DAY1SVR: Day 1 Convective Outlook

ACUS01 KWNS 061246
SWODY1
SPC AC 061243

DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0743 AM CDT SUN SEP 06 2009

VALID 061300Z - 071200Z

...NO SVR TSTM AREAS FORECAST...

...SYNOPSIS...
A DEEP MID LEVEL TROUGH OVER THE PAC NW COAST THIS MORNING WILL
PROGRESS EWD OVER THE INTERIOR NW AND NRN ROCKIES THROUGH
TONIGHT...WHILE AN ASSOCIATED COLD FRONT MOVES EWD OVER ID/MT.
STEEP LAPSE RATES AND WEAK INSTABILITY WITH THE MID LEVEL COLD POOL
WILL OVERSPREAD WRN WA TODAY...WHERE A FEW OF THE THUNDERSTORMS NOW
OBSERVED JUST OFFSHORE COULD PERSIST AND SPREAD INLAND. MUCAPE
APPROACHING 500 J/KG IN COMBINATION WITH 500 MB TEMPERATURES OF -22
TO -24 C COULD SUPPORT SMALL HAIL WITH THE STRONGER UPDRAFTS...BUT
THE THREAT FOR LARGE HAIL APPEARS INSUFFICIENT TO WARRANT THE
INTRODUCTION OF LOW SEVERE PROBABILITIES.

A SEPARATE PLUME OF STEEP MID LEVEL LAPSE RATES WILL PRECEDE THE
FRONT OVER MT AND THE WRN DAKOTAS. HOWEVER...LOW-LEVEL MOISTURE
RETURN TO THE NRN HIGH PLAINS WILL BE LIMITED TO BOUNDARY LAYER
DEWPOINTS IN THE LOW-MID 50S BY AFTERNOON AS A RESULT OF VERTICAL
MIXING AND THE INFLUENCE OF A DOWNSTREAM MID LEVEL TROUGH OVER THE
MID MS/LOWER OH VALLEY REGION. THE NET RESULT WILL BE ONLY WEAK
INSTABILITY AND INVERTED-V PROFILES ALONG THE COLD FRONT AND NRN
HIGH PLAINS LEE TROUGH...AND ONLY WEAK VERTICAL SHEAR IN THE WARM
SECTOR WITH THE STRONGER FLOW ALOFT REMAINING W OF THE SURFACE COLD
FRONT.

FARTHER SE ACROSS THE MS/OH VALLEY REGION...THE MID LEVEL TROUGH
WILL ONLY DRIFT EWD IN A WEAK MEAN FLOW REGIME WELL TO THE S OF THE
POLAR JET. WEAK-MODERATE INSTABILITY AND WEAK VERTICAL SHEAR WILL
SUPPORT SCATTERED MULTICELL CLUSTERS...ESPECIALLY ACROSS THE LOWER
OH VALLEY JUST E OF THE MID LEVEL VORTICITY CENTER OVER MO/IL...AND
WITHIN THE DEEP MOISTURE PLUME DOWNSTREAM FROM THE TRAILING TROUGH
AXIS OVER MS/AL. OTHER SCATTERED DIURNAL THUNDERSTORMS CAN BE
EXPECTED ACROSS CENTRAL/S FL IN ASSOCIATION WITH LOCAL SEA BREEZE
CIRCULATIONS AND A WEAK UPPER TROUGH OVER FL AND WRN CUBA.

SCATTERED DIURNAL THUNDERSTORMS ARE ALSO EXPECTED AGAIN TODAY FROM
SRN/ERN AZ NEWD ACROSS NW NM INTO CENTRAL CO AND SE WY. THIS
CORRIDOR WILL BE LOCATED WITHIN THE LOW-MID LEVEL MOISTURE PLUME AND
JUST DOWNSTREAM FROM WEAK MID LEVEL TROUGH.

..THOMPSON/GARNER.. 09/06/2009

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