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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. Motivation. - PowerPoint PPT Presentation
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A Study of Cool Season Tornadoes in the Southeast United States
Alicia C. Wasula and Lance F. BosartUniversity at Albany/SUNY
andRussell Schneider, Steven J. Weiss, and Robert
H. JohnsStorm Prediction Center
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
Number >=F2 Tornadoes
Number Cool Season >=F2 Tornadoes
FL 228 115
CO 396 210
AP 976 460
MR
1071 560
OZ 250 142
Cool Season = November-March
Percent Tornadoes (>=F2) byMonth
Percent Tornadoes (>=F2)by Hour (UTC)
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)
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 (%)
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)
Blue = Wind > 25.7 m s-1
Green = Hail > 1.91 cm
Red = Tornado
SEVERE WEATHER REPORTS: 22-23 February 1998
7 Tornadoes3 F342 Fatalities260 Injuries
22 February 1998 0000 UTC AVN Analysis
SFC
850 hPa
500 hPa
200 hPa
22 February 1998 1200 UTC AVN Analysis
SFC
850 hPa
500 hPa
200 hPa
23 February 1998 0000 UTC AVN Analysis
SFC
850 hPa
500 hPa
200 hPa
CAPE = 2891 J/kgLI = -9 CLCL = 962 hPa
Tampa Bay (TBW) Sounding and Hodograph 23 February 1998 0000 UTC
U (m s-1)
V (m
s-1)
22/1815 UTCIR Satellite
22/2115 UTCIR Satellite
22/2345 UTCIR Satellite
23/0015 UTCIR Satellite
23/0015 UTC22/2255 UTC
23/0100 UTCBREF MosaicSurface Temp. (°C) and contours
23/0315 UTC23/0145 UTC
23/0200 UTCBREF MosaicSurface Temp. (°C) and contours
23/0530 UTC
23/0300 UTCBREF MosaicSurface Temp. (°C) and contours
23/0400 UTCBREF MosaicSurface Temp. (°C) and contours
23/0500 UTCBREF MosaicSurface Temp. (°C) and contours
23/0600 UTCBREF MosaicSurface Temp. (°C) and contours
Number of Lightning Strikes80-88W (Band 25-32N)
22/18Z-23/9Z
Longitude (Deg. West)
Tim
e (U
TC)
>100>200>300>400>500>600
88 87 86 85 84 83 82 81 80
22/1800
22/190022/2000
23/090023/080023/070023/060023/050023/040023/0300
23/0200
23/000022/230022/220022/2100
23/0100
SST’ > 0 SST’<0 LAND
Surface Frontogenesis (°C 100 km-1 3 h-1)23/0000 UTC
23/0600UTC
23/0200UTC
23/0400UTC
Surface TrajectoriesEnding 23/0400 UTC
End point north of boundaryEnd point south of boundary
Surface Vorticity (x 10-5 s-1)23/0000 UTC
23/0600UTC
23/0200UTC
23/0400UTC
• 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
