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Mesoscale Discussion 1757 |
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MESOSCALE DISCUSSION 1757
NWS STORM PREDICTION CENTER NORMAN OK
0710 PM CDT TUE JUL 26 2011
AREAS AFFECTED...SERN NY...CT...RI...MA...NH...WRN ME
CONCERNING...SEVERE THUNDERSTORM WATCH 687...
VALID 270010Z - 270115Z
THE SEVERE WEATHER THREAT FOR SEVERE THUNDERSTORM WATCH 687
CONTINUES.
THE SVR THREAT ACROSS WW687 WILL BE CONFINED TO TWO SEPARATE
AREAS...(1) WRN MAINE AND (2) SERN NY / SRN CT:
1. WRN MAINE: GRAY ME WSR-88D DATA DEPICT AN ORGANIZED QLCS...WITH
EMBEDDED LEWP AND BOWING STRUCTURES...MOVING EWD AROUND 30 KT. ON
ITS PRESENT TRACK...IT COULD MOVE SLIGHTLY EAST OF WW687 DURING THE
NEXT HOUR OR TWO. THIS ACTIVITY IS BEING SUSTAINED BY STRONG FORCING
OVER THE SRN PERIPHERY OF A MID-LEVEL VORT MAX CENTERED OVER QUEBEC
DESPITE VERY MEAGER INSTABILITY. THIS FORCING...COMBINED WITH 0-6-KM
BULK SHEAR MAGNITUDES AROUND 40 KT /PER GRAY VWP DATA/...COULD HELP
MAINTAIN CONVECTION IN THE NEAR TERM. HOWEVER...IT WILL LIKELY CROSS
A N/S-ORIENTED SFC FRONT SHORTLY. EAST OF THIS FEATURE...MLCAPE
BECOMES VERY MINIMAL OWING TO THE INLAND ADVECTION OF THE STABLE
MARINE LAYER EAST OF THE BOUNDARY. HOWEVER...THE DEVELOPMENT OF A
COLD POOL IN THE WAKE OF THE QLCS...MARKED BY SFC PRESSURE RISES OF
2-3 MB WITHIN 2 HOURS OVER PORTIONS OF NRN VT/NH...COULD SUPPORT
SOME CONVECTIVE SUSTENANCE AND A MARGINAL SVR WIND THREAT
IMMEDIATELY TO THE EAST OF WW687 IN MAINE. HOWEVER...THE BRIEF
SPATIOTEMPORAL NATURE OF THIS THREAT WILL PRECLUDE THE NEED FOR ANY
ADDITIONAL WW OR WW EXTENSION.
2. SERN NY / SRN CT...SCATTERED MULTICELLULAR CONVECTION OVER THE
SRN FRINGES OF THE AFOREMENTIONED REGION OF ASCENT WILL CONTINUE
DURING THE NEXT HOUR OR TWO...AS MODERATE DEEP-LAYER SHEAR REMAINS
OVER THE REGION. RELATIVELY STEEPER LOW-LEVEL LAPSE RATES IN THIS
REGION OWING TO PRECONVECTIVE TEMPERATURES IN THE MIDDLE/UPPER 80S
WILL SUPPORT A THREAT FOR GUSTY WINDS...WITH ISOLATED INSTANCES OF
DMGG WIND GUSTS POSSIBLE. THIS ACTIVITY COULD APPROACH THE NEW YORK
CITY METRO AREA BY 01Z...THOUGH STABILIZATION OWING TO NOCTURNAL
COOLING WILL LIKELY COMMENCE THEREAFTER AND MITIGATE THE SVR THREAT.
ELSEWHERE ACROSS WW687...THE LACK OF STRONGER FORCING OR GREATER
INSTABILITY WILL LIKELY MINIMIZE THE SVR THREAT. BASED ON CURRENT
TRENDS...VALID PORTIONS OF WW687 WILL LIKELY BE ALLOWED TO EXPIRE ON
TIME AT 02Z.
..COHEN.. 07/27/2011
ATTN...WFO...CAR...GYX...BOX...BTV...OKX...ALY...
LAT...LON 43706972 41537105 40887276 41097446 41827352 44577157
45637061 45536888 43706972
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