SWODY3
SPC AC 090640
DAY 3 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0140 AM CDT FRI SEP 09 2011
VALID 111200Z - 121200Z
...SYNOPSIS...
BLOCKY MID-UPPER LEVEL PATTERN FCST TO EVOLVE SLIGHTLY THROUGH
PERIOD...PRIMARILY OVER ERN CONUS. BROAD/DEEP-TROPOSPHERIC CYCLONE
NOW ANALYZED OVER OH VALLEY IS EXPECTED TO WEAKEN TO OPEN-WAVE
CHARACTER DAY-3. ALTHOUGH OPERATIONAL PROGS AND SREF MEMBERS DIFFER
ON SHORTWAVE DETAILS...THEY AGREE WELL ON GEN CONCEPT OF POSITIVELY
TILTED AND DEAMPLIFYING SYNOPTIC SCALE TROUGH BY END OF
PERIOD...EXTENDING FROM LOWER GREAT LAKES OR INTERIOR MID-ATLANTIC
REGION SWD ACROSS SRN APPALACHIANS TO N-CENTRAL GULF.
MEANWHILE...CUT-OFF MID-UPPER LOW INVOF S-CENTRAL CA
COAST...DISCUSSED IN DAY-2 OUTLOOK...SHOULD FILL SLOWLY WHILE
REMAINING ESSENTIALLY IN PLACE.
IN RESPONSE TO APCHG TROUGH ALOFT...WEAK FRONTAL-WAVE LOW MAY
DEVELOP LATE DAY-2 OR EARLY THIS PERIOD ALONG QUASISTATIONARY
FRONTAL ZONE NOW OVER CENTRAL FL PENINSULA. THAT PORTION OF THIS
BOUNDARY E AND NE OF SFC LOW SHOULD LIFT NWD TOWARD AND PERHAPS
ACROSS SC AND SRN NC COAST AS WARM FRONT...WHILE TRAILING BOUNDARY
BECOMES MORE SSW-NNE ALIGNED ACROSS WRN/NRN FL.
...COASTAL CAROLINAS/GA...
CONDITIONAL POTENTIAL FOR SVR EXISTS OVER THIS REGION...MAINLY
ASSOCIATED WITH SFC LOW...WARM FRONT AND ANY PORTION OF ADJOINING
WARM SECTOR THAT CAN MOVE INLAND. SERN FRINGE OF STRONGEST
MID-UPPER WINDS -- I.E. 50-60 KT AT 250 MB AND 35-45 KT AT 500 MB --
IS FCST TO SHIFT OVER THIS AREA THROUGH DAY...AS HEIGHT GRADIENT
ALOFT TIGHTENS WITH APCH OF SYNOPTIC TROUGH. MEANWHILE...MOST
AGGRESSIVE MODEL SCENARIOS OF OPERATIONAL WRF...ETA-KF AND ABOUT 1/2
OF SREF MEMBERS INDICATE HIGH-SRH WARM FRONTAL ZONE OVER COASTAL
GA/SC DURING LATE AFTERNOON AND EARLY EVENING. ALONG AND SE OF
FRONT...EXPECT SFC DEW POINTS 70S F...SFC-BASED EFFECTIVE INFLOW
PARCELS...AND FAVORABLE HODOGRAPHS FOR SUPERCELLS. MAIN
UNCERTAINTIES ATTM INVOLVE QUALITY OF INLAND BOUNDARY-LAYER AIR
MASS...WHICH WILL DEPEND STRONGLY ON ACTUAL WARM-FRONTAL PENETRATION
INLAND AND RECOVERY FROM EARLIER CONVECTION OVER AREA. GIVEN SUCH
MESOSCALE UNCERTAINTIES THIS FAR OUT IN TIME...ONLY 5% UNCONDITIONAL
SVR PROBABILITIES ARE WARRANTED.
...MID-ATLANTIC TO CENTRAL APPALACHIANS...
TSTMS MAY DEVELOP DURING DAY WHEREVER COMBINATION OF RESIDUAL
LOW-LEVEL MOISTURE AND STG SFC HEATING CAN OFFSET WEAK LAPSE RATES
ALOFT. THOUGH UPPER-LEVEL FLOW SHOULD BE STG...LIKELY WEAKNESS OF
BOTH FLOW AND SHEAR IN LOW-MIDDLE LEVELS INDICATES LACK OF ORGANIZED
SVR THREAT.
..EDWARDS.. 09/09/2011
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