DAY1SVR: Day 1 Convective Outlook

ACUS01 KWNS 041248
SWODY1
SPC AC 041246

DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0746 AM CDT TUE SEP 04 2012

VALID 041300Z - 051200Z

...THERE IS A SLGT RISK OF SVR TSTMS ACROSS PARTS OF THE CNTRL
PLAINS...UPPER MS VALLEY AND WRN GREAT LAKES...

...THERE IS A SLGT RISK OF SVR TSTMS OVER PORTIONS OF NERN OH AND
WRN PA/NY...

...THERE IS A SLGT RISK OF SVR TSTMS ACROSS PORTIONS OF THE NCNTRL
GULF COAST...

...SYNOPSIS...
BROADLY CYCLONIC MID LEVEL FLOW WILL STRENGTHEN FROM THE NRN PLAINS
TO GREAT LAKES AS THE NEXT IN A SERIES OF SHORTWAVE TROUGHS ROTATES
THROUGH THE BASE OF A LARGE UPPER LOW OVER CNTRL CANADA. THIS NEXT
MID/UPPER WAVE WILL MOVE TOWARD THE DAKOTAS AND WRN MN THROUGH
TONIGHT WITH A SHARPENING COLD FRONT SPREADING ACROSS THESE AREAS
THROUGH WEDNESDAY MORNING. MEANWHILE...A LEADING LOWER AMPLITUDE
IMPULSE...CURRENTLY MOVING EAST FROM SRN ONTARIO AND LOWER MI...WILL
PRODUCE WEAK HEIGHT FALLS ACROSS THE ERN GREAT LAKES AND NEW
ENGLAND. TO THE SOUTH OF THESE BETTER DEFINED DISTURBANCES...THE
SUBTROPICAL RIDGE WILL BE SOMEWHAT SUPPRESSED OVER THE CNTRL/SRN
PLAINS...THE INCREASINGLY FRAGMENTED REMNANT CIRCULATION FROM ISAAC
WILL MOVE SOUTH ACROSS THE NCNTRL GULF COAST...AND A WEAK UPPER LOW
OFF THE EAST COAST OF FL WILL REMAIN NEARLY STATIONARY.

SFC FEATURES IN MOST AREAS ARE ILL-DEFINED AND SUBTLE. A BROAD WARM
FRONTAL ZONE EXISTS OVER THE MID ATLANTIC REGION NWD TO NY AHEAD OF
THE SFC TROUGH AXIS SUPPORTING ONGOING TSTMS FROM LOWER MI INTO
ONTARIO. THIS SFC TROUGH EXTENDS W-SWWD TO MO/KS WHERE IT ALSO
APPEARS TO BE SUPPORTING SCATTERED MORNING CONVECTION. A DECAYING
MCS ACROSS AL HAS GENERATED A STABLE COLD POOL WITH AN OUTFLOW
BOUNDARY NEAR THE MS BORDER. AND...A WEAK BUT COHERENT SFC LOW WAS
LOCATED ALONG A SUBTLE SFC TROUGH OVER MN. THESE ARE THE PRIMARY
FEATURES THAT SHOULD DRIVE AN INCREASE IN CONVECTIVE POTENTIAL
THROUGH THE DAY TODAY.

...MN/WI/IA...
STRONG DESTABILIZATION IS FORECAST TO OCCUR NEAR THE WEAK SFC LOW
AND PRE-FRONTAL TROUGH AXIS FROM SERN MN INTO WRN WI BY AFTERNOON.
CAPPING/INHIBITION IN THE AREA HAS DIMINISHED IN RECENT DAYS AS MID
LEVEL TEMPERATURES HAVE COOLED. MEANWHILE...LOW LEVEL MOISTURE AND
STEEPENING LAPSE RATES WILL CONTRIBUTE TO MLCAPE OF 2000-3000 J/KG
BY AFTERNOON. STORMS FORMING NEAR THE LOW AND TROUGH WILL EXIST
AMIDST SUFFICIENT SHEAR FOR PERSISTENCE AND ORGANIZATION WITH
SUPERCELLS AND/OR EVOLVING LINE SEGMENTS POSSIBLE. MAGNITUDE OF
INSTABILITY AND SHEAR ANTICIPATED COULD RESULT IN A COUPLE OF STORMS
CAPABLE OF PRODUCING VERY LARGE HAIL. WIND DAMAGE POTENTIAL MAY
INCREASE IF CONVECTION CAN GROW AND ORGANIZE INTO A SMALL FORWARD
PROPAGATING MCS INTO THE EVENING. ADDITIONAL STRONG TO SEVERE STORMS
ARE POSSIBLE OVERNIGHT AS THE COLD FRONT SURGES EAST FROM THE
DAKOTAS INTO MN. DEGREE OF AVAILABLE INSTABILITY AHEAD OF THE FRONT
WILL BE MODULATED BY PRIOR CONVECTIVE DEVELOPMENT AND COVERAGE.
GIVEN UNCERTAINTIES AND TIMING OF THE FRONTAL ADVANCE...PORTIONS OF
THE ERN DAKOTAS AND WRN MN WILL REMAIN IN LOWER SEVERE PROBABILITIES
FOR NOW.

A SEPARATE AREA OF SEVERE STORM DEVELOPMENT POTENTIAL IS INDICATED
IN LATEST GUIDANCE ALONG THE TROUGH/THERMAL AXIS FROM ERN NEB INTO
IA. CAPPING WILL BE MORE SUBSTANTIAL IN THESE AREAS BUT PERSISTENT
WARM ADVECTION AND BOUNDARY LAYER HEATING MAY PROVE ADEQUATE FOR
STORM INITIATION LATE IN THE AFTERNOON OR BY EARLY EVENING. THIS
DEVELOPMENT WILL OCCUR COINCIDENT WITH AN INCREASE IN WLY MID LEVEL
FLOW SUFFICIENT FOR STORM ORGANIZATION WITH SOME CHANCE FOR BOTH
LARGE HAIL AND LOCALLY DAMAGING WINDS.

...OH/PA/NY...
HAVE ADDED A SLGT RISK TO THESE AREAS GIVEN CURRENT CONVECTIVE
TRENDS FROM LOWER MI TO THE ERN GREAT LAKES. LOW LEVEL MOISTURE HAS
INCREASED AHEAD OF THE ADVANCING TROUGH THAT IS DRIVING CURRENT
STORMS WITH DEWPOINTS NOW NEARING 70F FROM NERN OH TO WRN NY.
SATELLITE IMAGERY DOES DEPICT AN INCREASE IN LOW CLOUDS THIS MORNING
BUT AT LEAST SOME DIURNAL DESTABILIZATION APPEARS LIKELY WITH MLCAPE
REACHING 1000 J/KG IN SOME AREAS...PERHAPS LOCALLY HIGHER WHERE
GREATER INSOLATION OCCURS. AS LIFT ASSOCIATED WITH THE SFC AND UPPER
TROUGHS SPREADS EAST THROUGH THE DAY STORMS ARE EXPECTED TO INCREASE
IN COVERAGE ACROSS THE SLGT RISK AREA. EFFECTIVE BULK SHEAR ALSO
STRENGTHENS TO AROUND 30KT AND EXPECT NUMEROUS MARGINALLY ORGANIZED
MULTICELL STORMS POSING A THREAT OF DOWNBURST WINDS.

...NCNTRL GULF COAST...
LATENT HEAT RELEASE FROM REPEAT DEEP CONVECTION APPEARS TO HAVE
ENHANCED MID LEVEL CIRCULATION ACROSS SRN AL THIS MORNING WITH
POSSIBLE MCV EVOLVING COINCIDENT WITH THE REMNANT CIRCULATION FROM
ISAAC. STORM-SCALE AND NAM GUIDANCE ARE IN REASONABLE AGREEMENT AND
INDICATE THAT AREAS ON THE WRN FLANK OF THE ONGOING
CONVECTION...FROM MS/AL BORDER WWD ACROSS MS TO ERN LA...WILL BECOME
STRONGLY UNSTABLE WITH HEATING OF THE DAY. THIS SEEMS REASONABLE
BASED ON LATEST SATELLITE IMAGERY DEPICTING ONLY THIN SCATTERED
CLOUDS ACROSS THESE AREAS WHERE SFC DEWPOINTS ARE IN THE MID 70S F.
WIND PROFILES ACROSS THE REGION REMAIN CHARACTERIZED BY WEAK LOW
LEVEL W-SWLYS TOPPED BY MODEST NLY FLOW IN THE MID LEVELS. THE
VEERED WIND PROFILES SHOULD CONTRIBUTE TO STORM ORGANIZATION AND
POSSIBLY SOME UPSCALE GROWTH WITH SWD/SWWD CELL PROPAGATION AND AN
INCREASE IN DAMAGING WIND HAZARD INTO THIS AFTERNOON.

..CARBIN/ROGERS.. 09/04/2012

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