SPC AC 010602
DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0102 AM CDT WED APR 01 2009
VALID 021200Z - 031200Z
...THERE IS A MDT RISK OF SVR TSTMS PORTIONS LOWER MS VALLEY AND
SWRN TN TO WRN FL PANHANDLE AND SWRN GA....
...THERE IS A SLGT RISK OF SVR TSTMS ELSEWHERE FROM ARKLATEX REGION
TO PORTIONS CAROLINAS AND NRN FL...
SIGNIFICANT OUTBREAK OF SVR TSTMS -- INCLUDING POTENTIAL FOR
STRONG/LONG-TRACK TORNADOES AND WIDESPREAD DAMAGING WIND -- APPEARS
INCREASINGLY PROBABLE THURSDAY ACROSS MUCH OF DIXIE. GREATEST
THREAT AREA IS EVIDENT FROM LOWER MS VALLEY/DELTA REGION EWD ACROSS
MS/AL TO PARTS OF WRN GA. CONDITIONAL POTENTIAL EXISTS FOR THIS
EVENT TO EXTEND NWD ACROSS MORE OF MID-SOUTH REGION DURING DAYLIGHT
HOURS...AND/OR EWD TOWARD SRN PIEDMONT/CAROLINAS LATE IN PERIOD.
...SYNOPSIS...
UPPER AIR PATTERN WILL REMAIN CHARACTERIZED BY LARGE SCALE TROUGH
OVER CENTRAL CONUS...AND RIDGING OVER E COAST AND NERN PACIFIC.
PROGRESSIVE SERIES OF TROUGHS WILL CONTINUE TO PERTURB THAT PATTERN
ON SHORTWAVE SCALE. MID-UPPER LEVEL LOW -- NOW ANALYZED OVER SRN MN
-- IS FCST TO EJECT NWD ACROSS NRN ONT AND WEAKEN THIS PERIOD.
ASSOCIATED SFC COLD FRONT -- INITIALLY ANALYZED FROM WRN KY SWD
ACROSS SERN MS...EXTREME SERN LA AND NWRN GULF -- IS FCST TO RETURN
NWD ACROSS GULF COAST EARLY DAY-2 PERIOD AS WARM FRONT. WRN SEGMENT
OF WARM FRONT SHOULD RETREAT NWD ACROSS PORTIONS MS/AL AND PERHAPS
WRN TN BEFORE COLD FROPA. ERN SEGMENT OF WARM FRONT -- INVOF FL
PANHANDLE AND ADJACENT WATERS EWD ACROSS SRN FL - MAY BE MODULATED
BY SERIES OF CONVECTIVE COMPLEXES THAT SHOULD OCCUR THROUGH DAY-1
AND EARLY DAY-2 PERIODS. THUS...NWD RETREAT OF WARM FRONT ACROSS
THAT REGION NWD OVER GA/CAROLINAS MAY BE DELAYED UNTIL LATE IN
PERIOD...AND IS UNCERTAIN IN NWD EXTENT.
RETURN FLOW WILL BE OCCURRING IN ADVANCE OF NEXT MID-UPPER SHORTWAVE
TROUGH -- NOW DIGGING SEWD ACROSS NRN ROCKIES AND NRN UT. THIS
FEATURE SHOULD STRENGTHEN CONSIDERABLY...EVOLVING INTO COMPACT BUT
INTENSE TROUGH WITH EMBEDDED CLOSED LOW OVER OK BY 02/12Z. THIS
POSITION...AND SUBSEQUENT FCST TRACK ENEWD ACROSS AR BY 03/12Z...IS
SLIGHTLY FARTHER N THAN PREVIOUS PROGS...BUT WITH VERY STG AGREEMENT
AMONG AVAILABLE OPERATIONAL MODELS AND SREF CONSENSUS. TROUGH THEN
SHOULD EJECT NEWD ACROSS WRN TN...WRN/CENTRAL KY AND LOWER OH
VALLEY...REACHING OH/WV NEAR END OF PERIOD. ASSOCIATED SFC CYCLONE
-- INITIALLY OVER OK JUST AHEAD OF 500 MB LOW -- SHOULD DEEPEN
THROUGH DAYLIGHT HOURS AS IT MOVES TO WRN KY/SRN IL
AREA...OCCLUDE...THEN EJECT TOWARD NWRN OH/SERN LOWER MI/NERN
INDIANA AREA. TRAILING SFC COLD FRONT WILL SWEEP EWD FROM CENTRAL
TX/SRN OK POSITION AT 2/12Z...TO WRN TN...WRN/CENTRAL MS AND SERN LA
BY 3/00Z...THEN FROM WRN CAROLINAS TO ERN FL PANHANDLE BY 3/12Z.
...ARKLATEX TO WRN GA AND MID-SOUTH...
PRIOR NOCTURNAL SVR POTENTIAL DESCRIBED IN DAY-1 OUTLOOK IS FCST TO
CARRY OVER INTO MORNING HOURS AND SHIFT EWD ACROSS THIS REGION.
LARGE HAIL SHOULD BE MAIN INITIAL THREAT...WITH DAMAGING
WIND/TORNADOES BECOMING INCREASINGLY PROBABLE THROUGHOUT DAYLIGHT
HOURS AS FOREGOING BOUNDARY AIR MASS DESTABILIZES FROM COMBINATION
OF WAA...MOIST ADVECTION AND SFC DIABATIC HEATING. S OF WARM
FRONT...MARINE AIR MASS WILL BE CHARACTERIZED BY SFC DEW POINTS
MID/UPPER 60S F WITH SPOTTY 70S...BENEATH INCREASINGLY STEEP
MIDLEVEL LAPSE RATES AND INTENSE DEEP-LAYER SHEAR. ACCORDINGLY
MODIFIED FCST SOUNDINGS YIELD MLCAPES 2000-3000 J/KG FROM MID-DAY
THROUGH LATE AFTERNOON AHEAD OF COLD FRONT.
WARM SECTOR FLOW MAY BE SOMEWHAT VEERED...I.E. SSWLY TO
SWLY...REDUCING DIRECTIONAL SHEAR SOMEWHAT WITH STRONGEST
ISALLOBARIC FORCING PROGGED AHEAD OF SFC CYCLONE OVER OH VALLEY.
NONETHELESS...VERY STG MID-UPPER WINDS...INCLUDING 80-90 KT 500 MB
SPEED MAX...SHOULD SHIFT EWD FROM LA TO GA...YIELDING EFFECTIVE
SHEAR VALUES 60-70 KT OVER SAME AREAS AS LARGEST BUOYANCY -- I.E.
CATEGORICAL MDT RISK OUTLOOK. GIVEN LACK OF GREATER DIRECTIONAL
SHEAR...ACTIVITY NEAR COLD FRONT MAY BE QUASI-LINEAR...BUT PROGGED
COMPONENT OF MEAN WIND ACROSS FRONT ALSO SUGGESTS POTENTIAL FOR
EMBEDDED/SEMI-DISCRETE SUPERCELLS AND DAMAGING BOW/LEWP FEATURES.
LARGEST LOW-LEVEL HODOGRAPHS WILL BE ALONG WARM FRONT...WHERE 0-1 KM
SRH SHOULD EXCEED 250 J/KG. ANY DISCRETE/SUSTAINED STORMS MOVING
THROUGH WARM SECTOR...OR INTERACTING WITH BACKED WINDS ALONG WARM
FRONT...MAY POSE SIGNIFICANT TORNADO RISK. RELATIVE MIX OF
CONVECTIVE MODES...AND COVERAGE OF STORMS AHEAD OF FRONTAL
BAND...REMAIN PRIMARY UNCERTAINTIES ATTM.
INSTABILITY WILL DECREASE WITH NWD EXTENT ACROSS MID-SOUTH REGION
INTO OH VALLEY...THOUGH AT LEAST ONE NARROW BAND OF SVR TSTMS
APPEARS LIKELY INVOF COLD FRONT.
...SERN CONUS...GA TO CAROLINAS...
MULTIPLE ROUNDS OF STG-SVR CONVECTION MAY OCCUR INVOF RETURNING WARM
FRONTAL ZONE THROUGHOUT PERIOD...WITH ACCOMPANYING RISK FOR
SVR...AMIDST INCREASING DEEP-LAYER SHEAR. NOCTURNAL POTENTIAL WILL
INCREASE FROM W AS STRENGTHENING MID-UPPER WINDS AND LOW LEVEL WAA
YIELD MORE FAVORABLE SHEAR/BUOYANCY COMBINATION...AND HODOGRAPH SIZE
INCREASES BENEATH NOCTURNAL LLJ. MAIN UNCERTAINTIES REVOLVE AROUND
INFLUENCE OF PERSISTENT/PRIOR CONVECTION ON RETREAT OF WARM FRONT
OVER THIS REGION...AND RESULTING HINDRANCES TO DESTABILIZATION
THROUGH MUCH OF PERIOD.
..EDWARDS.. 04/01/2009
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