DAY1SVR: Day 1 Convective Outlook

ACUS01 KWNS 211953
SWODY1
SPC AC 211950

DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0250 PM CDT WED AUG 21 2013

VALID 212000Z - 221200Z

...THERE IS A SLGT RISK OF SVR TSTMS PORTIONS UPPER MIDWEST...UPPER
GREAT LAKES...

...THERE IS A SLGT RISK OF SVR TSTMS PORTIONS CENTRAL
PLAINS...MAINLY NEB...

--- UPDATES ---

...UPPER MIDWEST...UPPER GREAT LAKES...
TSTMS HAVE DEVELOPED INVOF SFC COLD FRONT OVER WRN UPPER MI AND NWRN
WI...AND SHOULD CONTINUE TO GET BETTER ORGANIZED THROUGH REMAINDER
AFTN WHILE MOVING INTO VERY MOIST...DIABATICALLY DESTABILIZED AIR
MASS. PRIMARY RISKS ARE DAMAGING GUSTS AND LARGE HAIL. WHILE
TORNADO POTENTIAL IS NONZERO...IT IS VERY CONDITIONAL ON LOCALIZED
STORM-SCALE/BOUNDARY-INTERACTION PROCESSES GIVEN EXPECTED TENDENCY
TOWARD QUASI-LINEAR STORM MODES AND LACK OF GREATER AMBIENT
LOW-LEVEL SHEAR. MINOR ADJUSTMENTS MADE MAINLY TO PERIPHERAL
PROBABILITY/CATEGORICAL LINES IN DEFERENCE TO CONVECTIVE TRENDS AS
WELL AS POSITION OF LS MARINE LAYER AND OTHER BOUNDARIES. REF WW
494 AND ACCOMPANYING MESOSCALE DISCUSSIONS FOR LATEST GUIDANCE ON
SVR POTENTIAL FROM NERN IA/SERN MN REGION EWD ACROSS WI AND UPPER
MI.

...NRN CA/SRN ORE...
ADDED MRGL HAIL PROBABILITIES IN DEFERENCE TO STRENGTHENING
LARGE-SCALE ASCENT AND DEEP SHEAR AHEAD OF NWD-MOVING MID-UPPER
LEVEL CYCLONE...NOW EVIDENT IN MOISTURE CHANNEL IMAGERY OFFSHORE
CENTRAL CA COAST. REF SPC MESOSCALE DISCUSSION 1746 FOR MORE
DETAILED INFORMATION ON NEAR-TERM POTENTIAL OVER THIS AREA.

...OH VALLEY TO S-CENTRAL APPALACHIANS...
POTENTIAL FOR SPORADIC/ISOLATED DAMAGING GUSTS REMAINS EVIDENT FROM
SRN OH TO NRN TN...WHERE BELT OF SLIGHTLY ENHANCED MIDLEVEL WINDS
AND DEEP SHEAR IS APPARENT E OF MID-UPPER LEVEL CYCLONE MOVING ENEWD
OVER OH VALLEY. REF MESOSCALE DISCUSSIONS 1741 AND 1744 FOR
NEAR-TERM DETAILS OVER THIS REGION.

..EDWARDS.. 08/21/2013

.PREV DISCUSSION... /ISSUED 1129 AM CDT WED AUG 21 2013/

...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.

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