SWODY2
SPC AC 260647
DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1247 AM CST MON DEC 26 2011
VALID 271200Z - 281200Z
...THERE IS A SLGT RISK OF SVR TSTMS PORTIONS COASTAL PLAIN
GA/SC/SRN NC....
...SYNOPSIS...
NRN-STREAM SHORTWAVE TROUGH - NOW EVIDENT IN MOISTURE CHANNEL
IMAGERY OVER NRN ROCKIES -- IS FCST TO MOVE EWD ACROSS NRN PLAINS
DAY-1...TO BE ESSENTIALLY REPLACED BY CLOSELY TRAILING/UPSTREAM
PERTURBATION NOW FARTHER NW OVER BC/AB ROCKIES. BY
27/12Z...TRAILING PERTURBATION WILL DIG SEWD ACROSS MN/IA WHILE LEAD
WAVE DEAMPLIFIES ACROSS ERN ONT. HEIGHT FALLS RELATED TO THIS
PROCESS WILL EXTEND SWD ACROSS CENTRAL PLAINS AND MID-UPPER MS
VALLEY. AS THIS OCCURS...LONG-LIVED MIDDLE-UPPER LEVEL CYCLONE --
NOW MEANDERING ERRATICALLY OVER ERN BORDER OF NM -- IS FCST TO EJECT
EWD OVER RED RIVER REGION AND AR DAY-1. EXPECT OPEN-WAVE TRANSITION
TO BE UNDERWAY WHEN PERTURBATION REACHES MS AND WRN TN BY 27/12Z.
DURING DAY-2...THIS TROUGH WILL DEAMPLIFY CONSIDERABLY...EJECTING
NEWD ACROSS CENTRAL APPALACHIANS AND MID-ATLC REGION. THIS WILL
OCCUR AS TRAILING NRN-STREAM SYSTEM BECOMES PRIMARY ANCHOR FOR
PROGRESSIVE TROUGHING OVER SRN APPALACHIANS AND CAROLINAS. THIS
TROUGH...IN TURN..SHOULD MOVE OFFSHORE CAROLINAS/MID-ATLC REGION
BETWEEN 28/00Z AND 28/12Z.
AT SFC...LOW NOW OVER NWRN GULF WILL MOVE INLAND DAY-1...FAR
OUTPACING POLEWARD PROGRESS OF MARINE/WARM FRONT...AND REACHING NEAR
MID TN OR CENTRAL/ERN KY BY START OF PERIOD. COLD FRONT BY THEN
SHOULD EXTEND SSEWD OVER AL TO WRN PORTIONS FL PANHANDLE. FRONT
SHOULD ACCELERATE EWD ACROSS ERN GULF AND NEWD OVER CENTRAL/SRN
APPALACHIANS AS CYCLONE EJECTS NEWD AND STRENGTHENS OVER MID-ATLC
REGION. BY 28/00Z...FRONT SHOULD EXTEND FROM TRIPLE POINT INVOF
DELMARVA SSWWD OVER NC COAST AND WRN/CENTRAL FL PENINSULA. FRONT
SHOULD CLEAR ALL OF ATLC COAST BUT ERN NEW ENGLAND AS DEEPENING
CYCLONE MOVES NEWD OVER MAINE/SRN QUE REGION.
...SERN CONUS...
BAND OF CONVECTION SHOULD BE ONGOING ALONG OR JUST AHEAD OF SFC COLD
FRONT AT START OF PERIOD...CARRYING OVER MRGL TORNADO AND
WIND-DAMAGE POTENTIAL FROM LAST FEW HOURS OF DAY-1 PERIOD.
IT NOW APPEARS THAT FOREGOING AIR MASS WILL DESTABILIZE SUFFICIENTLY
TO SUPPORT EXTENSION OF AT LEAST MRGL SVR PROBABILITIES SEWD ACROSS
PORTIONS WRN/NRN FL AND SRN GA. PROBABILITIES SUPPORTING
CATEGORICAL SLGT RISK ARE INTRODUCED FARTHER N WHERE STRONGEST
COMBINATION OF SHEAR AND AT LEAST MRGL SFC-BASED INSTABILITY ARE
EXPECTED FROM MIDDAY INTO LATE AFTERNOON LOCAL TIME. AIR MASS
MODIFICATION OVER ERN GULF AND ATLC SHOULD SUPPLY WARM SECTOR WITH
LOW-60S SFC DEW POINTS ACROSS MUCH OF AREA CONTAINING SVR
PROBABILITIES...AS WELL AS POTENTIAL FOR MID-60S OVER WRN FL AND
COASTAL SC/SRN NC. MAIN LIMITING FACTOR WILL BE WEAKNESS OF
LOW-MIDDLE LEVEL LAPSE RATES...KEEPING MLCAPE BELOW 500 J/KG OVER
MOST AREAS.
MEANWHILE...STRONGEST DEEP-LAYER WIND FIELDS AND LOW-LEVEL VERTICAL
SHEAR WILL SHIFT NEWD ACROSS SRN PIEDMONT/COASTAL PLAIN REGION OF
GA/CAROLINAS. PREFRONTAL HODOGRAPHS ARE EXPECTED TO ENLARGE BENEATH
50-60 KT LLJ...COMBINING WITH STG SLY SFC FLOW COMPONENT OFF ATLC
WITH POTENTIAL FOR 0-1 KM SRH 300-500 J/KG. THIS SHOULD SUPPORT
SOME TORNADO POTENTIAL...ALTHOUGH MAIN STORM MODE IS LIKELY TO BE
QUASI-LINEAR.
PRIND WEAKENING OF DEEP-LAYER SHEAR AND LIFT WITH SWD EXTENT...AND
OF BOUNDARY-LAYER INSTABILITY WITH TIME...WILL REDUCE SVR THREAT
OVER ERN/SRN FL RELATIVE TO AREAS FARTHER N AND NW.
..EDWARDS.. 12/26/2011
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