DAY1SVR: Day 1 Convective Outlook

ACUS01 KWNS 241623
SWODY1
SPC AC 241622

DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1122 AM CDT WED APR 24 2013

VALID 241630Z - 251200Z

...THERE IS A SLGT RISK OF SVR TSTMS OVER SERN LA...

...THERE IS A SLGT RISK OF SVR TSTMS OVER S-CNTRL NY INTO CNTRL
PA...

...SYNOPSIS...

A BROAD...CYCLONIC FLOW REGIME WILL BE MAINTAINED OVER THE CONUS
THROUGH THE D1 PERIOD. WITHIN THIS LARGE-SCALE PATTERN...A POTENT
SHORT-WAVE TROUGH AND ASSOCIATED 80-90 KT MIDLEVEL JET STREAK OVER
THE MID-MS VALLEY WILL PROGRESS NEWD THROUGH THE UPPER-OH VALLEY AND
INTO SRN/CNTRL QUEBEC BY TONIGHT. IN THE LOW-LEVELS...A COLD FRONT
FROM SWRN ONTARIO AND THE UPPER OH VALLEY SWWD THROUGH THE TN INTO
LOWER-MS VALLEYS WILL ADVANCE EWD THROUGH MUCH OF NEW ENGLAND...TO
OFF THE MID-ATLANTIC COAST...AND INTO THE SERN STATES BY 25/12Z.

...LOWER-MS VALLEY TODAY...

AN MCS WHICH EVOLVED EARLIER THIS MORNING ALONG THE COLD FRONT /AND
AHEAD OF A LOW-LATITUDE VORTICITY MAXIMUM/ OVER THE LOWER-SABINE
VALLEY IS EXPECTED TO PERSIST AT LEAST INTO EARLY AFTERNOON ACROSS
PARTS OF SERN LA. THE INFLUX OF A MOIST...UNSTABLE AIR MASS INTO
THIS SYSTEM WILL CONTINUE TO PROMOTE EMBEDDED BOWING STRUCTURES
CAPABLE OF DAMAGING WINDS AND PERHAPS A BRIEF TORNADO.

EXPECT SEVERE WEATHER POTENTIAL TO DIMINISH WITH EWD EXTENT OVER THE
CNTRL INTO ERN GULF COAST OWING TO A PROGRESSIVELY DRIER BOUNDARY
LAYER.

...NY/PA SWD INTO THE CNTRL APPALACHIANS THIS AFTERNOON AND
EVENING...

LARGE-SCALE FORCING FOR ASCENT WILL INCREASE MARKEDLY TODAY IN
RESPONSE TO THE APPROACH OF THE SHORT-WAVE TROUGH MENTIONED IN THE
SYNOPSIS. AN ASSOCIATED STRENGTHENING OF SURFACE COLD FRONT MOVING
THROUGH THE UPPER OH VALLEY INTO THE NRN/CNTRL APPALACHIANS WILL
PROMOTE THE GRADUAL DEEPENING OF CONVECTIVE ELEMENTS WITH TSTMS
ALREADY DEVELOPING AS OF LATE MORNING OVER SERN OH. THE PRIMARY
UNCERTAINTY REMAINS THE DEGREE TO WHICH THE PRE-FRONTAL AIR MASS CAN
DESTABILIZE GIVEN THE DRY ANTECEDENT BOUNDARY-LAYER CONDITIONS AND
MID AND HIGH-LEVEL CLOUDS OVERSPREADING THE REGION FROM THE WEST.

LATEST CONVECTION-ALLOWING MODEL GUIDANCE REMAINS QUITE CONSISTENT
IN SUGGESTING THE DEVELOPMENT OF A LOW-TOPPED CONVECTIVE BAND ALONG
OR AHEAD OF THE COLD FRONT BY MID/LATE AFTERNOON FROM S-CNTRL NY
INTO CNTRL PA. HERE...STEEPENING LOW-LEVEL LAPSE RATES WILL COMBINE
WITH A RAPIDLY STRENGTHENING DEEP-LAYER WIND FIELD TO INCREASE THE
POTENTIAL FOR EMBEDDED BOWING STRUCTURES CAPABLE OF DAMAGING
WINDS...EVEN DESPITE MLCAPE VALUES OF ONLY A FEW HUNDRED J/KG.
EXPECT THIS SEVERE WEATHER THREAT TO DIMINISH THIS EVENING AS THE
BOUNDARY LAYER COOLS AND STABILIZES.

..MEAD/LEITMAN.. 04/24/2013

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