SPC AC 261726
DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1226 PM CDT SAT SEP 26 2009
VALID 271200Z - 281200Z
...THERE IS A SLGT RISK OF SVR TSTMS ACROSS THE GREAT LAKES
REGION...
...SYNOPSIS...
AN INCREASINGLY PROGRESSIVE LARGE SCALE REGIME WILL CONTINUE TO
EVOLVE INTO SUNDAY. EARLIER STAGNANT/CLOSED LOW OVER THE CENTRAL
STATES WILL CONTINUE TO OPEN/ACCELERATE ENE ACROSS THE CENTRAL
APPALACHIANS/MID ATLANTIC STATES TO THE WESTERN ATLANTIC ON
SUNDAY...AHEAD OF A DIGGING/CONSIDERABLY AMPLIFYING UPPER TROUGH
OVER ONTARIO AND THE UPPER MIDWEST/UPPER GREAT LAKES. ASSOCIATED
COLD FRONT IS EXPECTED TO RACE EAST-SOUTHEASTWARD DURING THE
AFTERNOON/NIGHT ACROSS MUCH OF THE MIDDLE/UPPER MS RIVER VALLEY AND
GREAT LAKES REGION/OH VALLEY.
...GREAT LAKES REGION/OHIO VALLEY...
PRIMARY IMPETUS FOR SEVERE TSTM POTENTIAL SUNDAY AFTERNOON/EVENING
WILL BE THE CONSIDERABLY AMPLIFYING UPPER TROUGH OVER THE UPPER
MIDWEST AND ASSOCIATED FAST MOVING COLD FRONT ACROSS THE GREAT LAKES
REGION/OH RIVER VALLEY. AHEAD OF THE PARENT TROUGH/COLD FRONT...A
STRENGTHENING LOW LEVEL WIND FIELD WILL HELP TO QUICKLY TRANSPORT A
SLIGHTLY HIGHER MOISTURE CONTENT AIRMASS NNE-WARD ACROSS THE
MIDWEST/GREAT LAKES REGION DURING THE DAY WITHIN A RELATIVELY NARROW
CORRIDOR AHEAD OF THE COLD FRONT. MOISTURE WILL REMAIN RATHER MODEST
NONETHELESS...WITH 50S F PRE-COLD FRONTAL SURFACE DEWPOINTS ACROSS
MUCH OF THE REGION...WITH THE POSSIBILITY OF SOME LOWER 60S F
SURFACE DEWPOINTS ACROSS THE MIDDLE MS RIVER VALLEY. EVEN WITH
LIMITED HEATING AND SURFACE BASED BUOYANCY /500-750 J PER KG MLCAPE/
DURING THE AFTERNOON...MARKEDLY STRENGTHENING DEEP LAYER WIND FIELDS
AND RATHER STRONG HEIGHT FALLS /100-180 METERS BY SUNDAY
NIGHT/...ALONG WITH STEEPENING MID LEVEL LAPSE RATES AND THE FAST
MOVING NATURE OF THE COLD FRONT...SHOULD RESULT IN AN INCREASINGLY
ORGANIZED/LOW TOPPED CONVECTIVE LINE BY LATE AFTERNOON/EARLY EVENING
ACROSS PORTIONS OF MI/WI AS WELL AS IL/INDIANA.
DAMAGING WINDS WILL LIKELY BE THE PRIMARY HAZARD...WITH SOME
POSSIBILITY FOR HAIL AS WELL /MAINLY WITHIN THE FIRST FEW HOURS OF
CONVECTIVE INITIATION/. IN ADDITION...AN ISOLATED TORNADO RISK
CANNOT BE RULED OUT UNTIL AROUND SUNSET...PERHAPS MOST PROBABLE
ACROSS PORTIONS OF SOUTHERN/EASTERN WI AND/OR WESTERN LOWER MI/FAR
NORTHERN IL GIVEN ANTICIPATED ELONGATED/MODESTLY CURVED LOW LEVEL
HODOGRAPHS IMMEDIATELY AHEAD OF THE COLD FRONT. EVEN WITH SCANT NEAR
SURFACE BUOYANCY AND INCREASING CINH AFTER SUNSET...THE POTENTIAL
FOR A RELATIVELY WELL-ORGANIZED/LOW-TOPPED CONVECTIVE LINE AND
TURBULENT MIXING COULD LEAD TO A CONTINUED DAMAGING WIND RISK /AT
LEAST ON AN ISOLATED BASIS/ THROUGH THE EVENING/PERHAPS EVEN
OVERNIGHT ACROSS LOWER MI AND PORTIONS OF THE OH VALLEY.
...SOUTHERN NEW ENGLAND...
QUESTIONS REMAIN REGARDING THE EXPECTED TRACK OF A NEAR COASTAL
SURFACE LOW AND STABILITY OF THE INLAND AIRMASS ACROSS SOUTHERN NEW
ENGLAND ON SUNDAY. IN SPITE OF POOR LAPSE RATES AND QUESTIONABLE
NEAR SURFACE BUOYANCY...THE DEEPENING NATURE OF THE SURFACE LOW FROM
THE MID ATLANTIC COAST TO THE LONG ISLAND/SOUTHERN NEW ENGLAND
COAST...ALONG WITH STRENGTHENING WIND FIELDS...APPEAR TO WARRANT
CONDITIONAL/MARGINAL SEVERE PROBABILITIES SUNDAY AFTERNOON/EVENING.
..GUYER.. 09/26/2009
CLICK TO GET WUUS02 PTSDY2 PRODUCT
NOTE: THE NEXT DAY 2 OUTLOOK IS SCHEDULED BY 0600Z
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