SWODY1
SPC AC 291245
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0745 AM CDT THU SEP 29 2011
VALID 291300Z - 301200Z
...THERE IS A SLGT RISK OF SVR TSTMS TODAY INTO THIS EVENING FROM
ERN PA/NJ EWD INTO CNTRL/SRN PARTS OF NEW ENGLAND...
...THERE IS A SLGT RISK OF SVR TSTMS TODAY INTO THIS EVENING ACROSS
PORTIONS OF THE UPPER GREAT LAKES AND OH VLY...
...MID-ATLANTIC COAST INTO NEW ENGLAND...
MID/UPPER-LEVEL LOW OVER THE GREAT LAKES AND OH VLY WILL EVOLVE INTO
AN OPEN WAVE TODAY AS EMBEDDED VORTICITY MAXIMUM AND 50-55 KT
MIDLEVEL JET STREAK TRANSLATE FROM THE UPPER OH VLY INTO NEW
ENGLAND. IN THE LOW LEVELS...WEAK FRONTAL WAVE OBSERVED OVER NERN
PA WILL DEVELOP NNEWD THROUGH THE HUDSON VLY WHILE TRAILING PORTION
OF COLD FRONT ADVANCES EWD TO OFF THE MID-ATLANTIC COAST...AND
THROUGH NEW ENGLAND BY 30/12Z. MEANWHILE...A WARM FRONT CURRENTLY
RESIDING ACROSS FAR SERN NY AND SRN NEW ENGLAND WILL LIFT NWD IN
ADVANCE OF COLD FRONT.
DESPITE NUMEROUS CLOUDS AND WEAK LAPSE RATES...THE PRESENCE OF A
MOIST BOUNDARY LAYER AND MODEST DAYTIME HEATING WILL BOOST MLCAPE
VALUES TO 1000-1300 J/KG BY AFTERNOON. WATER VAPOR IMAGERY AND
MODEL DIAGNOSTIC FIELDS SUGGEST THAT THE LEADING EDGE OF STRONGER
FORCING FOR ASCENT IS ALREADY OVERSPREADING THE BLUE RIDGE. AS
SUCH...TSTMS ARE EXPECTED TO INCREASE IN COVERAGE AND INTENSITY BY
LATE MORNING/EARLY AFTERNOON...INITIALLY OVER THE DE AND HUDSON
RIVER VLYS. STEADILY STRENGTHENING MID/HIGH-LEVEL WIND FIELD WILL
RESULT IN 40-50 KT OF DEEP SSWLY SHEAR BY AFTERNOON WHICH WILL BE
MORE THAN SUFFICIENT TO SUPPORT SUPERCELLS AND BOWING STRUCTURES
CAPABLE OF DAMAGING WINDS...SOME LARGE HAIL AND PERHAPS A TORNADO OR
TWO. EXPECT TSTMS TO RAPIDLY SPREAD EWD/NEWD THROUGH SRN AND CNTRL
PARTS OF NEW ENGLAND THIS AFTERNOON INTO TONIGHT WITH A CONTINUED
RISK FOR DAMAGING WINDS AND A TORNADO.
...UPPER GREAT LAKES/OH VALLEY...
VIGOROUS SHORT-WAVE TROUGH AND ATTENDANT 70-90 KT MIDLEVEL JET
STREAK WILL UNDERGO CONSIDERABLE AMPLIFICATION DURING THE D1 PERIOD
WHILE DIGGING SEWD THROUGH THE UPPER GREAT LAKES INTO OH AND TN
VLYS. ASSOCIATED SURFACE COLD FRONT FROM WRN WI TO MID MO VLY WILL
ACCORDINGLY STRENGTHEN WHILE SWEEPING EWD/SEWD TOWARD THE
APPALACHIANS AND GULF COAST STATES.
MOISTURE WILL REMAIN LIMITED AHEAD OF THE COLD FRONT OWING TO THE
PRESENCE OF A MODIFIED CP AIR MASS IN WAKE OF ATLANTIC COAST FRONTAL
SYSTEM. HOWEVER...DAYTIME HEATING AND STEEP MIDLEVEL LAPSE RATES
WILL YIELD AFTERNOON MLCAPE VALUES APPROACHING 500-1000 J/KG.
DEEPENING/STRENGTHENING FRONTAL CIRCULATION COUPLED WITH A CORRIDOR
OF INTENSE DCVA IN ADVANCE OF UPPER TROUGH ARE EXPECTED TO FORCE A
BAND OF TSTMS ALONG THE FRONT THIS AFTERNOON. INCIPIENT
SURFACE-BASED STORM DEVELOPMENT APPEARS MOST PROBABLE FROM PARTS OF
LM AND WRN LOWER MI INTO IND WITH ACTIVITY SPREADING RAPIDLY
EWD/SEWD ACROSS LOWER MI INTO OH BY EVENING. WHILE SOME HAIL AND A
BRIEF TORNADO ARE POSSIBLE...DAMAGING WINDS WILL BE THE PRIMARY
SEVERE WEATHER HAZARD OWING TO THE DOWNWARD MOMENTUM TRANSFER OF A
STRONG...UNIDIRECTIONAL WIND FIELD.
..MEAD/ROGERS.. 09/29/2011
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