Computer systems organization → Dependable and fault tolerant systems and networks; • Software and its engineering → Cloud computing; Additional Key Words and Phrases: Cloud computing, RDMA, non-volatile memory, replication, consistency ACM Reference format: Sagar Jha, Jonathan Behrens, Theo Gkountouvas, Matthew Milano, Weijia Song, Edward Tremel, Robbert van Renesse, Sydney Zink, and Kenneth P. Birman. 2019. Derecho: Fast State Machine Replication for Cloud Services. ACM Trans. Comput. Syst. 36, 2, Article 4 (March 2019), 49 pages. https://doi.org/10.1145/3302258 1 INTRODUCTION There is a pervasive need for cloud-hosted services that guarantee rapid response based on the most up-to-date information, scale well, and support high event rates.
    [Show full text]
  • The Historic Derecho of June 29, 2012
    Service Assessment The Historic Derecho of June 29, 2012 U.S. DEPARTMENT OF COMMERCE National Oceanic and Atmospheric Administration National Weather Service Silver Spring, Maryland Cover Photograph: Visible satellite image at 5 p.m. Eastern Daylight Time (EDT) June 29, 2012, as the derecho moved across Ohio. National Lightning Data Network (NLDN) Cloud to ground (CG) lightning strikes for the 1-hour period, 4-5 p.m. EDT, are plotted in red. Surface observations are plotted in green. Smaller insets show radar reflectivity images of the derecho during the afternoon and evening. ii Service Assessment The Historic Derecho of June 29, 2012 January 2013 National Weather Service Laura K. Furgione Acting Assistant Administrator for Weather Services iii Preface On June 29, 2012, a derecho of historic proportions struck the Ohio Valley and Mid-Atlantic states. The derecho traveled for 700 miles, impacting 10 states and Washington, D.C. The hardest hit states were Ohio, West Virginia, Virginia, and Maryland, as well as Washington, D.C. The winds generated by this system were intense, with several measured gusts exceeding 80 mph. Unfortunately, 13 people were killed by the extreme winds, mainly by falling trees. An estimated 4 million customers lost power for up to a week. The region impacted by the derecho was also in the midst of a heat wave. The heat, coupled with the loss of power, led to a life-threatening situation. Heat claimed 34 lives in areas without power following the derecho. Due to the significance of this event, the National Oceanic and Atmospheric Administration’s National Weather Service formed a Service Assessment Team to evaluate the National Weather Service’s performance before and during the event.
    [Show full text]
  • City of Minneapolis Office of Emergency Management
    CITY OF MINNEAPOLIS OFFICE OF EMERGENCY MANAGEMENT Straight Line Wind Fact Sheet AM I AT RISK? Since most thunderstorms produce some straight–line The term “straight–line” wind is used to differentiate the winds as a result of outflow generated by the thunderstorm damage they cause from tornado damage. Strong, downdraft, anyone living in thunderstorm–prone areas is at damaging winds can come from a number of different risk. Damage from severe thunderstorm winds account for thunderstorm processes. Most thunderstorm winds that half of all severe reports in the lower 48 states and is more cause damage at the ground are a result of outflow common than damage from tornadoes. Wind speeds can generated by a thunderstorm downdraft. Damaging winds reach up to 100 mph and can produce a damage path are classified as those exceeding 50–60 mph. A severe extending for hundreds of miles. thunderstorm is capable of producing winds with speeds faster than 100 mph, even without a tornado. People living in mobile homes are especially at risk for injury and death. Even anchored mobile homes can be A storm that is capable of producing consistent straight– seriously damaged when winds gust over 80 mph. line winds of 58 mph or more and covers an area of more People who are outdoors are most at risk to straight line than 240 miles is known as a “derecho”. A derecho is a wind. Campers or hikers in forested areas are vulnerable to widespread, long–lived wind storm that is associated with being injured or killed by falling trees, and people on bodies a band of rapidly moving showers or thunderstorms.
    [Show full text]
  • The 1 June 2004 North Texas-Louisiana Derecho
    The 1 June 2004 North Texas Derecho: A Case Study Abstract A case study of the 1 June 2004 storms that produced damaging winds across north Texas and Louisiana is presented. The synoptic and mesoscale environment is analyzed with emphasis on operational forecast parameters. Northwesterly flow aloft and strong instability produced a favorable environment for a linear mesoscale convective system (MCS). Storm evolution is analyzed from initiation through MCS organization using archived data from the Weather Event Simulator (WES). Although surface boundaries played an important role in storm initiation, the storms moved away from those boundaries and were not dependent on them to sustain convection. Early in the episode, right and left supercell splits were observed. Two supercells in close proximity to each other developed intense outflow winds and then merged with new convection to form a forward- propagating MCS. In this case, individual supercells played an important role in the event, producing some of the most damaging winds. The intense winds produced damage to trees, buildings, and power lines over a wide swath more than 400 km long and 100 km wide. 1. Introduction Forecasting damaging straight line wind events is important because these storms account for a significant amount of property damage and casualties. A recent study that compared derechos to hurricanes and tornadoes during the period of 1986- 2003 concluded that derechos can be similar to most United States tornadoes and hurricanes in terms of their threat to life and property (Ashley and Mote 2005). One such storm event affected the Dallas- Ft. Worth Metroplex and the region to its east during the evening and overnight hours of 1- 2 June 2004.
    [Show full text]
  • A Preliminary Investigation of Derecho
    P 8.2 ARCHETYPES FOR SURFACE BAROCLINIC BOUNDARIES INFLUENCING TROPICAL CYCLONE TORNADO OCCURRENCE Roger Edwards1 Storm Prediction Center, Norman, OK Albert E. Pietrycha National Weather Service Forecast Office, Goodland, KS 1. INTRODUCTION and BACKGROUND considerations (i.e., the radar based studies by Spratt et al. 1997 and Rao et al. 2004). Also in common with The distribution of tornadoes within landfalling tropical midlatitude systems, those ingredients may be focused cyclones (TCs) in the United States has been in the vicinity of thermodynamic inhomogeneities and documented and examined since World War II, associated with tornado occurrence, whether at the beginning with coarse estimations (e.g., Tannehill 1950, surface (e.g., Rao et al. 2000) or aloft (Curtis 2004). Malkin and Galway 1953, Sadowski 1962), and continuing with more refined climatological plots as Our aim is to blend those two fundamental concepts to tornadoes have become more thoroughly reported (e.g., benefit short-term, operational prediction, as applied to Hill et al. 1966, Novlan and Gray 1974, Gentry 1983). analyses of surface features that may influence Despite minor inconsistencies, these efforts environmental ingredients suitable for tornadic progressively reinforced the notion that tornadoes tend supercells. We illustrate four categories of association to develop north through east of center, with the majority (Table 1) between baroclinic boundaries and TC outside the radius of gale winds. tornado distribution, using idealized conceptual models based on actual mesoanalytic examples from recent As TC tornado climatologies became more robust, storms. TC-embedded frontal boundaries may originate forecasters and researchers investigated environments a priori, as in orographically influenced frontal zones associated with the outer-northeastern quadrants which, and synoptic fronts, or in situ, as with areas of diurnal, in turn, further concentrated the understanding of the differential diabatic heating.
    [Show full text]