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DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1226 PM CDT FRI SEP 07 2012
VALID 081200Z - 091200Z
...THERE IS A MDT RISK OF SVR TSTMS FROM NERN MD/NRN DE...NWD INTO
UPSTATE NY/VT/NH...
...THERE IS A SLGT RISK OF SVR TSTMS SURROUNDING THE MDT RISK FROM
THE CAROLINAS INTO WRN ME...
...DAMAGING SEVERE THUNDERSTORMS ARE EXPECTED ACROSS THE
NORTHEASTERN U.S. SATURDAY...
POTENTIALLY SIGNIFICANT DAMAGING WIND EVENT IS EXPECTED ACROSS MUCH
OF THE NERN U.S. SATURDAY. LATEST MODEL GUIDANCE...ESPECIALLY THE
NAM/ECMWF...SUGGEST SHORT-WAVE TROUGH OVER THE UPPER GREAT LAKES
WILL DIG INTO LOWER MI BY 08/12 BEFORE EJECTING NEWD IN A NEGATIVELY
TILTED FASHION AND DEEPENING OVER SERN ONTARIO/WRN QUEBEC. 90-120M
12HR HEIGHT FALLS WILL SPREAD ACROSS WRN/UPSTATE NY DURING THE DAY
ENSURING A STRONGLY FORCED AND CONVECTIVELY-ACTIVE COLD FRONT. THIS
EVOLUTION SUGGESTS A FRONTAL INTRUSION THAT WILL INDUCE A BAND OF
SEVERE THUNDERSTORMS AS IT SURGES ACROSS THE NRN MIDDLE ATLANTIC
REGION INTO NEW ENGLAND.
ALL INDICATIONS FAVOR A SQUALL ALONG THE WIND SHIFT AT SUNRISE FROM
SRN ONTARIO SWD ACROSS OH...TRAILING INTO THE TN VALLEY. THIS
ACTIVITY IS EXPECTED TO INTENSIFY AS IT MOVES INTO WRN
NY/PA...ESPECIALLY BY 18Z AS BOUNDARY LAYER BEGINS TO WARM.
ALTHOUGH FORECAST LAPSE RATES ARE NOT PARTICULARLY STEEP BOUNDARY
LAYER AIRMASS IS FAIRLY MOIST ATTM WITH UPPER 60S-70F SFC DEW POINTS
IN PLACE ACROSS THE MIDDLE ATLANTIC REGION. THERE IS LITTLE REASON
TO BELIEVE THIS AIRMASS WILL NOT SPREAD NWD ACROSS PA/NJ INTO
UPSTATE NY AHEAD OF THE COLD FRONT AND AMPLE MOISTURE/INSTABILITY
WILL SPREAD NWD TOWARD THE CANADIAN BORDER TO SUPPORT ROBUST
UPDRAFTS WITHIN A STRONGLY SHEARED ENVIRONMENT.
OF PARTICULAR CONCERN IS THE EXPECTED MID LEVEL JET THAT SHOULD
INTENSIFY AS IT EJECTS ACROSS WRN PA TO SPEEDS IN EXCESS OF 70KT
OVER UPSTATE NY BY 09/00Z. WITH DEEPENING SFC LOW OVER SERN ONTARIO
FORECAST SHEAR PROFILES BECOME QUITE FAVORABLE FOR SUSTAINING
ORGANIZED UPDRAFTS. WHILE A DAMAGING SQUALL LINE IS EXPECTED ALONG
THE ADVANCING COLD FRONT...ENVIRONMENTAL SHEAR WILL BECOME QUITE
FAVORABLE FOR PRE-FRONTAL SUPERCELLS AND EMBEDDED SUPERCELLS WITHIN
THE MAIN SQUALL LINE. FORECAST SOUNDINGS FROM NRN NJ NWD THROUGH
THE HUDSON VALLEY SUGGEST TORNADOES ARE POSSIBLE IF DISCRETE
SUPERCELLS CAN EVOLVE AHEAD OF THE MAIN LINE AND WITH CIRCULATIONS
WITHIN THE LINE. LATEST MODEL GUIDANCE SUGGESTS THE BACK EDGE OF
THE PRIMARY SQUALL LINE WILL ADVANCE INTO THE HUDSON VALLEY BY LATE
AFTERNOON TRAILING SWWD INTO CNTRL VA BY 09/00Z WITH SUBSEQUENT
MOVEMENT ACROSS MUCH OF NEW ENGLAND BY 06Z.
...SERN U.S...
NWLY FLOW IS EXPECTED TO DEEPEN ACROSS THE TN VALLEY/NRN GULF STATES
DURING THE DAY2 PERIOD AS MAIN UPPER TROUGH/FORCING SHIFT ACROSS
SERN CANADA/NERN U.S. THIS WILL ALLOW A FAIRLY PRONOUNCED COLD
FRONT TO SPREAD ACROSS THE SERN U.S./GULF STATES DURING THE
AFTERNOON. ISOLATED SEVERE THUNDERSTORMS MAY BE NOTED WITH
CONVECTION THAT DEVELOPS ALONG/AHEAD OF THE BOUNDARY BUT DEEP LAYER
SHEAR/FORCING APPEAR A BIT INADEQUATE TO WARRANT MORE THAN 5 PERCENT
SEVERE PROBS ATTM.
..DARROW.. 09/07/2012
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