1. A Study of Cool Season Tornadoes in the Southeast United States Alicia C. Wasula and Lance F. Bosart University at Albany/SUNY and Russell Schneider, Steven J. Weiss, and Robert H. Johns Storm Prediction Center

2. Motivation Understand physical mechanisms behind cool season (November – March) tornado occurrence in the Southeast U.S. Understand role of mesoscale features in modifying large-scale environment to enhance or inhibit tornado development

3. Number >=F2 Tornadoes Number Cool Season >=F2 Tornadoes FL228115 CO396210 AP976460 MRMR 1071560 OZ250142 Cool Season = November-March

5. Percent Tornadoes (>=F2) by Month Percent Tornadoes (>=F2) by Hour (UTC)

6. COMPOSITE TORNADO EVENT 0000-0600 UTC (n=393, Tornado point = 32 N, 90 W) 500 hPa heights (solid, dam), vorticity (dashed, x 10 -5 s -1 ), vort. advection (shaded, x 10 -10 s -2 ) 200 hPa heights (solid, dam), isotachs (shaded, m s -1 )

7. COMPOSITE TORNADO EVENT 0000-0600 UTC (n=393, Tornado point = 32 N, 90 W) 850 hPa heights (solid, m), temperature (dashed, °C), temp. advection (shaded, x 10 -5 °C s -1 ) 1000 hPa heights (solid, m), 1000-500 hPa thck (dashed, dam), 700 hPa relative humidity (%)

8. 700 hPa heights (solid, m), vertical motion (dashed and shaded, x 10 -3 hPa s -1 ), 850-500 hPa lapse rate (dashed°C), 850 hPa  e (shaded, K), 850 hPa winds COMPOSITE TORNADO EVENT 0000-0600 UTC (n=393, Tornado point = 32 N, 90 W)

9. Blue = Wind > 25.7 m s -1 Green = Hail > 1.91 cm Red = Tornado SEVERE WEATHER REPORTS: 22-23 February 1998 7 Tornadoes 3 F3 42 Fatalities 260 Injuries

10. 22 February 1998 0000 UTC AVN Analysis SFC 850 hPa 500 hPa 200 hPa

11. 22 February 1998 1200 UTC AVN Analysis SFC 850 hPa 500 hPa 200 hPa

12. 23 February 1998 0000 UTC AVN Analysis SFC 850 hPa 500 hPa 200 hPa

13. CAPE = 2891 J/kg LI = -9 C LCL = 962 hPa Tampa Bay (TBW) Sounding and Hodograph 23 February 1998 0000 UTC U (m s -1 ) V (m s -1 )

15. 22/1815 UTC IR Satellite

16. 22/2115 UTC IR Satellite 22/2345 UTC IR Satellite 23/0015 UTC IR Satellite

17. 23/0015 UTC 22/2255 UTC 23/0100 UTC BREF Mosaic Surface Temp. (°C) and contours

18. 23/0315 UTC 23/0145 UTC 23/0200 UTC BREF Mosaic Surface Temp. (°C) and contours

19. 23/0530 UTC 23/0300 UTC BREF Mosaic Surface Temp. (°C) and contours

20. 23/0400 UTC BREF Mosaic Surface Temp. (°C) and contours

21. 23/0500 UTC BREF Mosaic Surface Temp. (°C) and contours

22. 23/0600 UTC BREF Mosaic Surface Temp. (°C) and contours

23. SST’ > 0 SST’<0 LAND

24. Surface Frontogenesis (°C 100 km -1 3 h -1 ) 23/ 0000 UTC 23/ 0600 UTC 23/ 0200 UTC 23/ 0400 UTC

25. Surface Trajectories Ending 23/0400 UTC End point north of boundary End point south of boundary

26. Surface Vorticity (x 10 -5 s -1 ) 23/ 0000 UTC 23/ 0600 UTC 23/ 0200 UTC 23/ 0400 UTC

27. Case study fits with composite results on synoptic scale Convection reorganized into line of tornadic supercells after landfall Intensity of squall line related to Gulf SST anomalies Strong frontogenesis maintained east-west baroclinic zone and enhance upward motion in warm air across central Florida Baroclinic zone maintained strength as surface air traversed over anomalously warm (cold) SST anomalies to south (north) Increase in ambient surface absolute vorticity on FL peninsula is associated with evolution of line into supercells Conclusions