SPC AC 211629

   DAY 1 CONVECTIVE OUTLOOK  
   NWS STORM PREDICTION CENTER NORMAN OK
   1129 AM CDT WED AUG 21 2013

   VALID 211630Z - 221200Z

   ...THERE IS A SLGT RISK OF SVR TSTMS OVER PARTS OF THE UPR MS
   VLY/UPR GRT LKS...

   ...THERE IS A SLGT RISK OF SVR TSTMS OVER PARTS OF THE CNTRL PLNS...

   ...SYNOPSIS...
   MODERATE...LOW-AMPLITUDE CYCLONIC FLOW WILL PERSIST ACROSS S CNTRL
   CANADA THIS PERIOD...ON NRN FRINGE OF BROAD RIDGE CENTERED OVER
   CNTRL PORTIONS OF THE RCKYS AND PLNS. POSITIVE-TILT SHORTWAVE TROUGH
   IN THE CANADIAN JET...NOW ENTERING WRN ONT...SHOULD REACH THE AREA N
   OF LK SUPERIOR THIS EVE...BEFORE CONTINUING E INTO WRN QUE EARLY
   THU. ELSEWHERE...E PACIFIC UPR LOW EXPECTED TO CONTINUE EDGING E
   TOWARD SFO...WHILE WEAKER SYSTEM DEVOLVES INTO AN OPEN TROUGH OVER
   THE OH VLY.

   AT LWR LVLS...COLD FRONT ASSOCIATED WITH THE ONT TROUGH WILL
   PROGRESS ESE ACROSS THE UPR MS VLY/UPR GRT LKS...WHILE BECOMING
   STNRY OVER CNTRL/SRN NEB. THE BOUNDARY LIKELY WILL BE THE MAIN FOCUS
   FOR STRONG TO POTENTIALLY SVR TSTM DEVELOPMENT THIS PERIOD.

   ...UPR MS VLY/UPR GRT LKS THIS AFTN/EVE...
   GIVEN RICH MOISTURE OVER REGION /PW AROUND 1.75 IN/...STRONG SFC
   HEATING AND FRONTAL UPLIFT SHOULD BE SUFFICIENT TO OVERCOME CIN AND
   SUPPORT SCTD TSTM DEVELOPMENT ALONG COLD FRONT CROSSING SE
   MN...NRN/CNTRL WI...AND UPR MI LATER TODAY. DEEP EML SAMPLED BY THE
   12Z MSP RAOB SUGGESTS POTENTIAL FOR STRONG SFC-BASED BUOYANCY...WITH
   POCKETS OF MLCAPE AOA 2500 J/KG POSSIBLE BY LATE AFTN. WHILE IMPACT
   OF THE ONT UPR TROUGH WILL BE MINIMAL S OF THE CANADIAN
   BORDER...SATELLITE AND MODEL DATA SUGGEST THAT AT LEAST SOME DEGREE
   OF ANCILLARY LARGE-SCALE ASCENT WILL GLANCE WI/UPR MI. COUPLED WITH
   25-30 KT WNWLY 700-500 MB FLOW...OVERALL SETUP COULD YIELD A FEW
   CLUSTERS OF SUSTAINED MULTICELLS...TRANSIENT SUPERCELLS...AND BOWING
   SEGMENTS WITH A RISK FOR LARGE HAIL/DMGG WIND AND POSSIBLY A TORNADO
   THROUGH EARLY TNGT.

   ...CNTRL PLNS THIS AFTN/EVE...
   A SEPARATE AREA OF ENHANCED SVR THREAT MAY EVOLVE LATE THIS AFTN
   INTO TNGT OVER PARTS OF NEB...WHERE LOW-LVL WAA WILL MAXIMIZE NEAR
   STALLING SFC FRONT. ELY LOW-LVL WINDS N OF THE BOUNDARY BENEATH BAND
   OF ENHANCED /25 KT/ WLY MID-LVL FLOW ON IMMEDIATE N SIDE OF THE UPR
   RIDGE WILL YIELD WIND PROFILES FAVORABLE FOR ORGANIZED/SUSTAINED
   STORMS. THESE WILL BE CAPABLE OF SVR HAIL
   AND WIND AS HEATING BOOSTS MLCAPE TO AOA 1500 J/KG. STALLING OF THE
   FRONT AND EXPECTED NOCTURNAL INCREASE OF SLY LLJ SUGGEST LIKELIHOOD
   FOR UPSCALE GROWTH INTO A SIZABLE MCS OR TWO TNGT...WITH A GRADUALLY
   DIMINISHING SVR RISK.

   ...NRN CA/SRN ORE/NW NV THIS AFTN/EVE...
   LARGE SCALE ASCENT AND MID/UPR-LVL UPR FLOW WILL GRADUALLY INCREASE
   ACROSS PARTS OF CA/ORE/NV TODAY THROUGH EARLY THU AS OFFSHORE LOW
   EDGES E TOWARD REGION. DAYTIME HEATING COUPLED WITH MODEST MOISTURE
   /PW UP TO 1 IN/ WILL YIELD SBCAPE SUFFICIENT FOR DIURNALLY-ENHANCED
   SHOWERS/TSTMS...MAINLY OVER THE HIGHER TERRAIN. THESE COULD YIELD
   ISOLD INSTANCES OF SVR WIND/HAIL. WITH SHEAR/UPR DIVERGENCE EXPECTED
   TO CONTINUE INCREASING THROUGH EARLY THU...ESPECIALLY OVER NRN
   CA...A CONDITIONAL ISOLD SVR RISK MAY CONTINUE THROUGH THE END OF
   THE PERIOD.

   ...ERN KY/WRN WV AREA THIS AFTN...
   A FEW STORMS WITH LOCALLY DMGG WIND AND/OR MARGINAL HAIL MAY DEVELOP
   THIS AFTN ON ERN FLANK OF SLOWLY-PROGRESSIVE UPR LOW/TROUGH...WHERE
   UPDRAFT STRENGTH WILL BE ENHANCED BY RELATIVELY COOL MID-LVL TEMPS
   /MINUS 10 C AT 500 MB/ AND STORM ORGANIZATION FOSTERED BY BAND OF
   DCVA/UPR DIVERGENCE.

   ..CORFIDI/COHEN.. 08/21/2013

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