Thursday Severe Threat: SPC Outlook

DAY 3 CONVECTIVE OUTLOOK  
   NWS STORM PREDICTION CENTER NORMAN OK
   0240 AM CDT TUE JUL 03 2007
   
   VALID 051200Z - 061200Z
   
   ...THERE IS A SLGT RISK OF SVR TSTMS OVER NEW ENGLAND AND THE MID
   ATLANTIC STATES SWWD ALONG THE OH RIVER...
   
   ...SYNOPSIS...
   
   HEIGHT FALLS ATTENDANT TO STRONG SHORT WAVE TROUGH AND ASSOCIATED
   MID/UPPER-LEVEL JET STREAKS DIGGING SEWD INTO THE GREAT LAKES WILL
   SUPPORT FURTHER AMPLIFICATION AND A GRADUAL EWD SHIFT TO LONG WAVE
   TROUGH IN PLACE ACROSS ERN PARTS OF CANADA AND THE UNITED STATES. 
   IN THE LOW-LEVELS...SURFACE COLD FRONT WILL PUSH EWD THROUGH HUDSON
   VALLEY AND MUCH OF NEW ENGLAND WITH SWRN EXTENSION OF FRONT PUSHING
   MORE SLOWLY SWD THROUGH THE OH AND MID MS RIVER VALLEYS.
   
   ...NEW ENGLAND AND THE MID ATLANTIC STATES SWWD ALONG THE OH
   RIVER...
   
   DESPITE PERSISTENT LOW-LEVEL RIDGING OVER THE SRN APPALACHIANS AND
   ADJACENT PIEDMONT AND COASTAL PLAIN...WSWLY LOW-LEVEL FLOW AHEAD OF
   COLD FRONT WILL ADVECT AN INCREASINGLY MOIST BOUNDARY LAYER
   ORIGINATING OVER THE OH VALLEY EWD/NEWD INTO THE MID ATLANTIC STATES
   AND NEW ENGLAND.  THIS MOISTURE COUPLED WITH SOME STEEPENING OF
   LOW-LEVEL LAPSE RATES DUE TO DAYTIME HEATING WILL RESULT IN THE
   DEVELOPMENT OF AT LEAST POCKETS OF MODERATE INSTABILITY AHEAD OF
   FRONT OVER NEW ENGLAND SWWD INTO THE DELMARVA.  RICHER BOUNDARY
   LAYER MOISTURE WILL SUPPORT COMPARATIVELY STRONGER INSTABILITY OVER
   THE SRN OH VALLEY.
   
   TSTMS ARE LIKELY TO BE ONGOING ALONG FRONT THURSDAY MORNING WITH A
   GRADUAL INCREASE IN COVERAGE AND INTENSITY EXPECTED THROUGH THE DAY
   AS INFLOW AIR MASS DESTABILIZES.  THE STRONGEST DEEP LAYER WIND
   FIELDS ARE FORECAST OVER THE HUDSON VALLEY AND NEW ENGLAND SWD INTO
   THE MIDDLE ATLANTIC STATES...IN CONCERT WITH THE STRONGEST MID-LEVEL
   HEIGHT FALLS.  HERE POTENTIAL WILL EXIST FOR AN ORGANIZED CONVECTIVE
   LINE WITH EMBEDDED LEWP/BOW STRUCTURES WITH THE PRIMARY THREAT BEING
   DAMAGING WINDS.  SEVERE PROBABILITIES MAY NEED TO BE INCREASED
   ACROSS PARTS OF THE REGION IN LATER OUTLOOKS ONCE DEGREE OF
   INSTABILITY BECOMES MORE CERTAIN.
   
   ADDITIONAL STRONG TO SEVERE STORMS WILL BE POSSIBLE SWWD ALONG COLD
   FRONT INVOF THE OH RIVER.  WHILE INSTABILITY IS EXPECTED TO BE
   STRONGER...STRONGEST FORCING FOR ASCENT AND VERTICAL SHEAR WILL
   REMAIN NE OF THIS AREA.  THE STRONGEST STORMS WILL REMAIN CAPABLE OF
   SEVERE HAIL AND DAMAGING WINDS GIVEN THE DEGREE OF ANTICIPATED
   INSTABILITY.

Still looking out for a tornado threat in parts of eastern NY into western New England. Instability will be marginal, with vertical shear more than adequate for supercell development. The SPC will likely bump part of the 15% area up to 30% tomorrow, possibly even up to moderate risk criteria on the day 1 outlook. Overall, Thursday is a potentially dangerous day for the Northeast.