SPC AC 260559
DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1259 AM CDT SAT APR 26 2008
VALID 271200Z - 281200Z
...THERE IS A SLGT RISK OF SVR TSTMS DEEP S TX....WRN GULF COAST AND
MS DELTA REGION TO PORTIONS TN VALLEY REGION...
...SYNOPSIS...
PROGRESSIVE AND FAIRLY HIGHLY AMPLIFIED SHORTWAVE PATTERN IS FCST
WITHIN EWD-MOVING SYNOPTIC TROUGH OVER CENTRAL CONUS. MID-UPPER
LEVEL LOW NOW ANALYZED OVER MN IS EXPECTED TO BE FILLING AND
EJECTING NEWD INTO HUDSON BAY REGION BY 27/12Z...VERTICALLY STACKED
WITH SFC LOW BY THEN. TRAILING COLD FRONT -- NOW MOVING SEWD ACROSS
SWRN-ERN TX AND ERN AR...AND EWD OVER INDIANA AND LOWER MI -- SHOULD
OCCLUDE OVER GREAT LAKES/OH VALLEY AND REACH ERN NY...ERN PA...TO
OCCLUSION LOW JUST OFFSHORE TIDEWATER REGION BY BEGINNING OF PERIOD.
TRAILING COLD FRONTAL SEGMENT OVER CAROLINAS SHOULD ACT AS
PIEDMONT/DAMMING FRONT EARLY IN PERIOD...WEAKENING AND PROBABLY
RETREATING NWD AS WARM FRONT AFTER 28/00Z IN RESPONSE TO
STRENGTHENING SFC CYCLONE PASSING SW-NNW OF AREA.
MEANWHILE...SHORTWAVE TROUGH -- NOW EVIDENT IN MOISTURE CHANNEL
IMAGERY FROM NRN HIGH PLAINS NWD OVER SASK -- SHOULD DIG SEWD ACROSS
CENTRAL/NRN PLAINS DAY-1...THEN PIVOT EWD TO MID/UPPER MS VALLEY BY
28/12Z. ASSOCIATED SFC COLD FRONT WILL MOVE SEWD ACROSS MUCH OF SRN
PLAINS...REACHING SW TX AND ARKLATEX REGION BY 27/12Z. ALONG THAT
FRONT...CYCLOGENESIS IS EXPECTED EARLY IN PERIOD BETWEEN ARKLATEX
REGION AND MID MS VALLEY. SFC LOW SHOULD DEEPEN THROUGH MOST OF
PERIOD...LIFTING NEWD ACROSS KY AROUND 28/00Z AND OCCLUDING INVOF
WRN NY/NWRN PA BY 28/12Z. TRAILING COLD FRONT SHOULD REACH
SRN/CENTRAL APPALACHIANS AND EXTREME WRN FL PANHANDLE AROUND END OF
PERIOD.
...S TX...
SCATTERED TSTMS IN CLUSTERS ARE POSSIBLE ON EITHER SIDE OF
FRONT...WITH CONVECTION N OF FRONT POSING PRIMARY THREAT OF LARGE
HAIL. ACTIVITY MAY CONTINUE SWD/SEWD FROM LATE DAY-1 ACROSS
CENTRAL/S TX...AND/OR DEVELOP ANEW INVOF FRONT DURING AFTERNOON.
GIVEN PROGRESSIVE CHARACTER OF FRONTAL ZONE AND RELATIVE GEOMETRY OF
AMBIENT WINDS...EFFECTIVELY ANAFRONTAL REGIME IS FCST...ALTHOUGH
CONVECTION DEVELOPING ALONG FRONT MAY NOT BECOME ELEVATED RIGHT
AWAY. BY EARLY-MID AFTERNOON...PREFRONTAL AIR MASS ACROSS DEEP S TX
WILL BE CHARACTERIZED BY STG SFC HEATING...DEW POINTS UPPER 60S TO
LOW 70S F...BENEATH ELEVATED MIXED LAYER AIR THAT CONTAINS LAYERS OF
8-9 DEG C/KM LAPSE RATES. THEREFORE...WELL-MIXED SUBCLOUD LAYERS
AND LARGE BUOYANCY -- MLCAPES 2000-3000 J/KG -- ARE POSSIBLE. WEAK
LOW LEVEL WINDS SHOULD LIMIT HODOGRAPH SIZE...BUT MID-UPPER LEVEL
FLOW SHOULD BE STRONG ENOUGH TO AID IN STORM ORGANIZATION. DAMAGING
WIND AND LARGE HAIL ARE LIKELY WITH ANY SFC-BASED CONVECTION OVER
THIS AREA...BEFORE FROPA STABILIZES AIR MASS.
...MS DELTA REGION AND AL...
ONE OR TWO PRIMARY BANDS OF TSTMS ARE FCST TO DEVELOP INVOF SFC COLD
FRONT AND MOVE EWD ACROSS THIS REGION THROUGH AFTERNOON/EVENING
HOURS...WITH MARGINALLY SVR HAIL AND DAMAGING WIND BEING MAIN
CONCERNS. NRN PORTION OF THIS CONVECTION MAY RESULT FROM EWD
CONTINUATION OF EARLY PERIOD MCS IN NE TX/ARKLATEX
REGION...POTENTIALLY REINTENSIFYING AS IT MOVES INTO AIR MASS THAT
WILL BE DESTABILIZED DIURNALLY BY COMBINATION OF SFC HEATING AND
THETAE ADVECTION. MID 60S F SFC DEW POINT SHOULD COVER MOST OF MS
AHEAD OF COLD FRONT...AND MAY REACH PORTIONS NRN/WRN AL DUE TO MOIST
ADVECTION ASSOCIATED WITH SSWLY WARM SECTOR SFC FLOW. MEAN WIND
VECTOR WILL BE ALIGNED PARALLEL OR SLIGHTLY RIGHTWARD OF PRIMARY
BAND OF FORCING...INDICATING DOMINANT LINEAR MODE WITH SOME BOW/LEWP
DEVELOPMENT POSSIBLE. CONCENTRATION OF CONVECTION MAY YIELD SVR
COVERAGE WORTHY OF GREATER PROBABILITIES ACROSS SOME PORTIONS
MS/AL/LA...HOWEVER UNCERTAINTIES REGARDING INLAND EXTENT OF MOST
FAVORABLE HEATING/DESTABILIZATION PRECLUDE MORE THAN CATEGORICAL
CRITERIA NUMBERS ATTM. INFLOW-LAYER THETAE SHOULD DIMINISH BOTH
WITH NWD EXTENT THROUGH TN/KY...AND EWD EXTENT WITH TIME OVERNIGHT
ACROSS AL/GA...WITH SVR PROBABILITIES TRENDING DOWNWARD ACCORDINGLY.
...OH AND PORTIONS ADJACENT STATES...
ALTHOUGH INSTABILITY IS FCST TO BE VERY MEAGER OVER THIS
REGION...EXPECT STRENGTHENING WIND PROFILES AND DEEP-LAYER ASCENT
THROUGH LATE AFTERNOON AND EVENING...AS DEEPENING LOW LEVEL CYCLONE
APCHS. STRONGLY FORCED ARC OF LOW-TOPPED TSTMS MAY DEVELOP AND MOVE
RAPIDLY NEWD...WITH SOME GUSTS NEAR SVR LEVELS POSSIBLE. MOST
LIKELY PASSAGE OF THIS REGIME WILL BE AT SOMEWHAT UNFAVORABLE TIME
OF DAY AND NIGHT -- AFTER DIURNAL HEATING THAT WILL NOT BE VERY STG
ANYWAY BECAUSE OF PRECURSORY CLOUD COVER/PRECIP...AND SHALLOW/STABLE
LAYER OF POORLY MODIFIED CONTINENTAL AIR FROM PRIOR COLD FROPA MAY
STILL PERSIST NEAR SFC. SVR POTENTIAL APPEARS TOO CONDITIONAL FOR
CATEGORICAL OUTLOOK ATTM.
...CAROLINAS/NRN GA...
SCATTERED TSTMS MAY DEVELOP DURING AFTERNOON ALONG AND S OF FRONTAL
ZONE...WITH POTENTIAL FOR ISOLATED HAIL AND DAMAGING GUSTS. MAIN
CONVECTIVE MODE SHOULD BE MULTICELLULAR...GIVEN FCST OF RELATIVELY
WEAK LOW-MIDLEVEL WINDS IN MOST AREAS...THOUGH LOW LEVEL WINDS MAY
BECOME MORE FAVORABLE LATE AFTERNOON AND EARLY EVENING AS FIELD OF
STRONGEST ISALLOBARIC FORCING ASSOCIATED WITH FRONTAL-WAVE CYCLONE
PASSES CLOSEST TO REGION.
..EDWARDS.. 04/26/2008
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NOTE: THE NEXT DAY 2 OUTLOOK IS SCHEDULED BY 1730Z
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