OV Severe Weather Nov. 22?

[Tim from Springfield (IL)]

The OV now is in play for severe weather this Tuesday, Nov. 22--SPC Day 3 slight risk now reaches far southern parts of IN and OH.

http://www.spc.noaa....k/day3otlk.html

DAY 3 CONVECTIVE OUTLOOK NWS STORM PREDICTION CENTER NORMAN OK 0216 AM CST SUN NOV 20 2011 VALID 221200Z - 231200Z ...THERE IS A SLGT RISK OF SVR TSTMS PORTIONS CENTRAL/WRN GULF COAST TO SRN APPALACHIANS AND OH VALLEY... ...SYNOPSIS... STG SHORTWAVE TROUGH AND EMBEDDED MID-UPPER LOW -- NOW EVIDENT IN MOISTURE CHANNEL IMAGERY OFFSHORE CA -- IS FCST TO MOVE EWD ACROSS GREAT BASIN...SRN ROCKIES AND SRN HIGH PLAINS THROUGH DAY-2. BY START OF PERIOD...THIS SYSTEM SHOULD ASSUME POSITIVE TILT AT 500 MB...ROUGHLY FROM ERN KS SWWD TO W-CENTRAL TX. ALTHOUGH OPERATIONAL MODELS AND SREF MEMBERS START TO DIVERGE WITH AMPLITUDE AND SPEED OF THIS PERTURBATION LATE DAY-2 INTO EARLY DAY-3...DIFFERENCES NOW APPEAR MESOSCALE IN NATURE THROUGH THIS PERIOD. MID-UPPER TROUGH SHOULD EXTEND FROM CENTRAL/SRN IL TO CENTRAL/ERN TX BY 23/00Z...AND FROM OH SWWD OVER AL BY 23/12Z. AT SFC...FRONTAL-WAVE CYCLONE SHOULD MOVE FROM SERN MO ENEWD ACROSS LOWER GREAT LAKES/NRN APPALACHIANS REGION THROUGH PERIOD. COLD FRONT SHOULD EXTEND FROM LOW SWWD ACROSS SERN OK AND CENTRAL/SW TX BY 22/12Z...THEN FROM SRN INDIANA TO WRN/MID TN AND CENTRAL/SRN LA BY 23/00Z. FRONT SHOULD REACH CENTRAL/SRN APPALACHIANS AND WRN FL PANHANDLE BY END OF PERIOD.

...CENTRAL/WRN GULF COAST TO SRN APPALACHIANS AND OH VALLEY... LATE DAY-2 INTO EARLY DAY-3...EXPECT BAND OF TSTMS TO BUILD SWWD ALONG SFC COLD FRONT...WITH ATTENDANT RISK FOR OCNL DAMAGING GUSTS AND ISOLATED HAIL FROM OZARKS TO CENTRAL/ERN TX. THROUGH LATE AFTERNOON...SVR RISK SHOULD SHIFT EWD...WHILE EXPANDING NWD OVER OH VALLEY IN STEP WITH EXPANDING WARM-SECTOR REGIME OF AT LEAST MRGL BUOYANCY. CONVECTION ALSO SHOULD BACKBUILD ALONG/AHEAD OF FRONT TOWARD COASTAL SE TX AND LA. DAMAGING TSTM GUSTS SHOULD REMAIN MOST PREVALENT SVR MODE DURING AFTERNOON/EVENING...THOUGH TORNADOES AND ISOLATED HAIL ALSO ARE POSSIBLE. MAIN UNCERTAINTIES RESULT FROM DIFFERENCES IN PROGS OF SYSTEM SPEED...AND INVOLVE BOTH TIMING OF SVR THREAT AREA-WIDE...AND NWD EXTENT OF SVR THREAT INTO OH VALLEY REGION. SVR THREAT THEREFORE IS MORE CONDITIONAL WITH NWD AND EWD EXTENT WHERE AVAILABILITY OF SFC-BASED EFFECTIVE LIFTED PARCELS IS PROGRESSIVELY MORE QUESTIONABLE. WARM-SECTOR AIR MASS WILL DESTABILIZE DIURNALLY FROM COMBINATION OF BOUNDARY-LAYER THETAE ADVECTION AND POCKETS OF SFC DIABATIC HEATING. EXPECT SFC DEW POINTS RANGING FROM LOWER 60S NEAR OH RIVER TO UPPER 60S/LOW 70S OVER COASTAL AREAS OF LA/MS/AL. FCST SOUNDINGS SUGGEST THIS WILL OFFSET MODEST MIDLEVEL LAPSE RATES ENOUGH FOR MLCAPE 1000-1500 J/KG FROM GULF COAST TO TN VALLEY REGION...DIMINISHING TO BELOW 500 J/KG OVER OH RIVER. DOMINANT CONVECTIVE MODE SHOULD REMAIN QUASI-LINEAR...AS WINDS ALOFT PRECEDING POSITIVELY-TILTED TROUGH CROSS LOW-LEVEL CONVERGENCE ZONE AT SMALL ANGLE. HOWEVER...WITH LACK OF SIGNIFICANT ELEVATED MIXED-LAYER AIR MASS AHEAD OF FRONT...MLCINH SHOULD BE RATHER SMALL. THIS MAY PERMIT DISCRETE OR CLUSTERED DEVELOPMENT AHEAD OF MAIN LINE...WITH ENOUGH DEEP-LAYER SHEAR TO SUPPORT CONDITIONAL SUPERCELL POTENTIAL AHEAD OF MAIN BAND...IN ADDITION TO ANY EMBEDDED SUPERCELLS/BOWS/MESOVORTICES IN QLCS. CONVECTIVE REGIME WILL SHIFT EWD ACROSS LOWER DELTA...MID-SOUTH...OH VALLEY AND TN VALLEY REGIONS THROUGH EVENING...IN STEP WITH OR SLIGHTLY AHEAD OF SFC COLD FRONT. DURING LATE EVENING AND OVERNIGHT HOURS...FAVORABLE BUOYANCY WILL BE OVERTAKEN FROM N-S AS MAIN TSTM BAND ENCOUNTERS MORE STABLE BOUNDARY-LAYER TRAJECTORIES EMANATING FROM RIDGING OVER ATLANTIC COAST REGION. SVR POTENTIAL ACCORDINGLY SHOULD DIMINISH OVER NRN PORTIONS OF OUTLOOK AREA...AND BECOME MORE CONDITIONAL/MRGL EWD ACROSS ERN PORTIONS AL/TN INTO WRN GA. ..EDWARDS.. 11/20/2011

[janetjanet998]

thread in main forum that will cover sveral subforums

http://www.americanw...-weather-event/