DAY1SVR: Day 1 Convective Outlook

ACUS01 KWNS 291254
SWODY1
SPC AC 291252

DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0752 AM CDT WED AUG 29 2012

VALID 291300Z - 301200Z

...THERE IS A SLGT RISK OF SVR TSTMS ACROSS PARTS OF THE LOWER MS
VALLEY THROUGH TONIGHT...

...LOWER MS VALLEY THROUGH TONIGHT...
HURRICANE ISAAC IS DRIFTING WWD OVER SE LA...AND THIS GENERAL MOTION
IS EXPECTED TO PERSIST TODAY. THE OFFICIAL FORECAST FROM NHC
PROJECTS A PATH INTO S CENTRAL LA BY THE END OF THIS FORECAST
PERIOD...THOUGH SOME UNCERTAINTY EXISTS REGARDING THE LONGER-TERM
PATH OF ISAAC AND THE INFLUENCE OF THE MIDLEVEL RIDGE DEVELOPING EWD
FROM THE CENTRAL PLAINS TO THE MS VALLEY. ASSUMING ISAAC MOVES
FARTHER INLAND...GRADUAL WEAKENING IS EXPECTED.

THE CONVECTIVE STRUCTURE OF ISAAC HAS BECOME MORE PROTOTYPICAL OF A
LANDFALLING HURRICANE...WITH ASYMMETRY IN THE CONVECTION FAVORING
THE ERN SEMI-CIRCLE OF THE STORM. CONVECTION IS ALSO MORE CLEARLY
PHASED WITH THE REGION OF STRONGER VERTICAL SHEAR TO THE NE OF THE
CYCLONE CENTER...WHERE PERSISTENT BANDS WITH EMBEDDED ROTATING
STORMS HAVE BEEN OBSERVED FROM THE MS SOUND NWWD INTO SE MS. THIS
BASIC SCENARIO WILL CONTINUE INTO THE DAY...WHEN OCCASIONAL CLOUD
BREAKS WILL CONTRIBUTE TO POCKETS OF STRONGER SURFACE HEATING/
BUOYANCY. AS SUCH...THE PATTERN SUPPORTS THE RISK FOR A FEW
TORNADOES ACROSS EXTREME SW AL AND SRN MS THIS MORNING...WITH A
GRADUAL WWD AND INLAND SPREAD OF THE TORNADO THREAT ACROSS LA/MS
TODAY IN CONJUNCTION WITH WWD MOVEMENT OF THE CYCLONE.

...CENTRAL ND LATE THIS AFTERNOON...
A MIDLEVEL SHORTWAVE TROUGH OVER THE NRN ROCKIES THIS MORNING WILL
EJECT ENEWD OVER MT AND THE SRN PRAIRIE PROVINCES BY EARLY
TONIGHT...AS AN ASSOCIATED SURFACE COLD FRONT CROSSES MT AND THE
DAKOTAS. REGIONAL 12Z SOUNDINGS SHOW A WARM EML AND SOMEWHAT
LIMITED LOW-LEVEL MOISTURE IN ADVANCE OF THIS SYSTEM...WITH SURFACE
TEMPERATURES AOA 100 F NEEDED TO MIX THROUGH THE BASE OF THE EML
NEAR 850 MB. THERE WILL BE A SMALL WINDOW OF OPPORTUNITY FOR
HIGH-BASED THUNDERSTORMS ALONG THE FRONT LATE THIS AFTERNOON/EVENING
ACROSS CENTRAL ND...WITH A CONDITIONAL RISK FOR ISOLATED
STRONG/DAMAGING OUTFLOW GUSTS.

...SE GA/SC THIS AFTERNOON...
THE NERN EXTENT OF THE MOISTURE PLUME ASSOCIATED WITH ISAAC AND
DAYTIME HEATING S OF THE THICKER CLOUDS AND A WEAK SURFACE FRONT IN
THE CAROLINAS WILL CONTRIBUTE TO AFTERNOON MLCAPE VALUES OF
1500-2000 J/KG. DCAPE OF 600-1000 J/KG AND MODERATE BUOYANCY COULD
RESULT IN SUFFICIENTLY STRONG PRECIPITATION LOADING AND DOWNDRAFTS
FOR A MARGINAL DAMAGING WIND RISK WITH THE STRONGEST MULTICELL
CLUSTERS.

..THOMPSON/COHEN.. 08/29/2012

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