SWODY1
SPC AC 051244
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0744 AM CDT SAT SEP 05 2009
VALID 051300Z - 061200Z
...NO SVR TSTM AREAS FORECAST...
...SYNOPSIS...
A STRONG NRN STREAM SHORTWAVE TROUGH WILL PROGRESS INLAND OVER THE
PAC NW TODAY INTO TONIGHT...WHILE THE PRIMARY BELT OF MID-UPPER
WESTERLIES REMAINS LARGELY N OF THE US/CANADIAN BORDER TO THE E OF
THE NRN ROCKIES. THE NET RESULT WILL BE A BROAD AREA OF WEAK FLOW
OVER MOST OF THE CONUS. ONE WEAK CLOSED LOW OVER MO IS EXPECTED TO
ONLY DRIFT EWD SINCE THIS SYSTEM IS EFFECTIVELY CUTOFF FROM THE MAIN
BELT OF FLOW...AND A WEAK UPPER TROUGH WILL ALSO PERSIST OVER THE
ERN GULF OF MEXICO. SCATTERED THUNDERSTORMS WILL BE FOCUSED OVER
CENTRAL/S FL IN ADVANCE OF THE ERN GULF TROUGH...AS WELL AS THE SRN
MO/NRN AR AREA AROUND THE PERIPHERY OF THE MO CLOSED LOW. FARTHER
W...THE REMNANTS OF A WEAK MID LEVEL TROUGH OVER NV WILL MOVE SLOWLY
EWD OVER NW AZ AND WRN UT DURING THE DAY.
...AZ AREA THIS AFTERNOON...
A BROAD BELT OF MAINLY DIURNAL CONVECTION IS EXPECTED FROM UT SWD
INTO AZ...DOWNSTREAM OF THE WEAK MID LEVEL TROUGH AND WITHIN A
LOW-MID LEVEL MOISTURE PLUME CHARACTERIZED BY PW VALUES OF 0.75-1.25
INCHES. DAYTIME HEATING OVER THE HIGHER TERRAIN WILL HELP FOCUS
STORM DEVELOPMENT DURING THE AFTERNOON...THOUGH CLOUD DEBRIS MAY
DISRUPT SURFACE HEATING ACROSS NRN AZ/SRN UT THE FIRST HALF OF THE
DAY. LOW-MID LEVEL LAPSE RATES MAY ALSO BE REDUCED COMPARED TO
YESTERDAY...AS A RESULT OF PRIOR CONVECTION. THE STRONGER
INSTABILITY IS EXPECTED NEAR AND S OF THE RIM IN AZ...WHERE A GULF
OF CA MOISTURE SURGE WILL HELP MAINTAIN BOUNDARY LAYER DEWPOINTS IN
THE 60S OVER THE LOWER DESERTS THROUGH THE DIURNAL HEATING/MIXING
CYCLE. STILL...A REGIME OF WEAK MID-UPPER WLY FLOW WILL NOT BE
CONDUCIVE TO STORM PROPAGATION FROM THE RIM TO THE LOWER
DESERTS...WHICH SUGGESTS THAT ANY THREAT FOR DAMAGING WINDS WILL BE
RATHER ISOLATED/MARGINAL.
...WRN MT THIS AFTERNOON/EVENING...
MID LEVEL MOISTURE WILL SPREAD NWD FROM THE NRN GREAT BASIN TO WRN
MT AND DEEP LAYER FLOW WILL INCREASE WITH THE APPROACH OF THE PAC NW
SHORTWAVE AND ASSOCIATED BAROCLINIC ZONE. HOWEVER...LOW-LEVEL
MOISTURE WILL BE QUITE LIMITED AHEAD OF THE FRONT...LEAVING
INVERTED-V PROFILES WITH WEAK BUOYANCY DURING THE AFTERNOON WITH
DAYTIME HEATING. THIS ENVIRONMENT MAY SUPPORT A FEW HIGH-BASED
STORMS WITH ISOLATED DAMAGING WIND POTENTIAL...THOUGH THE MARGINAL
LOW-LEVEL MOISTURE WILL LIMIT THE OVERALL SEVERE STORM THREAT.
..THOMPSON/GARNER.. 09/05/2009
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