MESOSCALE CONVECTIVE SYSTEMS PRODUCING SEVERE WEATHER IN CATALONIA Rigo, T. (1), M.C. Llasat (2), C. Farnell (1), A. del Moral (2) (1) Servei Meteorologic de Catalunya (2) Dept. Applied Physics- Group of Meteorology, University of Barcelona Motivation Starting points MCS are associated with most of floods in Catalonia (Rigo and Llasat, 2007) Severe weather phenomena is common and produce large damages in Catalonia (Farnell et al., 2017) Then We want to answer: are MCS and severe weather associated in Catalonia? 2 Presentation: definitions and area of study Mesoscale Convective Systems: thunderstorm regions which may be round or linear in shape, on the order of 100 kilometres or more across an axis. Houze et al. (1990) regions with Z>12 dBZ & Area>10,000 km2 Standing for 3 hours or more Stratiform/convective rainfall types discriminated by 35 dBZ threshold 3 Presentation: definitions and area of study Lightning Jump (LJ): sudden increase of total lightning activity in thunderstorms, associated with strong updrafts Continuity in time (>14 min) and in X=current time (TL avg) Pi=previous time (TL avg) space X-P6 > 2 * σ Two levels of warnings: (1) for small hail, heavy rainfall and moderate winds, (2) for severe weather. (Multiplicity of flashes) 4 Presentation: definitions and area of study Severe weather: phenomena associated with thunderstorms, in any of these forms: large hail (>2 cm), strong winds and downbursts (> 25 m/s), and tornadoes/waterspouts The SMC has developed a data base of severe weather for the period 2006-now 1,041 registers for the period of analysis (2012-2016): 147 observations of hail, 19 of tornado/waterspout, and 875 of strong winds/downburst Some cases need to be re-analysed, because some phenomena have not been included 5 Presentation: definitions and area of study The area of study Radar for MCS identification LLS for the triggering of LJ warnings Important relationship between LJ warnings and severe weather occurrence 6 Motivation Then We want to answer to: are MCS and severe weather associated in Catalonia? How: Comparing the DDBB of MCS and LJ warnings (Severe Weather) 7 The automatic identification of MCS Results presented in the 342 MCS were identified for the “Spring” “Autumn” period of study (2012-2016) CO-WA (March/April), ~26.5% of cases WA-CO (September-November), ~27.4% of cases 8 The automatic identification of MCS Lightning activity in MCS rate TL/QPE: 57.7 flashes/mm (CO-WA) and 786.6 flashes/mm (WA-CO) Could be a link between this largest lightning activity and severe weather? 9 DDBB of LJ warnings. Relationship with severe weather Analysis of the period 2012-2016 (same that for MCS) We have analysed the warnings and the MCS at the time of the LJW (left) and for the whole life cycle (right) 10 DDBB of LJ warnings. Relationship with severe weather Analysis of the period 2012-2016 (same that for MCS) MCS area vs LJW (both levels) MCS conv. area vs LJW (level 2) 11 Results Analysis of the period 2012-2016 (same that for MCS) 342 MCS analyzed during the period of study Only a 30% of them have at least on LJ warning associated directly or indirectly (other convective structures) Only a 21% of the MCS have associated a LJ warning of level 2 740 LJWs coinciding with MCS (some systems have more than 4 warnings): - 46.75% out of the MCS (associated with other rainfall structures) - 32.97% in the stratiform region - Only 20.27% in the convective area Only a 15% of the warnings in MCS were related with severity (LJW2) 12 Results Monthly and hourly analysis (MCS with LJ and total) Link between time and diurnal cycle of convection Occurrence between March and November Maximum JJA 13 Results Comparing MCS with and without LJW More intense Higher electrical activity Similar duration 14 Conclusions Some relevant points about MCS related to severe weather The number of MCS producing severe weather is reduced (~21%) and concentrated in the months between April and November However, the number of systems producing small hail or heavy rainfall is larger (30%) A fourth of the warnings in MCS are produced in the stratiform region, while a mid occur in convection out of the system The MCS producing severe weather have a similar duration than others, but have higher values of reflectivity and larger lightning activity 15 Conclusions Answer to the initial question Even severe weather is possible in MCS, the relationship between both is weak Why? Because severe weather is associated with very strong updrafts, more common in other types of convective modes (squall lines or supercells) 16 Thanks Annex XDDE geographic map Multiplicity in CG & IC flashes LMA XDDE Only 2D, instead of 3D such LMA (-) Less sources then for LMA… (1/25) (-) Better coverage that LMA (+) But many more tan operative LLS with LF only (10/3) (+) 18 DDBB of LJ warnings. Relationship with severe weather MCS related with Severe Weather • We have assumed relationship level 2 (LJ) with severe weather • The period with cases is reduced to April to October • The maximum is focused in July and August 19 .