SWODY2
SPC AC 100546
DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1246 AM CDT SAT SEP 10 2011
VALID 111200Z - 121200Z
...NO SVR TSTM AREAS FORECAST...
...SYNOPSIS...
PERSISTENT/DEEP-LAYER CYCLONE NOW OVER MID MS AND LOWER OH VALLEYS
IS EXPECTED TO BECOME OPEN-WAVE/POSITIVELY-TILTED TROUGH EARLY-MID
DAY-2 PERIOD. BY 12/00Z...500-MB TROUGH SHOULD EXTEND FROM LOWER
GREAT LAKES SWWD ACROSS OH...TN AND LA TO NWRN GULF. BY END OF
PERIOD...TROUGH SHOULD RESIDE OVER APPALACHIANS FROM NY-GA THEN
OFFSHORE MS RIVER MOUTH. BASAL SHORTWAVE TROUGH WILL PIVOT
CYCLONICALLY FROM AR-GA THROUGH PERIOD. FARTHER NW...MOISTURE
CHANNEL IMAGERY INDICATES SHORTWAVE TROUGH OVER SRN GULF OF AK.
THIS FEATURE SHOULD PENETRATE WRN NORTH AMERICAN MEAN RIDGE
DAY-1...REACHING SRN PARTS OF SK/MB BY 12/12Z. CUT-OFF MID-UPPER
CYCLONE SHOULD DRIFT ERRATICALLY OVER PORTIONS CENTRAL/SRN CA AND
ADJACENT COASTAL WATERS THROUGH PERIOD.
AT SFC...INITIALLY QUASISTATIONARY FRONTAL ZONE OVER N-CENTRAL FL
PENINSULA IS FCST TO PIVOT CYCLONICALLY THIS PERIOD AS APCHG
MID-UPPER WAVE STIMULATES WEAK FRONTAL-WAVE LOW FORMATION AT SFC.
ALTHOUGH PROGS STILL ARE RATHER INCONSISTENT ABOUT TIMING/LOCATION
OF THIS WAVE-LOW DEVELOPMENT...PATTERN SUPPORTS LOW POSITION OVER
SRN GA/NRN FL REGION...CONSISTENT WITH LATEST/00Z OPERATIONAL WRF
AND PRIOR/12Z ECMWF RUN. DURING LATTER HALF OF PERIOD...MOVEMENT OR
REFORMATION OF WARM FRONT IS EXPECTED EITHER OVER COASTAL AREAS OF
GA/SC...OR JUST OFFSHORE.
...MID-ATLANTIC TO UPPER OH RIVER REGION...
SCATTERED TSTMS IN CLUSTERS SHOULD DEVELOP DURING AFTERNOON...WITHIN
BROAD PLUME OF RESIDUAL BOUNDARY-LAYER MOISTURE CHARACTERIZED BY 60S
F SFC DEW POINTS. ISOLATED STG/DAMAGING GUSTS ARE POSSIBLE...THOUGH
SVR THREAT DOES NOT APPEAR WELL-ORGANIZED. MOST FAVORABLE
DEEP-LAYER FLOW SHOULD BE E OF APPALACHIANS TO MID-ATLANTIC
COAST...ALONG NWRN FRINGES OF MID-UPPER JET. WHILE TSTMS WILL BE
POSSIBLE AS FAR SW AS LOWER MS VALLEY...LOW-MIDLEVEL WINDS AND
DEEP-LAYER SHEAR EACH SHOULD WEAKEN WITH WWD EXTENT FROM PA ACROSS
OH AND REMAIN QUITE WEAK FARTHER SW.
...COASTAL GA/SC/NC...
SVR POTENTIAL DEPENDS STRONGLY ON POSITION OF RELATIVELY
HIGH-VORTICITY/HIGH-SRH WARM-FRONTAL CORRIDOR AND ITS SFC-BASED
EFFECTIVE INFLOW PARCELS...WITH RESPECT TO COAST. FCST SOUNDINGS
SUGGEST SUFFICIENTLY LARGE HODOGRAPHS FOR SUPERCELLS ALONG FRONT.
FROM LATE AFTERNOON THROUGH OVERNIGHT HOURS...CORRIDOR WILL LIE
BENEATH ERN RIM OF MID-UPPER JET FEATURING 70-90 KT 250-MB WINDS AND
40-45 KT 500-MB FLOW...CONTRIBUTING TO FAVORABLE DEEP-LAYER SHEAR.
WILL MAINTAIN MRGL UNCONDITIONAL PROBABILITIES ACROSS THIS REGION
GIVEN UNCERTAINTIES REMAINING OVER MESOBETA-SCALE BOUNDARY
POSITIONING THAT IS CRUCIAL TO ACTUAL SVR THREAT.
...NRN PORTIONS ND/MN...
AFTER 12/06Z...NARROW BUT STG BELT OF LARGE-SCALE ASCENT...BOTH IN
FORM OF LOW-LEVEL WAA AND MID-UPPER DCVA...SHOULD IMMEDIATELY
PRECEDE MID-UPPER LEVEL SHORTWAVE TROUGH ACROSS SRN PRAIRIE
PROVINCES. LOW-LEVEL MOISTURE WILL BE MRGL BUT SUFFICIENT TO
SUPPORT TSTMS IN THIS REGIME...SOME OF WHICH MAY PRODUCE HAIL. MOST
OF THE CONVECTION SHOULD REMAIN JUST N OF CANADIAN BORDER. SRN
FRINGE OF ACTIVITY MAY BRUSH ACROSS NRN MN/ND NEAR END OF PERIOD.
ATTM SVR POTENTIAL IS TOO CONDITIONAL/SMALL FOR AOA 5% LINE.
..EDWARDS.. 09/10/2011
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