SWODY1
SPC AC 180048
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0748 PM CDT WED SEP 17 2008
VALID 180100Z - 181200Z
...NO SVR TSTM AREAS FORECAST...
...WESTERN STATES...
ONE CONCENTRATION OF SCATTERED THUNDERSTORM ACTIVITY CONTINUES TO BE
FOCUSED ACROSS PARTS OF THE EASTERN GREAT BASIN INTO THE WESTERN
COLORADO ROCKIES. FROM THE BULK OF MODEL GUIDANCE...THIS GENERALLY
APPEARS TO BE SUPPORTED BY FORCING ASSOCIATED WITH AN AREA OF
ENHANCED UPPER DIVERGENCE ACCOMPANYING A WEAK UPPER TROUGH SHIFTING
EAST SOUTHEASTWARD ACROSS THE CENTRAL/SOUTHERN ROCKIES TOWARD THE
SOUTHERN PLAINS. MUCH OF THE ONGOING STORM ACTIVITY WILL PROBABLY
BEGIN TO WEAKEN WITH THE ONSET OF MORE RAPID SURFACE COOLING BY
02-03Z...WITH ANY LINGERING ACTIVITY DIMINISHING NOT LONG
THEREAFTER...AS FAVORABLE LARGE-SCALE FORCING WEAKENS/PROGRESSES OFF
TO THE SOUTHEAST.
AFOREMENTIONED IMPULSE MAY HAVE ALSO AIDED EARLIER CONCENTRATION OF
THUNDERSTORM ACTIVITY ACROSS THE SOUTHERN CALIFORNIA DESERTS AND
PARTS OF THE LOWER COLORADO VALLEY...WHERE MOISTURE LEVELS REMAIN
FAIRLY HIGH AND MODERATE TO STRONG DESTABILIZATION OCCURRED.
HOWEVER...STORMS HAVE ALREADY BECOME FEWER IN NUMBER...LIKELY DUE TO
AN INCREASE IN SUBSIDENCE ALOFT. AND...REMAINING STORMS ARE
EXPECTED TO DIMINISH BY 02-03Z...WITH THE ONSET OF MORE RAPID
BOUNDARY LAYER COOLING.
FARTHER NORTH...A WEAK MOISTURE RETURN FROM THE LOWER COLORADO
VALLEY THROUGH THE WESTERN GREAT BASIN...TO THE LEE OF THE SIERRA
NEVADA AND SOUTHERN CASCADES...BENEATH A MID-LEVEL THERMAL TROUGH
AXIS...HAS CONTRIBUTED TO SOME DESTABILIZATION AND AT LEAST LOW
PROBABILITIES FOR THUNDERSTORMS. THIS RISK MAY CONTINUE INTO THE
EARLY EVENING HOURS BEFORE DIMINISHING...AIDED BY FORCING ASSOCIATED
WITH A WEAK MID-LEVEL CIRCULATION/TROUGH OVER PARTS OF EASTERN
OREGON INTO NORTHWEST NEVADA.
...SOUTHEAST...
SCATTERED RECENT THUNDERSTORM DEVELOPMENT HAS OCCURRED ACROSS PARTS
OF SOUTHERN GEORGIA...WHERE RELATIVELY HIGH MOISTURE LEVELS HAVE
LINGERED ALONG A POST-FRONTAL CONVERGENCE ZONE...BENEATH A WEAK
CIRCULATION WITHIN A WEAK MID/UPPER TROUGH. HOWEVER...THESE
STORMS...AND MUCH OF THE REMAINING CONVECTIVE DEVELOPMENT ACROSS
INLAND AREAS OF THE FLORIDA PENINSULA...SEEM LIKELY TO DIMINISH BY
OR SHORTLY AFTER 03Z...WITH CONTINUED BOUNDARY LAYER COOLING/
STABILIZATION...AS THE UPPER SYSTEM BEGINS TO PROGRESS OFFSHORE.
..KERR.. 09/18/2008
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