MESOSCALE DISCUSSION 1946
   NWS STORM PREDICTION CENTER NORMAN OK
   1258 PM CDT FRI AUG 21 2009
   
   AREAS AFFECTED...ERN PA...NRN NJ...SERN NY...VT...NH...WRN MA...CT
   
   CONCERNING...SEVERE THUNDERSTORM WATCH 726...727...
   
   VALID 211758Z - 211930Z
   
   THE SEVERE WEATHER THREAT FOR SEVERE THUNDERSTORM WATCH
   726...727...CONTINUES.
   
   THREAT FOR MAINLY ISOLATED DAMAGING WIND AND HAIL WILL PERSIST NEXT
   FEW HOURS FROM THE MID ATLANTIC NEWD INTO A PORTION OF NEW ENGLAND.
   A MODEST INCREASE IN THE ISOLATED TORNADO THREAT IS EXPECTED FROM
   SERN NY THROUGH SRN NEW ENGLAND THIS AFTERNOON. DEPENDING ON
   MESOSCALE/CONVECTIVE TRENDS...A PORTION OF WW 726 MIGHT NEED TO BE
   UPGRADED TO A TORNADO WATCH.
   
   STORMS HAVE INCREASED ALONG AND AHEAD OF DIFFERENTIAL HEATING AND
   CONVERGENCE BOUNDARY FROM ERN PA THROUGH ERN NY AND VT WITH MIXED
   MODES INCLUDING LINES AND SUPERCELLS. THE THICKER CLOUD SHIELD HAS
   DISSIPATED EAST OF ONGOING STORMS ALLOWING THE MOIST BOUNDARY LAYER
   TO WARM INTO THE UPPER 80S...WHICH AS BOOSTED MLCAPE TO AROUND 2500
   J/KG. WIND PROFILES REMAIN LARGELY UNIDIRECTIONAL SWLY...BUT WITH
   DEEP LAYER SHEAR FROM 35 TO 45 KT SUPPORTIVE OF SUPERCELLS AND
   BOWING SEGMENTS. SUPERCELL MOVING INTO ULSTER COUNTY APPEARS TO BE
   MOVING ALONG OUTFLOW BOUNDARY LEFT EMANATING FROM STORMS FARTHER
   EAST.
   
   WV IMAGERY SHOWS AN IMPULSE LIFTING RAPIDLY NEWD THROUGH ERN OH/WRN
   PA...WEST OF THE UNSTABLE WARM SECTOR. HOWEVER..MODELS CONTINUE TO
   INDICATE A LOW LEVEL RESPONSE OVER SRN NEW ENGLAND WHERE AN INCREASE
   IN THE SWLY LOW LEVEL JET IS FORECAST. THIS WILL LIKELY RESULT IN
   SOME INCREASE IN 0-1 KM HODOGRAPH SIZE WITH TIME AND STORM RELATIVE
   HELICITIES APPROACHING 150-200 M2/S2 ALONG WITH A MODEST INCREASE IN
   ISOLATED TORNADO THREAT...ESPECIALLY IF SOME DISCRETE OR
   SEMI-DISCRETE MODES CAN BE MAINTAINED.
   
   ..DIAL.. 08/21/2009
   
   
   ATTN...WFO...GYX...BOX...BTV...OKX...ALY...PHI...BGM...
   
   LAT...LON   42907354 44477269 44137131 41957189 40797408 39927524
               40117586 41637471 42907354