SWODY1
SPC AC 081244
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0744 AM CDT TUE SEP 08 2009
VALID 081300Z - 091200Z
...THERE IS A SLGT RISK OF SVR TSTMS THIS AFTERNOON INTO EARLY
TONIGHT FOR THE CENTRAL AND NRN PLAINS...
...NRN AND CENTRAL PLAINS THROUGH TONIGHT...
A MID LEVEL SHORTWAVE TROUGH OVER MT THIS MORNING WILL ROTATE
EWD/NEWD OVER THE DAKOTAS LATER TODAY INTO TONIGHT...AROUND THE SERN
PERIPHERY OF THE LARGER-SCALE CLOSED LOW NOW OVER NRN ALBERTA. THIS
SHORTWAVE TROUGH WILL BE PRECEDED BY A SURFACE COLD FRONT THAT WILL
MOVE EWD ACROSS CENTRAL SD AND ERN ND TODAY...AND ERN SD/NW MN LATE
TONIGHT. THE COLD FRONT WILL ALSO PROGRESS SWD ACROSS WRN NEB LATE
TODAY AND NE CO/NW KS TONIGHT.
A LEAD MID LEVEL IMPULSE AND AN ASSOCIATED/WEAKENING THUNDERSTORM
CLUSTER WILL MOVE NEWD OVER NE ND AND NW MN THIS MORNING. THERE IS
SOME CONCERN THAT RESIDUAL CLOUDS WITH THE ONGOING ND STORMS...AS
WELL AS OTHER WAA STORMS OVER NE SD/SE ND...COULD INTERFERE WITH
SURFACE HEATING/DESTABILIZATION TODAY INVOF OF FAR NW MN AND EXTREME
E CENTRAL ND. THE POTENTIAL FOR DESTABILIZATION IS GREATER FARTHER
TO THE S ACROSS SD/NEB WHERE A BELT OF LOW-MID 60S BOUNDARY LAYER
DEWPOINTS IS LOCATED E OF THE COLD FRONT...BENEATH A PLUME OF STEEP
MID LEVEL LAPSE RATES OVER THE PLAINS. DAYTIME HEATING/MIXING AND
LOW-LEVEL ASCENT ALONG THE COLD FRONT WILL REMOVE CONVECTIVE
INHIBITION AND SUPPORT THUNDERSTORM DEVELOPMENT BY MID-LATE
AFTERNOON...WITH A BROKEN BAND OF STORMS EXPECTED ALONG THE LENGTH
OF THE FRONT BY THIS EVENING. THOUGH THE STRONGER DEEP LAYER FLOW
WILL REMAIN LARGELY ON THE COOL SIDE OF THE SURFACE FRONT...THERE
COULD BE A NARROW CORRIDOR ALONG THE FRONT WITH SUFFICIENT VERTICAL
SHEAR FOR BOWING SEGMENTS AND MARGINAL SUPERCELL STRUCTURES...GIVEN
AFTERNOON MLCAPE VALUES AOA 2000 J/KG. THE PRIMARY SEVERE THREATS
WILL BE ISOLATED DAMAGING WINDS AND LARGE HAIL FROM THIS AFTERNOON
INTO AT LEAST EARLY TONIGHT.
...SRN KS/NRN OK TODAY INTO TONIGHT...
A CONVECTIVELY ENHANCED MID LEVEL WAVE OVER CENTRAL KS WILL LIKELY
DRIFT ESEWD TOWARD S CENTRAL KS AND N CENTRAL/NE OK TODAY. ONGOING
CONVECTION WITH THIS SYSTEM IS BEING AUGMENTED BY LOW-LEVEL WAA AND
MOISTURE TRANSPORT ON THE NOSE OF A 35 KT LLJ. SOME WEAKENING OF
THE LLJ IS EXPECTED DURING THE DAY AND THE COVERAGE OF THUNDERSTORMS
WILL LIKELY DECREASE BY ABOUT MIDDAY. HOWEVER...DIFFERENTIAL
HEATING ALONG THE SRN FRINGE OF THE RESIDUAL CONVECTIVE CLUSTER AND
ASSOCIATED OUTFLOW MAY SUPPORT ADDITIONAL THUNDERSTORM DEVELOPMENT
THIS AFTERNOON INTO NRN OK...WHERE ISOLATED HAIL AND/OR DOWNBURST
WINDS WILL BE POSSIBLE. OVERNIGHT...THE SLY LLJ WILL AGAIN INCREASE
AND MAY ALLOW ELEVATED CONVECTION TO DEVELOP AGAIN IN ROUGHLY THE
SAME CORRIDOR.
...TN/KY/OH/SE INDIANA TODAY...
THE WEAK MID LEVEL LOW NOW CENTERED OVER CENTRAL INDIANA WILL DRIFT
ESEWD TOWARD NE KY THROUGH TONIGHT. DAYTIME HEATING AROUND THE
ERN/SRN FRINGES OF THE MID LEVEL CIRCULATION AND COOLER MID LEVEL
TEMPERATURES WILL RESULT IN AFTERNOON MLCAPE VALUES OF 500-1000
J/KG...AND THE POTENTIAL FOR SCATTERED THUNDERSTORMS.
STILL...VERTICAL SHEAR WILL REMAIN WEAK OVER THIS AREA WITH THE
SOMEWHAT MARGINAL INSTABILITY...THUS ANY SEVERE STORM THREAT APPEARS
TOO SMALL TO JUSTIFY AN INTRODUCTION OF WIND OR HAIL PROBABILITIES.
...NC OUTER BANKS TODAY...
THE SURFACE LOW ALONG THE BAROCLINIC ZONE IS LOCATED S OF HAT AS OF
12Z. SHORT TERM MODEL FORECASTS AND EXTRAPOLATION OF OBSERVED DATA
SUGGEST THAT THE LOW WILL PROGRESS SLOWLY NEWD IN CONJUNCTION WITH A
SHORTWAVE TROUGH PIVOTING NEWD AROUND THE WEAK MID LEVEL LOW OVER
THE OH VALLEY. THIS WILL KEEP THE UNSTABLE WARM SECTOR AND FAVORED
ZONE FOR THUNDERSTORM DEVELOPMENT...AND ANY ASSOCIATED RISK FOR
ROTATING STORMS...JUST OFFSHORE.
..THOMPSON/GARNER.. 09/08/2009
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