SWODY1
SPC AC 201251
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0751 AM CDT SAT SEP 20 2008
VALID 201300Z - 211200Z
...NO SVR TSTM AREAS FORECAST...
...NRN GREAT BASIN AND ROCKIES AREA TODAY...
A PRONOUNCED MID LEVEL SHORTWAVE TROUGH WILL PROGRESS EWD FROM NRN
NV/ERN ORE/SW ID TO NW CO/WY AND MT BY EARLY SUNDAY. ASCENT
DOWNSTREAM FROM THE TROUGH WILL RESULT IN SUFFICIENT LOW-MID LEVEL
MOISTENING FOR AT LEAST WEAK BUOYANCY...GIVEN MID LEVEL LAPSE RATES
OF 7-8 C/KM. EXPECT THUNDERSTORM COVERAGE TO INCREASE DURING THE
AFTERNOON FROM NE UT INTO WRN WY/ERN ID AND SW MT WHERE THE LARGE
SCALE ASCENT COINCIDES WITH DAYTIME HEATING OVER THE HIGH TERRAIN.
THOUGH INSTABILITY WILL BE RATHER LIMITED...INVERTED-V STRUCTURES IN
THE LOW LEVELS AND MODERATE MID LEVEL FLOW COULD RESULT IN ISOLATED
STRONG OUTFLOW GUSTS...AND MARGINALLY SEVERE HAIL COULD OCCUR GIVEN
RELATIVELY COOL MID LEVEL TEMPERATURES WITH THE STEEP LAPSE RATES.
...MS VALLEY TODAY...
WIDELY-SCATTERED TO SCATTERED THUNDERSTORMS ARE AGAIN EXPECTED TODAY
INTO THIS EVENING FROM MO/IL SWD TO MS/LA IN ASSOCIATION WITH A
BROAD/WEAK MID LEVEL TROUGH AND SEVERAL EMBEDDED SMALLER SCALE
WAVES. REGIONAL 12Z SOUNDINGS...MODIFIED FOR DAYTIME
HEATING...REVEAL THE POTENTIAL FOR MLCAPE OF 500-1000 J/KG WITH
LITTLE CONVECTIVE INHIBITION. HOWEVER...VERTICAL SHEAR WILL BE WEAK
OVER THE MS VALLEY...THUS LIMITING ANY POTENTIAL FOR ORGANIZED
SEVERE STORMS.
...UPPER MS VALLEY TO LOWER MI THIS AFTERNOON...
A SURFACE COLD FRONT WILL MOVE SEWD ACROSS WI/MI IN THE WAKE OF A
STRONG NRN STREAM SHORTWAVE TROUGH NOW CROSSING CENTRAL ONTARIO AND
WRN QUEBEC. HOWEVER...LARGE SCALE ASCENT WITH THIS TROUGH WILL
REMAIN LARGELY IN CANADA...LEAVING ONLY SHALLOW/WEAK ASCENT ALONG
THE FRONT IN WI/MI. MODIFIED 12Z SOUNDINGS SHOW THE POTENTIAL FOR
AFTERNOON MLCAPE OF 1000 J/KG OR GREATER WITH AFTERNOON TEMPERATURES
IN THE 80S AND BOUNDARY LAYER DEWPOINTS IN THE MID-UPPER 50S.
STILL...SOME CONVECTIVE INHIBITION MAY REMAIN THROUGH THE AFTERNOON
AND LIFT ALONG THE FRONT WILL BE WEAK...SO THUNDERSTORM COVERAGE IS
EXPECTED TO BE RATHER SPARSE. STEEP MID LEVEL LAPSE/MODERATE
INSTABILITY WOULD APPEAR SUPPORTIVE OF SOME HAIL THREAT...THOUGH
WEAK VERTICAL SHEAR AND ONLY ISOLATED STORM COVERAGE WILL LIMIT ANY
SEVERE THREAT.
..THOMPSON/SMITH.. 09/20/2008
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