SWODY1
SPC AC 011250
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0750 AM CDT SAT SEP 01 2007
VALID 011300Z - 021200Z
..NO SVR TSTM AREAS FORECAST...
..DAKOTAS/MN THIS AFTERNOON INTO TONIGHT...
A MID LEVEL SHORTWAVE TROUGH OVER NW MT AND SRN ALBERTA WILL CREST
THE MEAN RIDGE OVER THE NRN ROCKIES AND THEN AMPLIFY BY TONIGHT OVER
MANITOBA AND WRN ONTARIO. AN ASSOCIATED SURFACE CYCLONE IS FORECAST
TO PROGRESS EWD FROM SRN SASK AND DEEPEN BY TONIGHT IN WRN ONTARIO
IN ADVANCE OF THE MID LEVEL TROUGH. A REMNANT LEE TROUGH WILL MOVE
EWD INTO THE DAKOTAS THIS AFTERNOON TO THE S OF THE SURFACE
LOW...AND THIS TROUGH WILL BE OVERTAKEN BY A SURFACE COLD FRONT
ACROSS THE DAKOTAS/NW MN. THE SURFACE TROUGH AND COLD FRONT WILL BE
THE PRIMARY FOCUS FOR ANY DEEP CONVECTION THAT DEVELOPS.
SOME MID LEVEL CONVECTION IS ONGOING OVER WRN ND WITHIN A REMNANT
MONSOONAL MOISTURE PLUME...IN ADVANCE OF AN INITIAL/WEAK SHORTWAVE
TROUGH. OTHERWISE...A PLUME OF NEARLY DRY ADIABATIC MID LEVEL LAPSE
RATES IS OVERSPREADING THE NRN PLAINS PER 12Z SOUNDINGS. THE BASE
OF THE ELEVATED MIXED LAYER IS QUITE WARM...WITH AFTERNOON SURFACE
TEMPERATURES OF 95-100 F NECESSARY TO MIX THROUGH THE INVERSION AND
MINIMIZE CONVECTIVE INHIBITION. ADDITIONALLY...SURFACE RIDGING FROM
NEW ENGLAND TO THE SRN PLAINS HAS CUT OFF THE PRIMARY MOISTURE
SOURCE REGION...LEAVING ONLY A SHALLOW MOIST BOUNDARY LAYER WITH
LOW-MID 60S DEWPOINTS ACROSS THE DAKOTAS. IT APPEARS THAT THE CAP
WILL BE SUFFICIENTLY STRONG TO KEEP STORM COVERAGE RATHER
SPARSE...GIVEN THAT THE STRONGER LARGE SCALE FORCING FOR ASCENT WILL
REMAIN N OF THE CANADIAN BORDER. IF THUNDERSTORMS DO FORM ALONG THE
SURFACE TROUGH/FRONT LATE THIS EVENING /MOST PROBABLY ACROSS NW
MN/...GUSTY WINDS AND SOME HAIL WILL BE POSSIBLE.
..RIM COUNTRY OF AZ INTO WRN NM THIS AFTERNOON/EVENING...
SCATTERED THUNDERSTORM DEVELOPMENT IS EXPECTED THIS AFTERNOON OVER
THE HIGHER TERRAIN OVER CENTRAL/WRN NM INTO THE RIM COUNTRY OF AZ.
WEAK NELY FLOW AROUND THE SRN GREAT BASIN HIGH WILL HELP STORMS MOVE
SWWD OFF THE HIGH TERRAIN TOWARD THE LOWER DESERTS IN AZ...WHERE THE
MODIFIED 12Z TUS SOUNDING SUGGESTS SOME POTENTIAL FOR GUSTY OUTFLOW
WINDS THIS AFTERNOON.
..GULF COAST AND SE ATLANTIC STATES...
AN UPPER LEVEL CYCLONIC SHEAR AXIS...WITH EMBEDDED SMALLER SCALE
VORTICITY MAXIMA...WILL PERSIST FROM THE NW GULF COAST TO THE SE
ATLANTIC COAST...ALONG WITH A DIFFUSE SURFACE TROUGH. THESE
FEATURES...ALONG WITH PW IN ADVANCE OF 2 INCHES AND DAYTIME HEATING
OF THE MOIST AIR MASS...WILL PROMOTE THE DEVELOPMENT OF
SCATTERED-NUMEROUS THUNDERSTORMS.
.THOMPSON/BRIGHT.. 09/01/2007
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