SWODY1
SPC AC 061627
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1127 AM CDT MON SEP 06 2010
VALID 061630Z - 071200Z
...THERE IS A SLGT RISK OF SVR TSTMS THIS AFTERNOON INTO EARLY
TONIGHT FOR IA...SRN MN...AND WRN WI...
...THERE IS A SLGT RISK OF SVR TSTMS FOR TONIGHT FOR THE MIDDLE TX
COAST...
...IA/SRN MN/WRN WI LATE THIS AFTERNOON INTO EARLY TONIGHT...
A STRONG MIDLEVEL SHORTWAVE TROUGH WILL MOVE ENEWD FROM THE CENTRAL
HIGH PLAINS TO THE UPPER MS VALLEY BY TONIGHT. A REMNANT LEE
CYCLONE IN E CENTRAL NEB WILL DEVELOP NNEWD TO SW AND W CENTRAL MN
BY TONIGHT AS THE CYCLONE OCCLUDES...WHILE A TRAILING COLD FRONT
SWEEPS EWD ACROSS IA/WI AND SEWD ACROSS NW MO/KS/NRN OK BY THE END
OF THE PERIOD. THE WARM SECTOR IN ADVANCE OF THE CYCLONE IS
INITIALLY CAPPED BY A VERY WARM EML...ABOVE A MARGINALLY MOIST
BOUNDARY LAYER WITH DEWPOINTS IN THE LOWER 60S. THE MARITIME
TROPICAL AIR MASS STILL RESIDES S OF I-20 IN TX PER SURFACE OBS/GOES
PW IMAGERY AND 12Z SOUNDINGS...AND THE RECENT RUC/NAM FORECASTS OF
68-70 F DEWPOINTS INTO IA THIS EVENING APPEAR TOO AGGRESSIVE.
THUS...EXPECT AT BEST MID 60S DEWPOINTS WITH AFTERNOON
EVAPOTRANSPIRATION AND SOME NEWD MOISTURE ADVECTION FROM OK.
THE VERY WARM EML WILL REQUIRE STRONG ASCENT TO ELIMINATE CONVECTIVE
INHIBITION BY LATE AFTERNOON IN A NARROW BAND ALONG THE COLD
FRONT...WHERE MLCAPE COULD APPROACH 1500-2000 J/KG. FORECAST WIND
PROFILES AHEAD OF THE FRONT AND E/SE OF THE SURFACE CYCLONE WILL BE
FAVORABLE FOR SUPERCELLS WITH LARGE CLOCKWISE-TURNING HODOGRAPHS.
DEEP-LAYER SHEAR VECTOR ORIENTATION WILL ALSO FAVOR SEMI-DISCRETE
STORMS FROM IA NWD INTO SRN MN. IT APPEARS THAT THE MARGINAL
LOW-LEVEL MOISTURE AND STRONG CAP WILL LIMIT THE SPATIAL WINDOW OF
OPPORTUNITY FOR SUPERCELLS AND MAKE IT DIFFICULT FOR STORMS TO
SURVIVE MORE THAN A FEW COUNTIES E OF THE FRONT. THUS...WILL
MAINTAIN 5% TORNADO AND 15% HAIL/WIND PROBABILITIES IN AN
ENVIRONMENT THAT COULD OTHERWISE SUPPORT A MORE ROBUST SEVERE STORM
THREAT.
A FEW STORMS MAY DEVELOP SWWD ALONG THE COLD FRONT THIS EVENING FROM
NW MO ACROSS ERN KS INTO N CENTRAL OK. STORM INITIATION WILL DEPEND
ON STRONG LOW-LEVEL ASCENT ALONG THE FRONT AND RELATIVELY DEEP
MIXING FARTHER SW TOWARD NRN OK...AND STORM COVERAGE IS
QUESTIONABLE. IF STORMS FORM...A FEW STRONG WIND GUSTS AND
MARGINALLY SEVERE HAIL WILL BE POSSIBLE FOR A FEW HOURS THIS
EVENING.
...MIDDLE TX COAST TONIGHT...
TROPICAL STORM HERMINE IS FORECAST TO APPROACH HURRICANE STRENGTH
JUST PRIOR TO LANDFALL ALONG THE LOWER TX COAST LATE TONIGHT /SEE
LATEST NHC ADVISORIES FOR DETAILS/. DEEPENING OF THE CYCLONE WILL
RESULT IN A CORRIDOR OF INCREASING LOW-LEVEL FLOW/SHEAR TO THE RIGHT
OF THE CYCLONE CENTER...WHICH WILL OVERSPREAD THE MIDDLE TX COAST
OVERNIGHT. THE CORRIDOR OF INCREASING LOW-LEVEL SHEAR WILL ALSO
COINCIDE WITH MID-UPPER 70S BOUNDARY LAYER DEWPOINTS AND AT LEAST
WEAK SURFACE-BASED INSTABILITY. GIVEN THESE ENVIRONMENTAL
FACTORS...WILL INTRODUCE A SLIGHT RISK AND 5% TORNADO PROBABILITIES
FOR OUTER BAND SUPERCELLS DURING THE OVERNIGHT PERIOD.
..THOMPSON/HURLBUT.. 09/06/2010
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