Between a persistent western Atlantic high pressure system and a strong cold front increasingly southwest winds are transporting a hot, humid tropical like and unstable air mass into the area, the cold front will sweep southeast this afternoon, and the clash of a strong polar air mass associated with the front, and the unstable air mass ahead of the front lines of strong to severe storms are likely to fire up between mid afternoon and this evening
AREAS AFFECTED…NEW ENGLAND INTO ERN PA/NRN NJ
CONCERNING…SEVERE POTENTIAL…WATCH LIKELY
VALID 061631Z – 061800Z
PROBABILITY OF WATCH ISSUANCE…80 PERCENT
SUMMARY…BROKEN BANDS OF STRONG TO SEVERE THUNDERSTORMS WILL
DEVELOP THIS AFTERNOON AHEAD OF A COLD FRONT AND TRACK E/NE ACROSS
ERN PA/NRN NJ INTO NEW ENGLAND. DAMAGING WINDS WILL BE THE MAIN
THREAT WITH THESE STORMS. A WATCH WILL LIKELY BE NEEDED WITHIN THE
NEXT 1-2 HOURS.
DISCUSSION…TEMPERATURES HAVE WARMED INTO THE 80S EARLY THIS
AFTERNOON IN BROKEN CLOUDINESS AHEAD OF THE SFC COLD
FRONT…RESULTING IN MODERATE DESTABILIZATION /MLCAPE APPROACHING
2000 J/KG/ OF THE VERY MOIST BOUNDARY LAYER /LOW 70S DEWPOINTS/.
AREAS OF AGITATED CUMULUS WERE EVIDENT ON LATEST VIS SATELLITE
IMAGERY FROM CENTRAL PA NEWD INTO NEW ENGLAND IN THE VICINITY WEAK
SFC CONFLUENCE ZONES. THUNDERSTORMS ARE EXPECTED TO DEVELOP OVER THE
NEXT HOUR OR SO IN THE VICINITY OF THIS MODEST SFC CONVERGENCE AHEAD
OF THE MAIN COLD FRONT FROM ERN PA INTO S NY/N NJ. EFFECTIVE SHEAR
AROUND 30-40 KT WILL BE ADEQUATE FOR SOME ORGANIZED STORM
CLUSTERS/LINE SEGMENTS. WHILE MIDLEVEL LAPSE RATES WILL REMAIN
POOR…STRONG SFC HEATING HAS RESULTED IN STEEP LOW LEVEL LAPSE
RATES…AND COMBINED WITH PW VALUES AOA 1.75 INCHES…STRONG
/LOCALLY DAMAGING/ WINDS WILL BE POSSIBLE WITH BROKEN BANDS OF
CONVECTION. ADDITIONAL STORMS WILL DEVELOP FURTHER N/NE INTO NEW
ENGLAND ALONG THE COLD FRONT LATER THIS AFTERNOON.
A WATCH WILL LIKELY BE NEEDED IN THE NEXT 1-2 HOURS.
Above is the mesoscale discussion from the storm prediction center stating the increasing severe threat and the need for a severe weather watch
The threat will begin to unfold around 2-3 pm especially for northwest areas and the lines of storms will gradually move east southeast , the threat for strong to severe storms peaks between 4-9pm for the area with the biggest threat being damaging winds and large hail, very heavy down pours are also likely with rainfall rates of 1-2 inches per hour likely in the strongest storms
The storm threat will wind down after 9 pm with all rain ending by 1 am.