SWODY1
SPC AC 251623
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1123 AM CDT WED MAY 25 2011
VALID 251630Z - 261200Z
...THERE IS A HIGH RISK OF SVR TSTMS THIS AFTERNOON INTO EARLY
TONIGHT OVER PARTS OF NORTHEAST AR...WEST TN...SOUTHEAST
MO...SOUTHERN IL...WESTERN AND CENTRAL KY...AND SOUTHERN IND...
...THERE IS A MDT RISK OF SVR TSTMS FROM SOUTHERN AR AND NORTHERN MS
ACROSS MUCH OF THE MID MS/OH AND TN RIVER VALLEYS...
...THERE IS A SLGT RISK OF SVR TSTMS FROM NORTHERN LA INTO THE
EASTERN GREAT LAKES...
...MAJOR TORNADO OUTBREAK IS FORECAST LATER TODAY AND TONIGHT OVER
PORTIONS OF THE MID MS AND LOWER OH VALLEYS...
A STRONG UPPER LOW OVER KS WILL MOVE SLOWLY EASTWARD TODAY...WHILE A
SHORTWAVE TROUGH ROTATES AROUND THE SOUTHERN PERIPHERY OF THE LOW
INTO THE MID MS AND LOWER OH VALLEYS. A LARGE BAND OF 70+ KNOT
WESTERLY MID LEVEL WINDS STRETCH FROM OK/TX INTO IL/KY/TN THIS
MORNING...ACROSS A LARGE/MOIST WARM SECTOR. AN EXPANSIVE AREA OF
MID/UPPER 60S DEWPOINTS EXTEND FROM THE COLD FRONT OVER WRN MO/AR
EASTWARD TO EASTERN KY AND NORTHWARD INTO NORTHERN IND. THE RESULT
WILL BE A VERY DANGEROUS RISK OF WIDESPREAD SEVERE THUNDERSTORMS
LATER THIS AFTERNOON AND EVENING...INCLUDING LONG-DURATION
STRONG/VIOLENT TORNADOES.
MORNING RAOBS AND FORECAST SOUNDINGS SUGGEST THAT WIDESPREAD MOIST
AND VERY UNSTABLE CONDITIONS WILL BE PRESENT ACROSS THE WARM SECTOR
TODAY. BROKEN CLOUDS WILL YIELD AFTERNOON MLCAPE VALUES OF
2500-3500 J/KG OVER A LARGE AREA...ALONG WITH A RELATIVELY WEAK CAP.
THIS WILL RESULT IN THE POTENTIAL FOR MULTIPLE ROUNDS OF SEVERE
THUNDERSTORMS ACROSS THE AREA...BOTH IN THE WARM SECTOR...AND ALONG
THE SURFACE COLD FRONT AS IT SWEEPS EASTWARD LATER TODAY.
TCU AND THUNDERSTORMS HAVE BEGUN TO DEVELOP AHEAD OF THE UPPER LOW
AND NEAR THE COLD FRONT OVER WESTERN MO/AR. THE 15Z SGF RAOB SHOWS
FAVORABLE VERTICAL SHEAR PROFILES FOR SUPERCELL THUNDERSTORMS
CAPABLE OF VERY LARGE HAIL AND TORNADOES. THESE STORMS SHOULD
INTENSIFY THROUGH THE DAY WITH AN INCREASING RISK OF STRONG/VIOLENT
TORNADOES. ONCE THESE STORMS BECOME ESTABLISHED...THEY MAY PERSIST
THROUGH MUCH OF THE FORECAST PERIOD AND SURGE EASTWARD ACROSS THE
MDT/HIGH RISK AREAS.
FARTHER EAST...SEVERAL MODEL SOLUTIONS INDICATE THE DEVELOPMENT OF
CONVECTION IN THE WARM SECTOR OVER PORTIONS OF NORTHEAST
AR/SOUTHEAST MO/SOUTHERN IL/WESTERN KY...SPREADING INTO WEST TN AND
SOUTHERN IND. 0-3KM SRH VALUES OF 250-400 M2/S2 COUPLED WITH LONG
HODOGRAPHS AND HIGH INSTABILITY SUGGEST THESE STORMS WOULD LIKELY BE
DISCRETE SUPERCELLS WITH AN INCREASING RISK OF MULTIPLE
STRONG/VIOLENT TORNADOES AND VERY LARGE HAIL.
DURING THE EVENING...MULTIPLE LINES/CLUSTERS OF INTENSE/SUPERCELL
STORMS AND BOWS MAY BE TRACKING RAPIDLY EAST-NORTHEASTWARD ACROSS
THE MDT/HIGH RISK AREAS. GIVEN THE LARGE AREA POTENTIALLY AFFECTED
BY SEVERE STORMS TODAY...THE STRENGTH OF THE LOW AND DEEP LAYER
SHEAR...AND THE STRONG INSTABILITY...THE POTENTIAL IS INCREASING FOR
A MAJOR TORNADO OUTBREAK. WIDESPREAD WIND DAMAGE AND LARGE HAIL ARE
ALSO A PROMINENT CONCERN THROUGH THE EVENING HOURS.
BY MID TO LATE EVENING...THUNDERSTORMS ARE LIKELY TO DEVELOP
SOUTHWARD ALONG THE COLD FRONT INTO SOUTHERN AR/NORTHERN LA. THIS
ACTIVITY WILL BE NEAR THE NOSE OF A STRONG WESTERLY MID LEVEL
JET...AND MAY POSE A RISK OF SIGNIFICANT SEVERE WEATHER AS WELL.
UNCERTAINTY EXISTS REGARDING THE COVERAGE OF STORMS IN THIS
AREA...BUT NONETHELESS HAVE EXTENDED THE MDT RISK SLIGHTLY FARTHER
SOUTH TO HIGHLIGHT THIS THREAT.
..HART/GRAMS.. 05/25/2011
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