SWODY1
SPC AC 290556
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1256 AM CDT TUE MAR 29 2011
VALID 291200Z - 301200Z
...THERE IS A SLGT RISK OF SVR TSTMS FROM THE LOWER MS VALLEY TO
SOUTH CENTRAL TX/LOWER RIO GRANDE VALLEY...
...SYNOPSIS...
SHORTWAVE TROUGH CURRENTLY APPROACHING CO PER WATER VAPOR IMAGERY IS
EXPECTED TO TURN EWD ACROSS THE CENTRAL PLAINS TODAY AND REACH THE
MID MS/LOWER OH VALLEYS BY 12Z WEDNESDAY. MEANWHILE...ZONAL FLOW
WILL PERSIST FROM THE SRN ROCKIES TO THE MIDDLE AND SRN ATLANTIC
COAST. A SHORTWAVE TROUGH...CURRENTLY MOVING ACROSS THE BAJA
REGION...IS EXPECTED TO REACH THE LOWER RIO GRANDE VALLEY BY 30/00Z
AND THE NWRN GULF COAST REGION BY THE END OF THE FORECAST PERIOD.
LOW LEVEL WINDS ACROSS E TX/LOWER MS VALLEY ARE EXPECTED TO BACK TO
SLY TODAY IN RESPONSE TO WEAK HEIGHT FALLS AS THE CO TROUGH
PROGRESSES EWD. THIS WILL ALLOW A WARM FRONT TO MOVE NWD INTO SRN
LA BY AFTERNOON WITH THE WRN EXTENT OF THIS BOUNDARY REACHING A
LITTLE FARTHER NWD INTO EAST CENTRAL TX. MEANWHILE...A COLD FRONT
WILL SHIFT S/SEWD THROUGH TX...INTERSECTING THE WARM FRONT OVER EAST
CENTRAL TX BY LATE AFTERNOON WITH THE TRAILING PORTION OF THIS FRONT
EXTENDING SWWD INTO SOUTH CENTRAL TX. THE COLD FRONT WILL PROGRESS
E/SEWD OFF THE TX COAST BY 12Z WEDNESDAY...WITH THE NEWD EXTENSION
STRETCHING INTO SRN MS AND NRN AL.
...ARKLATEX TO SERN TX AND EWD INTO LOWER MS VALLEY...
SLY LOW LEVEL WINDS DEVELOPING ACROSS THIS REGION WILL ALLOW
MOISTURE TO RETURN ACROSS THIS REGION WITH SURFACE DEWPOINTS IN THE
MID-UPPER 60S EXPECTED WITHIN THE WARM SECTOR. THIS COMBINED WITH
SURFACE HEATING BENEATH A PLUME OF STEEP MIDLEVEL LAPSE RATES /7.5-8
C PER KM/ WILL RESULT IN MODERATE INSTABILITY /MLCAPE 1500-2000 J
PER KG/ BY AFTERNOON.
ELEVATED TSTMS...SOME POSSIBLY PRODUCING HAIL...MAY BE ONGOING
ACROSS OK AT 12Z TODAY. LOW LEVEL WAA AND WEAK HEIGHT FALLS FROM
THE ARKLATEX TO SRN AR/WRN MS SHOULD SUPPORT ELEVATED TSTMS
DEVELOPING/SPREADING FROM THE SERN PLAINS THIS MORNING. WEAK
INSTABILITY WITH NWD EXTENT SHOULD LIMIT THE SEVERE WEATHER THREAT.
HOWEVER...STEEP MIDLEVEL LAPSE RATES AND EFFECTIVE BULK SHEAR AROUND
40 KT SUGGEST THE POTENTIAL FOR A FEW ORGANIZED STORMS...WITH HAIL
THE PRIMARY THREAT N OF THE RETREATING WARM FRONT.
MEANWHILE...SURFACE BASED TSTMS ARE EXPECTED TO DEVELOP THIS
AFTERNOON ALONG THE COLD FRONT IN E/SERN TX AND EWD ACROSS THE WARM
SECTOR IN LA TO SWRN MS. FORCING ATTENDANT TO LOW LEVEL WAA AND
LEAD SRN STREAM IMPULSE REACHING THIS REGION BY LATE AFTERNOON WILL
SUPPORT THIS ACTIVITY. MODERATE INSTABILITY AND EFFECTIVE BULK
SHEAR 40-50 KT WILL SUPPORT ORGANIZED /SUPERCELLULAR/ STORMS.
ALTHOUGH LOW LEVEL WINDS WILL TEND TO BE WEAK...VERTICAL VEERING
WINDS SUGGEST A POTENTIAL FOR TORNADOES FROM E TX INTO THE LOWER MS
VALLEY. IN ADDITION...STEEP MIDLEVEL LAPSE RATES WILL SUPPORT A
THREAT FOR HAIL...SOME POSSIBLY VERY LARGE...BUT OVERALL COVERAGE OF
SIGNIFICANT HAIL IS UNCERTAIN AT THIS TIME TO INCLUDE A 10 PERCENT
SIGNIFICANT HAIL CONTOUR.
STRONGER FORCING FOR ASCENT IS EXPECTED TO REACH THE NWRN GULF COAST
THIS EVENING AND SPREAD EWD TO THE CENTRAL GULF COAST BY 12Z
WEDNESDAY. THIS WILL INDUCE CYCLOGENESIS OVER SERN TX/SWRN LA WITH
THE LOW REACHING SERN LA/SERN MS REGION BY EARLY WEDNESDAY MORNING.
STRENGTHENING LLJ E OF THE LOW WILL ENHANCE LOW LEVEL SHEAR AND
SUPPORT AN OVERNIGHT TORNADO THREAT ACROSS SRN LA TO SERN MS/SWRN
AL.
...PARTS OF SOUTH CENTRAL TX/LOWER RIO GRANDE VALLEY...
MODELS SUGGEST ISOLATED TSTMS MAY DEVELOP BY LATE AFTERNOON/EARLY
EVENING ACROSS THE SRN EXTENT OF THE COLD FRONT AS IT MOVES INTO
SOUTH CENTRAL TX...ENCOUNTERING A MODERATELY UNSTABLE AIR MASS
/MLCAPE AROUND 2000 J PER KG/. THIS ACTIVITY WILL BE FURTHER
SUPPORTED BY FORCING WITH THE BAJA TROUGH AS IT MOVES ACROSS THIS
REGION. STORMS THAT DEVELOP IN THIS REGION WILL BE CAPABLE OF
PRODUCING LARGE HAIL...SOME VERY LARGE...GIVEN THE DEGREE OF
INSTABILITY...STEEP LAPSE RATES AND EFFECTIVE BULK SHEAR AROUND 50
KT FAVORABLE FOR SUPERCELLS. IN ADDITION...DAMAGING WINDS WILL BE A
THREAT. THIS ACTIVITY WILL SPREAD SWD IN THE EVENING AND THE
DIMINISH AS THE BOUNDARY LAYER STABILIZES WITH THE ONSET OF DIABATIC
COOLING.
..PETERS/COHEN.. 03/29/2011
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