SPC AC 040559
DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1259 AM CDT MON AUG 04 2008
VALID 051200Z - 061200Z
...THERE IS A SLGT RISK OF SVR TSTMS ACROSS PARTS OF THE GREAT
LAKES/MIDWEST/OH VALLEY...
...SYNOPSIS...
MID-LEVEL TROUGH IS FORECAST TO CONTINUE BUILDING SLOWLY SSEWD OUT
OF CANADA...WITH THE FIRST PIECE OF ENERGY -- IN THE FORM OF A
SHORT-WAVE TROUGH -- FORECAST TO CROSS THE GREAT LAKES REGION THIS
PERIOD. THIS WILL BEGIN TO SUPPRESS THE MID-LEVEL RIDGE SWD ACROSS
THE ERN CONUS...BUT PERMIT A WWD/NWWD STRENGTHENING OF THE RIDGE
ACROSS THE U.S./CANADIAN ROCKIES.
AT THE SURFACE...A COLD FRONT IS FORECAST TO MOVE SEWD ACROSS THE
GREAT LAKES/SSEWD ACROSS THE MIDWEST...IN CONJUNCTION WITH THE
EXPANDING ERN U.S. UPPER TROUGH. THIS FRONT -- AND THE ASSOCIATED
SHORT-WAVE FEATURE MENTIONED PREVIOUSLY -- SHOULD BE THE PRIMARY
FOCUS FOR WIDESPREAD/SEVERE CONVECTION OVER PORTIONS OF THE NERN
QUARTER OF THE CONUS THROUGH THE PERIOD.
...PORTIONS OF THE GREAT LAKES/OH VALLEY/NORTHEAST CONUS...
THUNDERSTORMS ARE FORECAST TO BE ONGOING AT THE START OF THE PERIOD
ACROSS THE MIDWEST/GREAT LAKES/OH VALLEY REGION...THOUGH MODELS
DIFFER WITH RESPECT TO THE LOCATION OF SMALL-SCALE FEATURES ALOFT --
AND THUS THE ASSOCIATED LOCATION OF MORE WIDESPREAD CONVECTIVE
CLUSTERS EARLY IN THE PERIOD. IN ANY CASE...THE EXPECTATION OF
ONGOING CONVECTION COMPLICATES THE FORECAST...AS
CLOUDS/PRECIPITATION SHOULD LIMIT DESTABILIZATION LOCALLY AND
ASSOCIATED CONVECTIVE BOUNDARIES FOCUS AREAS OF GREATER LIKELIHOOD
FOR STORMS.
OVERALL HOWEVER...COLD FRONT ADVANCING ESEWD ACROSS THE GREAT LAKES
AND SSEWD ACROSS THE MIDWEST/OH VALLEY REGION SHOULD FOCUS AFTERNOON
STORM REDEVELOPMENT AS AIRMASS LOCALLY BECOMES MODERATELY UNSTABLE.
WHILE BOTH INSTABILITY AND THE AREAS OF MOST LIKELY CONVECTIVE
REDEVELOPMENT REMAIN DIFFICULT TO FORECAST ATTM...SHEAR IS EXPECTED
TO BE QUITE FAVORABLE FOR SEVERE STORMS. FLOW IS FORECAST TO BE
ROUGHLY UNIDIRECTIONAL/WNWLY WITH HEIGHT ABOVE THE
SURFACE...INCREASING FROM 20 TO 30 KT AT LOW LEVELS TO ROUGHLY 40 TO
50 KT AT MID LEVELS. MAIN SEVERE THREAT IS FORECAST TO BE DAMAGING
WINDS...WITH THE THREAT POSSIBLY BECOMING FAIRLY WIDESPREAD THROUGH
THE AFTERNOON AND EVENING AS STORMS MERGE INTO MULTIPLE SMALL-SCALE
LINES/BOWS. THREAT SHOULD LAST WELL INTO THE OVERNIGHT HOURS...AS
STORMS SPREAD EWD ACROSS PA/NY AND TOWARD THE MID-ATLANTIC
COAST...AND SEWD ACROSS THE OH VALLEY REGION.
...CENTRAL/NRN HIGH PLAINS REGION...
ELY/SELY UPSLOPE FLOW IN POST-FRONTAL REGIME SHOULD RESULT IN THE
DEVELOPMENT OF ISOLATED TO SCATTERED STORMS BY LATE AFTERNOON...AS
AIRMASS BECOMES AT LEAST MARGINALLY UNSTABLE. WITH LOW-LEVEL
ELY/SELY FLOW BENEATH MODERATE WNWLYS AT MID LEVELS...SHEAR WILL
SUPPORT BOTH ORGANIZED/SEVERE STORMS...AND THE LIKELIHOOD FOR SEWD
MOVEMENT OF CONVECTION OFF THE HIGHER TERRAIN THROUGH THE EVENING.
WHILE DEGREE OF THREAT WILL LIKELY BE DEPENDENT UPON THE DEGREE OF
DESTABILIZATION WHICH CAN OCCUR IN AN OTHERWISE POST-FRONTAL
AIRMASS...THREAT APPEARS SUFFICIENT TO INTRODUCE LOW /5%/ SEVERE
PROBABILITY THIS FORECAST.
...WRN GULF COAST...
TROPICAL SYSTEM EDOUARD IS FORECAST TO MAKE LANDFALL NEAR GALVESTON
BAY EARLY IN THE PERIOD...PER LATEST FORECASTS FROM THE NHC.
ENHANCED LOW-LEVEL SHEAR ALONG THE N SIDE OF EDOUARDS TRACK MAY BE
SUFFICIENT FOR AN ENHANCED THREAT FOR BRIEF TORNADOES -- AND THUS
WILL INCLUDE A SMALL/LOW-PROBABILITY THREAT AREA TO REFLECT THIS
THREAT.
..GOSS.. 08/04/2008
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NOTE: THE NEXT DAY 2 OUTLOOK IS SCHEDULED BY 1730Z
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