Severe Threat Friday

SPC:::

   DAY 3 CONVECTIVE OUTLOOK  
   NWS STORM PREDICTION CENTER NORMAN OK
   0250 AM CDT WED AUG 01 2007
   
   VALID 031200Z - 041200Z
   
   ...THERE IS A SLGT RISK OF SVR TSTMS OVER THE NERN STATES...
   
   ...NERN STATES...
   
   MID TO UPPER 60S DEWPOINTS WILL LIKELY HAVE ADVECTED NEWD THROUGH
   PRE-FRONTAL WARM SECTOR OVER THE NERN STATES EARLY FRIDAY IN ADVANCE
   OF SHORTWAVE TROUGH THAT WILL EXTEND FROM SERN QUEBEC INTO THE LOWER
   GREAT LAKES AREA. ATTENDANT COLD FRONT SHOULD EXTEND FROM ROUGHLY
   SERN QUEBEC SWWD INTO THE LOWER GREAT LAKES AT START OF THIS PERIOD.
   SLIGHTLY COOLER MID LEVEL TEMPERATURES WITH -10C AT 500 MB WILL
   SPREAD EWD OVER THE WARM SECTOR WITH 6.5 C/KM MID LEVEL LAPSE RATES
   AND MODERATE INSTABILITY EXPECTED BY AFTERNOON. STORMS WILL LIKELY
   DEVELOP AND INTENSIFY ALONG SEWD ADVANCING FRONT AS THE ATMOSPHERE
   DESTABILIZES. PRIMARY LOW LEVEL JET WILL SHIFT NE OF REGION WITHIN
   ZONE OF STRONGER HEIGHT FALLS. HOWEVER...BELT OF WLY 25-35 KT FLOW
   IN THE 700-500 MB LAYER WILL SPREAD OVER MUCH OF NEW ENGLAND ALONG
   SRN PERIPHERY OF EWD ADVANCING UPPER TROUGH. UNIDIRECTIONAL SHEAR
   AROUND 20 TO 30 KT WILL BE SUPPORTIVE OF MULTICELLS. HOWEVER...SOME
   STORMS MAY EVOLVE INTO LINE SEGMENTS AND CLUSTERS WITH AN INCREASING
   THREAT OF MAINLY DAMAGING WIND AS THE BOUNDARY LAYER DESTABILIZES.
   STRONGER STORMS COULD ALSO PRODUCE MARGINALLY SEVERE HAIL.

NWS:::

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TAUNTON MA
338 AM EDT WED AUG 1 2007

.LONG TERM /THURSDAY NIGHT THROUGH TUESDAY/...
-- Changed Discussion --
A COLD FRONT WILL APPROACH FROM THE WEST FRIDAY AFTERNOON. THE
AIRMASS IS EXPECTED TO BECOME INCREASINGLY UNSTABLE ALONG AND AHEAD
OF THIS FRONT. 850 MILLIBAR TEMPERATURES AROUND 20C WITH FULL
MIXING UP THE DRY ADIABAT TO 800 MILLIBARS SUPPORTS HIGHS IN
THE MID 90S. A HEAT ADVISORY MAY NEED TO BE POSTED AS HEAT
INDICES APPROACH OR EXCEED 100 DEGREES FOR A TIME FRIDAY AFTERNOON.
VERTICAL PROFILES INDICATE CAPES RISING TO 2500 J/KG WITH TOTAL
TOTALS IN THE MID 50S. THE REAR RIGHT QUADRANT OF THE 250 MILLIBAR
JET WILL CROSS LOCATIONS NEAR OR JUST NORTH OF THE COUNTY WARNING
AREA. WIND FIELDS AND VERTICAL WIND SHEAR (HELICITY VALUES) ARE NOT
TOO IMPRESSIVE...WITH MAXIMUM SPEEDS OF ABOUT 50 KT AT THE 250
MILLIBAR LEVEL. HOWEVER IF UPDRAFTS CAN REACH THE EQUILIBRIUM LEVEL
GIVEN IMPRESSIVE LOW LEVEL INSTABILITY AND THE APPROACHING
COLD FRONT...DAMAGING WIND GUSTS AND LARGE HAIL WILL LIKELY OCCUR.
IN ADDITION PRECIPITABLE WATER VALUES CLIMBING TO 2.2 G/KG DURING
THE AFTERNOON WOULD ALLOW FOR SOME HEAVY DOWNPOURS. THE STORMS
PREDICTION CENTER CONTINUES TO HAVE INTERIOR PORTIONS OF THE
FORECAST AREA OUTLOOKED FOR FRIDAY DAY THREE.

OVERALL WILL BOOST TEMPERATURES BUT MAINTAIN HIGH CHANCE POPS FRIDAY
AFTERNOON ACROSS THE INTERIOR. WILL CONTINUE TO HIGHLIGHT THE SEVERE
WEATHER RISK IN THE HAZARDOUS WEATHER OUTLOOK.

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Overall, looking at excellent potential. GFS Ensembles have good agreement on near perfect timing of storm passage. NAM forecast lifted indices range between -6 and -10 across New England and even the GFS (which usually underestimates) forecasts -4 to -8. With the SPC already specifying a 30% area, count on a moderate risk for day 2 tomorrow if everything continues.