SWODY1
SPC AC 181954
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0254 PM CDT SUN MAY 18 2008
VALID 182000Z - 191200Z
...THERE IS A SLGT RISK OF SVR TSTMS ACROSS PARTS OF THE TN
VALLEY...
...TN VALLEY TO SRN APPALACHIANS...
DESPITE WEAK MID LEVEL LAPSE RATES LOCATED ACROSS THE TN VALLEY TO
THE SRN APPALACHIANS...SURFACE DEWPOINTS IN THE 50S TO AROUND 60
COMBINED WITH SURFACE HEATING ARE SUPPORTING WEAK TO MODERATE
INSTABILITY. A FEW TSTMS HAVE DEVELOPED WITHIN THIS ENVIRONMENT
ACROSS SRN MIDDLE TN...BUT THE WEAK MID LEVEL LAPSE RATES AND
WARMING MID LEVEL TEMPERATURES APPEAR TO BE LIMITING THE UPDRAFT
STRENGTH THUS FAR. ADDITIONAL TSTMS WILL BE POSSIBLE AS THE COLD
FRONT MOVES THROUGH THIS REGION INTO THE EVENING. NWLY MID LEVEL
WINDS/DEEP LAYER SHEAR WILL CONTINUE TO INCREASE AS STRONGER
UPSTREAM FLOW TRANSLATES SEWD INTO THE TN VALLEY. THIS COMBINED
WITH THE AVAILABLE INSTABILITY MAY PROVE SUFFICIENT IN PRODUCING
STRONG TO SEVERE TSTMS. FOR THIS REASON...THE 20Z DAY 1 OUTLOOK
WILL MAINTAIN THE SLIGHT RISK AREA.
...MID ATLANTIC REGION...
WEAK MID LEVEL LAPSE RATES AND POCKET OF LOWER SURFACE DEWPOINTS
/UPPER 40S TO LOWER 50S/ ADVECTING NEWD INTO NC/VA APPEAR TO HAVE
LIMITED THE DEVELOPMENT OF STRONGER INSTABILITY THIS AFTERNOON.
THIS IS EVIDENT IN SATELLITE IMAGERY SHOWING A LACK OF EXTENSIVE CU
FORMATION THUS FAR ACROSS FAR SERN VA SWWD TO SC. REGIONAL RADARS/
LIGHTNING DATA INDICATED A BAND OF TSTMS OVER WRN NC WHICH FORMED
ALONG A PRE-FRONTAL TROUGH. EFFECTIVE BULK SHEAR OF 40-50 KT WOULD
SUPPORT A FEW ORGANIZED STORMS...BUT THE WEAK INSTABILITY IS
EXPECTED TO LIMIT UPDRAFT STRENGTH AND THE OVERALL SEVERE WEATHER
THREAT.
FARTHER N ACROSS NRN MD INTO PA...REGIONAL RADARS SHOWED LOW-TOPPED
CONVECTION GENERALLY LOCATED ALONG THE EWD MOVING COLD FRONT. COLD
MID LEVEL TEMPERATURES /AOB -20C AT H5/ AND STRONGER FORCING FOR
ASCENT WITH A NY/PA SHORT WAVE TROUGH TRACKING ENEWD SHOULD SUPPORT
ADDITIONAL DIURNAL TSTM DEVELOPMENT. WEAK INSTABILITY WILL LIMIT
THE SEVERE POTENTIAL...BUT EFFECTIVE BULK SHEAR OF 35-50 KT OVER SRN
PA MAY SUPPORT A FEW STRONGER TO SEVERE STORMS.
..PETERS.. 05/18/2008
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