SWODY1
SPC AC 071626
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1126 AM CDT MON SEP 07 2009
VALID 071630Z - 081200Z
...NO SVR TSTM AREAS FORECAST...
...SYNOPSIS...
EXCEPT FOR THE PACIFIC NW...THE NRN RCKYS...AND THE NRN HI
PLNS...AREAS THAT WILL LIE BENEATH SRN FRINGE OF BC/AB UPR
LOW...WEAK FLOW WILL PERSIST OVER THE LWR 48 THIS PERIOD. THE
CANADIAN LOW WILL CONTINUE ENE INTO NRN AB EARLY TUE AS ASSOCIATED
SPEED MAX NOW ENTERING NRN CA/SRN ORE REACHES SW MT. ELSEWHERE...
CYCLONIC SHEAR AXIS PRECEDING THE LOW...NOW EXTENDING FROM WRN SD TO
SE CO...SHOULD ADVANCE VERY SLOWLY E AS WEAK UPR LOW LINGERS OVER
THE MID OH VLY. FARTHER E...A WEAKER UPR CIRCULATION WILL EDGE NNE
ALONG THE NC CST.
COLD FRONT WITH BC/AB SYSTEM SHOULD MOVE SLOWLY E/SE ACROSS THE WRN
DAKOTAS...PRECEDED BY LEE TROUGH OVER WRN SD/WRN NEB/NE CO. SFC
FEATURES WILL REMAIN DIFFUSE E OF THE MS RVR...WITH THE EXCEPTION OF
FRONTAL ZONE OFF THE CAROLINA CST. THIS BOUNDARY SHOULD REMAIN
MOSTLY OFFSHORE...ALTHOUGH IT MIGHT ADVANCE NW ACROSS THE OUTER
BANKS TONIGHT/EARLY TUE.
...NRN HI PLNS THIS AFTN INTO TONIGHT...
SFC HEATING WILL YIELD MODERATE INSTABILITY ALONG COLD FRONT/LEE
TROUGH OVER ND AND WRN SD/NEB TODAY. SFC DEWPOINTS NEAR 60 F
BENEATH EML SHOULD SUPPORT SBCAPE AROUND 1000 J/KG IN ND...AND 2000
J/KG IN NEB. WEAK FLOW WILL MINIMIZE DEEP SHEAR...WITH THE
EXCEPTION OF WRN/NRN ND...WHERE VALUES MAY REACH 30 KTS ON SRN
FRINGE OF SWLY UPR JET. THUS...ANY SFC-BASED STORMS THAT FORM ALONG
COLD FRONT OR LEE TROUGH THIS AFTN/EVE SHOULD BE MULTICELLS...WITH
AN ATTENDANT THREAT FOR ISOLD SVR HAIL/WIND GIVEN MAGNITUDE OF CAPE.
POST-FRONTAL ELEVATED CONVECTION NOW OVER WRN ND SHOULD DIMINISH
LATER TODAY. ADDITIONAL ELEVATED TSTMS LIKELY WILL FORM TONIGHT
OVER WY/SRN MT IN WAKE OF FRONT AS ASCENT INCREASES DOWNSTREAM FROM
PREVIOUSLY-MENTIONED SPEED MAX. A MARGINAL SVR THREAT WILL EXIST
WITH THESE STORMS AS THEY SPREAD NE INTO WRN ND/NW SD THROUGH EARLY
TUE...WHERE A NARROW CORRIDOR OF 30+ KT CLOUD LAYER SHEAR WILL
DEVELOP IN THE PRESENCE OF 500-1000 J/KG ELEVATED CAPE.
...NC OUTER BANKS...
SHOWERS/WEAK TSTMS SHOULD CONTINUE ALONG AND N/W OF NEARLY STNRY
FRONT OFF THE NC CST THROUGH TUE MORNING. WIND PROFILES WITH
SUBSTANTIAL LOW LVL VEERING WILL PERSIST...AS WILL DEEPLY MOIST
ENVIRONMENT. THIS SETUP MAY FOSTER DEVELOPMENT OF SCTD CELLS WITH
OCCASIONAL LOW LVL ROTATION. OVERALL SETUP SUGGESTS THAT THE
STRONGEST/MOST PERSISTENT OF ANY SUCH ACTIVITY WILL REMAIN OFFSHORE
THROUGH THE PERIOD. HOWEVER...AN ISOLD TORNADO CANNOT BE RULED OUT
ALONG THE NC OUTER BANKS AS FRONT CREEPS SLOWLY NWWD LATER IN THE
PERIOD.
...ELSEWHERE...
SCTD DIURNAL STORMS EXPECTED ALONG CNTRL GULF CST...OVER S FL... AND
OVER THE CNTRL/SRN RCKYS. A CONCENTRATED AREA OF STORMS ALSO MAY
FORM WITH AFTN HEATING FROM SRN OH SWD INTO ERN KY/TN AHEAD OF MID
OH VLY UPR LOW. POOR LAPSE RATES AND/OR WEAK FLOW SHOULD PRECLUDE
AN ORGANIZED SVR THREAT IN THESE AREAS. COMPARATIVELY STEEP LOW TO
MID LVL LAPSE RATES AND AMPLE MOISTURE MAY SUPPORT WDLY SCTD STG
STORMS AHEAD OF UPR DISTURBANCE NOW APPROACHING W TX. ABSENCE OF AN
OBVIOUS LOW LVL FOCUSING MECHANISM AND WEAK SHEAR
SUGGEST...HOWEVER...THAT ANY STG STORMS THAT DO INDEED FORM WILL
REMAIN ISOLD/SHORT-LIVED.
..CORFIDI/SMITH.. 09/07/2009
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