MESOSCALE DISCUSSION 1074

MESOSCALE DISCUSSION 1074
NWS STORM PREDICTION CENTER NORMAN OK
1035 AM CDT TUE JUN 22 2010

AREAS AFFECTED...WRN/CENTRAL PA...MD...PARTS OF ERN WV...NRN/ERN VA

CONCERNING...SEVERE POTENTIAL...WATCH POSSIBLE

VALID 221535Z - 221600Z

WW IS BEING CONSIDERED FOR PARTS OF WRN/CENTRAL PA SWD THROUGH MD...PARTS OF ERN WV AND NRN/ERN VA.

SHORTWAVE TROUGH...CURRENTLY TRACKING EWD INTO THE LOWER GREAT LAKES/UPPER OH VALLEY PER WATER VAPOR IMAGERY...WILL MOVE EWD INTO NY/PA AND NRN VA/MD THIS AFTERNOON. 12Z UPPER AIR DATA INDICATED 40 KT WLY MIDLEVEL FLOW WITHIN THE BASE OF THIS TROUGH OVER OH. OBJECTIVE ANALYSES SHOWED EFFECTIVE BULK SHEAR ALREADY INCREASING ACROSS CENTRAL PA TO NRN VA AS THE STRONGER FLOW ALOFT SPREADS EWD. IN THE LOW LEVELS...SURFACE FRONT ATTENDANT TO THE SHORTWAVE TROUGH EXTENDED SSWWD FROM SWRN ONTARIO THROUGH CENTRAL OH. THIS BOUNDARY WILL CONTINUE EWD TODAY AND MARK THE WRN EXTENT OF THE SEVERE WEATHER THREAT.

CLOUDINESS/FILTERED SUNSHINE ACROSS PA...ASSOCIATED WITH CIRRUS AND LEADING BAND OF ONGOING CONVECTION OVER CENTRAL PA TO THE ERN WV PANHANDLE IS LIMITING SURFACE HEATING SOME THIS MORNING. THIS COMBINED WITH WEAK MIDLEVEL LAPSE RATES APPEARS TO BE RESULTING IN A SLOWER DESTABILIZATION OF THE AIR MASS THUS FAR. HOWEVER... FURTHER DIABATIC HEATING WITHIN A MOIST AIR MASS IS EXPECTED TO SUPPORT AT LEAST MODERATE INSTABILITY BY THIS AFTERNOON WITH MLCAPE 1000-1500 J/KG EXTENDING FROM OH INTO CENTRAL PA AND SWD TO VA/MD.

12Z WRF-HRRR SUGGESTED THE ONGOING STORMS OVER CENTRAL PA TO ERN WV PANHANDLE WILL CONTINUE TO WEAKEN...WITH NEW TSTMS DEVELOPING OVER WRN PA TO WV AROUND 17Z AS THE FRONT MOVES EWD. MODERATE INSTABILITY AND EFFECTIVE BULK SHEAR UP TO 40 KT WILL SUPPORT ORGANIZED STORMS WITH A THREAT OF HAIL...STRONG WIND GUSTS AND A POTENTIAL TORNADO THREAT. THE TORNADO THREAT WILL BE GREATER IN ANY LOCATION WHERE LOW LEVEL WINDS ARE MORE SLY...HENCE INCREASING LOW LEVEL DIRECTIONAL SHEAR. GREATEST TORNADO THREAT SHOULD BE EAST OF THE MOUNTAINS. HOWEVER...FORECAST SOUNDINGS SUGGEST SURFACE WINDS
AHEAD OF THE FRONT IN WRN PA WILL REMAIN FAVORABLY BACKED TO SUPPORT A TORNADO THREAT WITH INITIAL ACTIVITY PRIOR TO WINDS VEERING WITH
FRONTAL PASSAGE.

..PETERS.. 06/22/2010