SWODY2
SPC AC 211724
DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1224 PM CDT SAT MAY 21 2011
VALID 221200Z - 231200Z
...THERE IS A SLGT RISK OF SVR TSTMS OVER A BROAD AREA FROM THE SRN
PLAINS THROUGH THE OH...TN AND MID/UPPER MS VALLEYS...
...SYNOPSIS...
A BROAD UPPER TROUGH WILL BE SITUATED OVER THE CENTRAL STATES AND MS
VALLEY ON SUNDAY...WITH VERTICALLY STACKED LOW OVER MN DURING THE
AFTERNOON. A WEAK COLD FRONT WILL EXTEND FROM THE SURFACE LOW SWD
INTO NWRN MO/S CENTRAL KS. A SURFACE TROUGH/DRYLINE SHOULD NOT MIX
AS FAR EAST ON SUNDAY AS TODAY... DUE TO SHORTWAVE TROUGH MOVING
INTO SWRN U.S. DRYLINE EXPECTED TO BE NEAR A ICT-FSI-ABI LINE AT
LATE AFTERNOON. AN UNUSUALLY LARGE SLIGHT RISK AREA IS INCLUDED ON
THE OUTLOOK FOR SUNDAY GIVEN AT LEAST WIDESPREAD LARGE SCALE FORCING
ASSOCIATED WITH UPPER TROUGH AND PRESENCE OF A LARGE RESERVOIR OF
WARM AND VERY UNSTABLE AIR MASS EAST OF THE COLD FRONT/DRYLINE.
...TX/OK/SERN KS/SRN MO/AR/NWRN LA..
DIURNAL HEATING AND THE COMBINATION OF STEEP MID LEVEL LAPSE RATES
AND LOWER 70 SURFACE DEWPOINTS WILL RESULT IN AN EXTREMELY UNSTABLE
AIR MASS...WITH MLCAPES IN EXCESS OF 4000 J/KG. WHILE STRONG FORCING
IS NOT FORESEEN...THE PRESENCE OF WEAK TROUGHING ALOFT AND
CONVERGENCE NEAR DRYLINE/LEFTOVER OUTFLOW BOUNDARIES SHOULD BE
SUFFICIENT FOR AT LEAST ISOLATED STORMS FORMING DURING THE
AFTERNOON/EVENING HOURS. GIVEN THE EXTREME INSTABILITY AND DEEP
LAYER SHEAR AROUND 40 KT...STORMS THAT DEVELOP WILL QUICKLY EVOLVE
INTO SUPERCELLS. VERY LARGE HAIL IS EXPECTED TO BE THE PRIMARY
THREAT...SO A SIGNIFICANT AREA HAS BEEN ADDED TO THE PROBABILITIES.
ALSO...LOW LEVEL WINDS ARE FORECAST TO BACK LATER IN THE DAY...IN
RESPONSE TO SWRN U.S. TROUGH...WITH A TORNADO OR TWO POSSIBLE. IF IT
BECOMES APPARENT THAT GREATER STORM COVERAGE IS ANTICIPATED THAN
CURRENTLY THOUGHT...PORTIONS OF AREA COULD BE UPGRADED TO A MODERATE
RISK ON THE DAY 1 OUTLOOK.
AN MCS OR TWO LIKELY WILL EVOLVE FROM THESE STORMS SUNDAY EVENING
AND TRACK EWD INTO MO/AR/ERN TX/NWRN LA WITH A GREATER POTENTIAL FOR
DAMAGING WINDS.
...ERN IA/IL/WI AND UPPER MI...
EXPECT MORNING CLOUDS AND OVERNIGHT CONVECTION SHOULD DECREASE SOME
DURING THE DAY AND ALLOW AN AXIS OF STRONGER DESTABILIZATION TO
OCCUR AHEAD OF APPROACHING LOW/COLD FRONT. BOTH NAM/GFS 12Z RUNS ARE
CONSISTENT WITH 60 KT MID LEVEL SPEED MAX...ON SERN SIDE OF
SYSTEM...SHIFTING NEWD FROM SWRN IA INTO SWRN WI. ALTHOUGH HARD TO
PREDICT WHERE THE STRONGER HEATING/INSTABILITY WILL BE
LOCATED...FORCING WITH THIS SPEED MAX INDICATES SEVERE STORMS ARE
LIKELY TO DEVELOP WHERE THE THERMODYNAMIC ENVIRONMENT IS MOST
FAVORABLE. DEEP LAYER SHEAR SHOULD SUPPORT SUPERCELLS WITH HAIL AND
WIND DAMAGE. ALSO...STRENGTHENING AND VEERING LOW/MID LEVEL WINDS
ARE EXPECTED TO YIELD FAVORABLE HODOGRAPHS FOR TORNADOES. DEPENDING
ON THE INSTABILITY...THE DYNAMICAL FORCING WILL BE SUPPORTIVE OF
MAINLY A DAMAGING WIND/HAIL THREAT SPREADING EWD INTO THE LOWER MI
OVERNIGHT.
...LWR OH/TENNESSEE VALLEYS...
SWLY FLOW ALOFT AND WEAK EMBEDDED IMPULSES INDICATE THE SEVERE
EVOLUTION IN THIS REGION IS UNCERTAIN...ESPECIALLY SINCE OVERNIGHT
CONVECTION WILL STABILIZE SOME AREAS AND LEAVE BEHIND POTENTIAL
STORM-DEVELOPING OUTFLOW BOUNDARIES. ALSO...ANY REMAINING CLUSTERS
OF STORMS ONGOING DURING THE MORNING MAY REINTENSIFY LATER IN THE
DAY. IN ANY REGARD...WHERE AIR MASS WARMING OCCURS...SHEAR PLUS
MODERATE TO STRONG INSTABILITY WILL SUPPORT MULTICELL CLUSTERS...AS
WELL AS SOME SUPERCELL STRUCTURES. GIVEN DEEP SWLY FLOW ABOVE THE
BOUNDARY LAYER... UPSCALE GROWTH INTO A FEW ORGANIZED LINEAR MCS/S
ARE EXPECTED BY LATE AFTERNOON. WIND DAMAGE IS EXPECTED TO BE THE
MAIN THREAT WITH SEVERE HAIL ALSO POSSIBLE.
..IMY.. 05/21/2011
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