Tuesday, September 13, 2011

DAY1SVR: Day 1 Convective Outlook

ACUS01 KWNS 131242
SWODY1
SPC AC 131241

DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0741 AM CDT TUE SEP 13 2011

VALID 131300Z - 141200Z

...THERE IS A SLGT RISK OF SVR TSTMS THIS AFTERNOON/EVENING FOR
WRN/NRN NY AND NRN VT...

...WRN/NRN NY TO NRN VT/NH THIS AFTERNOON/EVENING...
A LEAD SHORTWAVE TROUGH NEAR THE ONTARIO/QUEBEC BORDER WILL
ACCELERATE NEWD NEAR AND N OF THE SAINT LAWRENCE VALLEY THROUGH
TONIGHT...WHILE AN ASSOCIATED SURFACE COLD FRONT MOVES SEWD ACROSS
NY/NRN NEW ENGLAND. A BAND OF LOW-MID 60S BOUNDARY LAYER DEWPOINTS
AND AFTERNOON SURFACE TEMPERATURES OF 75-80 F WILL CONTRIBUTE TO
MLCAPE OF 500-1500 J/KG IN ADVANCE OF THE FRONT. WEAKENING
CONVECTIVE INHIBITION DURING THE DAY AND ASCENT ALONG THE FRONT WILL
PROMOTE THE DEVELOPMENT OF ONE OR MORE BANDS OF THUNDERSTORMS ALONG
THE FRONT THIS AFTERNOON ACROSS THE SAINT LAWRENCE VALLEY...WITH
STORMS EXPECTED TO PROGRESS EWD/SEWD INTO NY AND NRN NEW ENGLAND
THIS EVENING. THE COMBINATION OF WEAK-MODERATE INSTABILITY AND
EFFECTIVE BULK SHEAR OF 30-40 KT WILL SUPPORT A RISK OF ORGANIZED
LINE SEGMENTS/EMBEDDED SUPERCELLS CAPABLE OF PRODUCING DAMAGING
WINDS AND AT LEAST MARGINALLY SEVERE HAIL.

...AZ/SE CA TODAY...
THE MIDLEVEL TROUGH OVER SRN CA WILL BEGIN TO DRIFT EWD...WHILE A
DOWNSTREAM MOISTURE PLUME WILL BE MAINTAINED ACROSS SE CA AND AZ.
WEAK SPEED MAXIMA ROTATING THROUGH THE TROUGH AND THE INFLUX OF
MOISTURE ARE SUPPORTING THUNDERSTORMS ALREADY THIS MORNING IN SRN
CA/SRN NV/NW AZ...AND ADDITIONAL DEVELOPMENT IS EXPECTED DURING THE
DAY WITH SURFACE HEATING/DESTABILIZATION IN CLOUD BREAKS. THE
INCREASE IN LOW-LEVEL MOISTURE COMPARED TO PRIOR DAYS WILL SUPPORT
SOMEWHAT GREATER INSTABILITY ACROSS THE LOWER CO RIVER VALLEY
/MLCAPE VALUES OF 1000-1500 J PER KG/...WHILE DEEP-LAYER VERTICAL
SHEAR WILL REMAIN SUFFICIENT FOR ORGANIZED MULTICELL CLUSTERS...AND
MARGINALLY FAVORABLE FOR SUPERCELLS. THE NET RESULT WILL BE AN
ENVIRONMENT SUPPORTING A FEW STORMS CAPABLE OF PRODUCING MARGINALLY
SEVERE HAIL AND ISOLATED DAMAGING GUSTS.

..THOMPSON/HURLBUT.. 09/13/2011

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