SWODY1
SPC AC 201621
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1121 AM CDT SAT JUN 20 2009
VALID 201630Z - 211200Z
...THERE IS A SLGT RISK OF SVR TSTMS IN THE MID-ATLANTIC STATES...
...THERE IS A SLGT RISK OF SVR TSTMS OVER PARTS OF THE CENTRAL
PLAINS...
...MID ATLANTIC REGION...
STRONG UPPER TROUGH/VORTICITY CENTER IS WELL-DEFINED ON WATER VAPOR
IMAGERY MOVING EWD ACROSS WRN PA. FORCING FOR LARGE SCALE ASCENT IN
ADVANCE OF THE SYSTEM IS GENERATING A COMMA-SHAPED REGION OF CLOUDS
AND CONVECTION ARCING FROM SRN NY ACROSS NJ AND INTO THE DELMARVA
REGION. RELATIVELY CLEAR SKIES OVER SOUTH CENTRAL/SERN VA AND
ADJACENT PARTS OF NC HAVE ALLOWED STRONG DIABATIC HEATING TO OCCUR
WITH SURFACE TEMPERATURES IN THE UPPER 80S-LOWER 90S. AMPLE
LOW-LEVEL MOISTURE PERSISTS OVER THE AREA WITH SURFACE DEW POINTS
GENERALLY IN THE LOWER 70S...CONTRIBUTING TO MLCAPE OF 1000-2000
J/KG /DESPITE WEAK MID-LEVEL LAPSE RATES/. FARTHER NORTH...IN THE
WAKE OF THE CONVECTIVE BAND...BREAKS IN CLOUD COVER ARE EVIDENT FROM
WRN VA INTO SOUTH CENTRAL PA AHEAD OF THE ADVANCING SURFACE COLD
FRONT. THIS SHOULD PERMIT LOCALIZED AREAS OF HEATING AND
DESTABILIZATION TO OCCUR.
NEW CONVECTION IS CURRENTLY DEVELOPING OVER PARTS OF ERN WV INTO
EXTREME SWRN VA ALONG THE LEADING EDGE OF THE MID/UPPER LEVEL DRY
INTRUSION NOTED IN WATER VAPOR IMAGERY. THIS ACTIVITY IS LOCATED
ALONG THE WRN EDGE OF THE INSTABILITY GRADIENT WITHIN A BAND OF
40-50 KT WNWLY MID LEVEL FLOW ALOFT...AND WILL BE MONITORED FOR
SIGNS OF INTENSIFICATION AS IT MOVES ESEWD THIS AFTERNOON INTO AN
INCREASINGLY UNSTABLE ENVIRONMENT. IF THE STORMS CAN PERSIST AND
MOVE EAST OF THE HIGHER TERRAIN...30-40 KT DEEP LAYER SHEAR WILL
PROMOTE ORGANIZED STORM STRUCTURES INCLUDING BOW ECHOES AND ISOLATED
SUPERCELLS...WITH ASSOCIATED THREAT FOR DAMAGING WIND GUSTS AND
LARGE HAIL. AN ISOLATED TORNADO OR TWO MAY ALSO BE POSSIBLE.
ADDITIONAL STRONG/SEVERE STORMS MAY ALSO DEVELOP CLOSER TO THE
VORTICITY MAX FROM THE DELMARVA INTO SERN PA/SRN NJ...ALTHOUGH THE
COVERAGE OF STORMS WILL BE DEPENDENT ON THE DEGREE OF
DESTABILIZATION.
...CENTRAL PLAINS...
SCATTERED STORMS WILL CONTINUE DEVELOPING WITHIN PLUME OF DEEP
SUBTROPICAL MOISTURE THAT WILL PERSIST ALONG WRN PERIPHERY OF UPPER
RIDGE. LOW-MID LEVEL FLOW WILL INCREASE DURING THE AFTERNOON IN
ASSOCIATION WITH SHORTWAVE TROUGH EJECTING NEWD THROUGH CNTRL HIGH
PLAINS. HODOGRAPH SIZE WILL INCREASE AND BECOME FAVORABLE FOR A
THREAT OF LOW LEVEL MESOCYCLONES AND POSSIBLY ISOLATED
TORNADOES...ESPECIALLY WHERE THE LOW LEVEL JET INTERSECTS THE
FRONTAL BOUNDARY ACROSS KS. A LIMITING FACTOR WILL BE EXPECTED
MARGINAL THERMODYNAMIC ENVIRONMENT CHARACTERIZED BY WEAK INSTABILITY
AND MARGINAL LAPSE RATES.
...GREAT BASIN THROUGH NRN ROCKIES...
VERTICAL SHEAR WILL INCREASE IN ASSOCIATION WITH SHORTWAVE TROUGH
EJECTING NEWD FROM THE GREAT BASIN INTO THE NRN ROCKIES. MOIST
PROFILES AND LARGE SCALE ASCENT AHEAD OF THIS FEATURE WILL LIKELY
PROMOTE THE DEVELOPMENT OF NUMEROUS STORMS DURING THE AFTERNOON.
ISOLATED STORMS COULD BECOME CAPABLE OF PRODUCING STRONG WIND GUSTS
AND MARGINALLY SEVERE HAIL.
..WEISS/GARNER.. 06/20/2009
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