DAY1SVR: Day 1 Convective Outlook

ACUS01 KWNS 281250
SWODY1
SPC AC 281248

DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0748 AM CDT TUE AUG 28 2012

VALID 281300Z - 291200Z

...THERE IS A SLGT RISK OF SVR TSTMS THROUGH TONIGHT ACROSS PARTS OF
THE NRN GULF COAST...

...NRN GULF COAST THROUGH TONIGHT...
TROPICAL STORM ISAAC CONTINUES TO MOVE NWWD TOWARD THE SE LA COAST.
THERE HAS BEEN A GRADUAL WWD SHIFT IN THE NHC FORECAST TRACK...AND A
CONTINUED WWD TREND SEEMS REASONABLE AS THE MIDLEVEL RIDGE OVER THE
PLAINS DEVELOPS EWD TOWARD THE MS VALLEY DURING THE NEXT COUPLE OF
DAYS. ISAAC HAS YET TO REACH HURRICANE STATUS...AS SATELLITE
IMAGERY AND REGIONAL SOUNDINGS SHOW AN IMPEDED OUTFLOW PATTERN ALOFT
TO THE N-NE-E OF THE CYCLONE CORE. THERE IS ALSO A CHANNEL OF DRY
AIR IN THE LOWER TROPOSPHERE FEEDING INTO THE NW QUADRANT OF THE
CYCLONE PER LIX/JAN SOUNDINGS AND SURFACE OBSERVATIONS SINCE 28/00Z.
THE NET RESULT OF THESE PROCESSES HAS BEEN TO LIMIT THE
ORGANIZATION/INTENSITY OF THE STORM CORE...WHICH HAS LIKEWISE
DISRUPTED CONVECTIVE COVERAGE AND THE MAGNITUDE OF LOW-LEVEL SHEAR
IN THE NORMALLY-FAVORED NE QUADRANT.

STILL...THE ENVIRONMENT IS NOT OVERLY HOSTILE TO TROPICAL
CYCLOGENESIS...AND SOME STRENGTHENING OF ISAAC IS FORECAST PRIOR TO
LANDFALL /SEE LATEST NHC ADVISORIES FOR DETAILS/. CONTINUED NWWD
MOTION AND BROADENING OF THE STRONGER WIND FIELD WILL BRING THE
TROPICAL AIR MASS INLAND ACROSS THE N CENTRAL AND NE GULF
COAST...WHERE LOW-LEVEL SHEAR WILL BE SUFFICIENT FOR SUPERCELLS IN
THE BROKEN OUTER BANDS. CLOUD BREAKS WILL ALSO ALLOW POCKETS OF
SURFACE HEATING WHICH WILL LOCALLY BOOST INSTABILITY /REFER TO MD
1826 FOR ADDITIONAL SHORT-TERM INFORMATION/. THUS...WILL MAINTAIN
THE SLIGHT RISK AND TORNADO PROBABILITIES IN THIS UPDATE...THOUGH
WILL SHRINK THE PERIPHERAL EXTENT OF THE THREAT AREA PER RELATIVELY
SLOW MOVEMENT OF THE STORM AND SOMEWHAT LIMITED INLAND INTRUSION OF
THE RICHEST LOW-LEVEL MOISTURE/BUOYANCY.

...ERN DAKOTAS TO UPPER MS VALLEY THROUGH TONIGHT...
A CLUSTER OF ELEVATED THUNDERSTORMS OVER ERN SD/WRN MN THIS
MORNING...IN ADVANCE OF A DIFFUSE SHORTWAVE TROUGH CRESTING THE NRN
HIGH PLAINS RIDGE...WILL SPREAD SEWD OVER MN AND LIKELY DISSIPATE BY
ABOUT MIDDAY AS A SWLY LLJ AND ASSOCIATED WAA WEAKEN. S OF THIS
CONVECTION...A PLUME OF STEEP LAPSE RATES WILL SPREAD EWD FROM SD TO
SRN MN. LOW-LEVEL MOISTURE IS RATHER MODEST IN THE WARM SECTOR WITH
BOUNDARY LAYER DEWPOINTS IN THE LOWER 60S...AND STRONG SURFACE
HEATING THIS AFTERNOON WILL LIKELY RESULT IN SUFFICIENT VERTICAL
MIXING TO REDUCE SURFACE DEWPOINTS TO THE UPPER 50S. FORECAST
SOUNDINGS CONTINUE TO SUGGEST THAT THE WARMING ABOVE THE SURFACE
WILL HELP MAINTAIN A CAP THROUGH THE AFTERNOON...AND SURFACE-BASED
THUNDERSTORM DEVELOPMENT IS QUESTIONABLE THIS AFTERNOON. IF STORMS
DO FORM...THE STORM ENVIRONMENT WILL SUPPORT SUPERCELLS WITH A RISK
FOR ISOLATED LARGE HAIL/DAMAGING GUSTS. OTHERWISE...MORE ELEVATED
CONVECTION COULD FORM LATER TONIGHT OVER SE MN/WRN WI/NE IA AS THE
LLJ/WAA STRENGTHEN.

...SE NEW ENGLAND THIS MORNING...
A MIDLEVEL SHORTWAVE TROUGH AND ASSOCIATED COLD FRONT WILL MOVE
ACROSS NEW ENGLAND TODAY. THE FRONT IS PRECEDED BY A BAND OF RAIN
WITH EMBEDDED CONVECTION. LAPSE RATES AND BUOYANCY ARE EXPECTED TO
REMAIN WEAK ACROSS THE AREA...BUT VERTICAL SHEAR WILL BE SUFFICIENT
FOR A MARGINAL DAMAGING WIND RISK WITH THE STRONGER EMBEDDED
CONVECTION...IN THE AREA OF LOWER 70S SURFACE DEWPOINTS.

..THOMPSON/COHEN.. 08/28/2012

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