SWODY1
SPC AC 260559
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1259 AM CDT SAT SEP 26 2009
VALID 261200Z - 271200Z
...THERE IS A SLGT RISK OF SVR TSTMS FROM SERN MO...SRN IL...SWRN
IND AND EXTREME WRN KY...
...SYNOPSIS...
UPPER LOW OVER THE CNTRL U.S. IS IN THE PROCESS OF TRANSITIONING TO
AN OPEN WAVE AND WILL EJECT THROUGH THE OH AND TN VALLEYS IN
RESPONSE TO A STRONG UPSTREAM IMPULSE MOVING INTO SWRN CANADA. AT
THE SURFACE A FRONTAL BOUNDARY FROM THE LOWER MS VALLEY THROUGH THE
TN AND OH VALLEYS WILL SHIFT EWD. WEDGE FRONT WILL REMAIN IN PLACE
ACROSS THE CAROLINAS. A WARM FRONT IS FORECAST TO LIFT NWD ALONG THE
NC COASTAL AREA.
...MID MS THROUGH OH VALLEY...
RICHER BOUNDARY LAYER MOISTURE REMAINS CONFINED TO THE SERN U.S. AS
OF LATE FRIDAY EVENING. WITH ONLY WEAK LOW LEVEL RESPONSE TO FORCING
ATTENDING THE UPPER TROUGH...MOISTURE ADVECTION IN THIS REGION WILL
LIKELY REMAIN LIMITED. WITH THE EXCEPTION OF SOME 60S DEWPOINTS IN
WRN KY...BOUNDARY LAYER DEWPOINTS IN THE LOW TO MID 50S WILL LIKELY
CHARACTERIZE THE BOUNDARY LAYER OVER MUCH OF THIS REGION. THE COLDER
AIR ALOFT NORTH OF UPPER JET AXIS ATTENDING THE UPPER TROUGH WILL
LIKELY REMAIN NORTH OF THE RICHER LOW LEVEL MOISTURE. BUT...THE
COMBINATION OF DIABATIC WARMING...STEEP MID LEVEL LAPSE RATES AND
DEWPOINTS IN THE 50S WILL RESULT IN MLCAPE FROM 400 TO 800 J/KG. AS
THE ATMOSPHERE DESTABILIZES...STORMS WILL LIKELY REDEVELOP FROM
PARTS OF MO INTO SRN IL IN ASSOCIATION WITH VORT MAX ROTATING
THROUGH BASE OF UPPER TROUGH. ACTIVITY WILL SUBSEQUENTLY SPREAD EWD
THROUGH WRN KY AND PARTS OF SRN IND WHERE IT WILL LIKELY ENCOUNTER
SOMEWHAT GREATER LOW LEVEL MOISTURE. VERTICAL SHEAR OF 40 TO 50 KT
AND STEEP LAPSE RATES WILL PROMOTE UPDRAFT ROTATION AND A THREAT FOR
ISOLATED LARGE HAIL. ISOLATED STRONG WIND GUSTS MAY ALSO ACCOMPANY
SOME STORMS.
...NC COASTAL AREA...
WITH PRIMARY FORCING ASSOCIATED WITH EJECTING IMPULSE REMAINING WELL
TO THE WEST OF OFFSHORE BOUNDARY...ONLY WEAK CYCLOGENESIS IS
FORECAST NEAR THE NC COAST. THIS IN ADDITION TO COLD AIR DAMMING
REINFORCED BY ONGOING AREAS OF PRECIPITATION SUGGEST THE COASTAL
BOUNDARY WILL NOT ADVANCE FARTHER INLAND THAN THE NC COASTAL AREAS.
A CONDITIONAL THREAT WILL EXIST FOR ISOLATED STRONG WIND GUSTS OR A
BRIEF TORNADO IN VICINITY OF THE BOUNDARY GIVEN FAVORABLE LOW LEVEL
HODOGRAPHS. HOWEVER...WEAK LAPSE RATES AND INSTABILITY SUGGEST ONLY
LOW PROBABILITIES ARE WARRANTED AT THIS TIME.
...SERN STATES...
THUNDERSTORMS WILL CONTINUE DEVELOPING WITHIN PLUME OF DEEP
SUBTROPICAL MOISTURE OVER THE SERN STATES. STRONGER FLOW ALOFT WILL
GRADUALLY SPREAD EWD AND BEGIN TO OVERTAKE THE WARM SECTOR AS THE
UPPER TROUGH ADVANCES EWD. HOWEVER...IT APPEARS THE STRONGER UPPER
WIND PROFILES WILL REMAIN WEST OF THE SUBTROPICAL MOISTURE PLUME
WHERE SUBSIDENCE COULD POTENTIALLY LIMIT THUNDERSTORM DEVELOPMENT.
THIS ALONG WITH WEAK LAPSE RATES AND WEAK LOW LEVEL FLOW SUGGEST ANY
SEVERE THREAT IN THIS REGION SHOULD REMAIN LIMITED.
..DIAL/SMITH.. 09/26/2009
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