SWODY3
SPC AC 100700
DAY 3 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0200 AM CDT SAT SEP 10 2011
VALID 121200Z - 131200Z
...SYNOPSIS...
DEEP-LAYER CYCLONE NOW OVER MID MS VALLEY REGION SHOULD BECOME
OPEN-WAVE SYNOPTIC TROUGH OVER APPALACHIANS BY EARLY PERIOD...BEST
DEFINED BY EMBEDDED SHORTWAVE TROUGH OVER GA. LATTER PERTURBATION
SHOULD MOVE OFFSHORE GA/CAROLINAS AROUND 13/00Z...WITH TRAILING
PORTION OF TROUGH OVER NRN FL AND NERN GULF. NRN-STREAM SHORTWAVE
TROUGH -- NOW EVIDENT IN MOISTURE CHANNEL IMAGERY OVER NERN PAC S OF
AK...SHOULD MOVE IN CURVING PATH FROM SRN PORTIONS SK/MB ACROSS NRN
ONT AND LS BY 13/12Z. MEANWHILE...PERSISTENT/CUT-OFF CYCLONE SHOULD
MEANDER ERRATICALLY OVER CENTRAL/SRN CA COASTAL AREA...WHILE SLOWLY
FILLING.
AT SFC...CYCLONE ASSOCIATED WITH NRN-STREAM TROUGH SHOULD CROSS NERN
ND/NRN MN REGION EARLY IN PERIOD...PIVOTING EWD ACROSS NRN
WI/LS/UPPER MI REGION TO NERN ONT BY END OF PERIOD. SREF AND
OPERATIONAL MODELS STILL DIFFER WITHIN TEMPORAL/SPATIAL WINDOW OF
4-6 HOURS AND UP TO ABOUT 200 NM ON TIMING/TRACK OF SFC LOW.
TRAILING COLD FRONT WILL MOVE SEWD OVER NRN PLAINS EARLY IN
PERIOD...REACHING SRN MN AND NRN/CENTRAL NEB BY 13/00Z. WARM FRONT
WILL EXTEND FROM LOW EWD ACROSS LS OR ADJOINING UPPER MI DURING
AFTERNOON/EVENING...BEFORE LIFTING NWD INTO ONT. BY 13/12Z...COLD
FRONT SHOULD REACH LOWER MI...NRN IL...NRN MO AND CENTRAL/SRN KS.
REMNANT FRONTAL ZONE WILL LINGER OVER PORTIONS NRN/CENTRAL FL
THROUGH MUCH OF DAY.
...UPPER MS VALLEY TO LS/LM...
SCATTERED TSTMS MAY DEVELOP NEAR SFC LOW AND ADJOINING FRONTAL
SEGMENTS DURING AFTERNOON...WITH POTENTIAL FOR AT LEAST ISOLATED SVR
HAIL/GUSTS. LEADING EDGE OF STRONGEST MID-UPPER
ASCENT/DESTABILIZATION SHOULD BE NEARLY COLLOCATED WITH RELATIVE
MAXIMA IN LOW-LEVEL CONVERGENCE ACCOMPANYING SFC LOW AND NEARBY
COLD-FRONTAL SEGMENT. THIS REGIME WILL IMPINGE UPON AT LEAST MRGLLY
FAVORABLE AND DIABATICALLY HEATED BOUNDARY LAYER DURING AFTERNOON.
SFC DEW POINTS GENERALLY MID-50S TO LOW-60S F AND FAVORABLY STEEP
LAPSE RATES ALOFT WILL SUPPORT MLCAPE IN 1000-2000 J/KG RANGE.
GREATEST VERTICAL SHEAR WILL BE ALONG WARM FRONT AND IN IMMEDIATE
VICINITY OF SFC LOW...WHERE SFC FLOW IS RELATIVELY BACKED...BENEATH
TIGHTENING MID-UPPER LEVEL HEIGHT GRADIENT. SMALLER HODOGRAPHS AND
MORE POTENTIAL FOR QUASI-LINEAR MODE SHOULD CHARACTERIZE
COLD-FRONTAL CONVECTIVE REGIME. STRONGER CAPPING AND WEAKER
CONVERGENCE WILL LESSEN COLD-FRONTAL TSTM POTENTIAL WITH SWWD
EXTENT.
PROGGED DIFFERENCES IN TIMING OF MID-UPPER WAVE AND SFC LOW ARE
MESOSCALE IN NATURE...BUT STILL CRUCIAL TO SPECIFYING ANY CORRIDOR
OF ENHANCED SVR POTENTIAL. ATTM FCST WILL START WITH MRGL
UNCONDITIONAL SVR PROBABILITIES...WITHIN WHICH SMALLER CATEGORICAL
OUTLOOK MAY BE NEEDED IN SUBSEQUENT OUTLOOKS.
..EDWARDS.. 09/10/2011
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