SWODY1
SPC AC 251959
DAY 1 CONVECTIVE OUTLOOK CORR 1
NWS STORM PREDICTION CENTER NORMAN OK
0259 PM CDT WED MAR 25 2009
VALID 252000Z - 261200Z
...THERE IS A SLGT RISK OF SVR TSTMS LATE THIS AFTN AND TONIGHT
ACROSS CNTRL/ERN TX THRU THE CNTRL GULF STATES...
CORRECTED FOR WRN EDGE OF HAIL/WIND PROBS IN TEXAS
...TEXAS THRU THE GULF STATES...
STRONG FORCING FOR UPWARD VERTICAL MOTION...ASSOCIATED WITH COUPLED
UPPER JET STREAKS...WILL CONTINUE TO DEVELOP EAST NORTHEAST OF THE
EDWARDS PLATEAU REGION OF TEXAS LATE THIS AFTERNOON AND EVENING. AS
THIS OCCURS...IT STILL APPEARS LIKELY THAT A BROAD LOW/MID-LEVEL
BAROCLINIC ZONE OVER CENTRAL/EASTERN TEXAS WILL PROVIDE THE FOCUS
FOR AN EVOLVING STORM CLUSTER...IN THE PRESENCE OF MODERATE
INSTABILITY ASSOCIATED WITH MOISTURE RETURN OFF THE GULF BENEATH
STEEP MID-LEVEL LAPSE RATES. DEEP LAYER SHEAR IS STRONG...AND
CLOCKWISE CURVED LOW-LEVEL HODOGRAPHS ARE BEGINNING TO ENLARGE
ACROSS THE UPPER TEXAS COASTAL PLAIN...AS SOUTHERLY 850 MB FLOW
BEGINS TO STRENGTHEN.
TORNADIC POTENTIAL REMAINS THE PRIMARY UNCERTAINTY...WITH THE BULK
OF THE ANTICIPATED CONVECTIVE DEVELOPMENT EXPECTED ALONG AND NORTH
OF A SURFACE BOUNDARY...NOW CURVING FROM A WEAKENING STORM CLUSTER
ACROSS SOUTHERN ALABAMA/MISSISSIPPI THROUGH SOUTHERN LOUISIANA INTO
SOUTH CENTRAL TEXAS. GIVEN THE LOWER AMPLITUDE NATURE OF THE
APPROACHING MID-LEVEL IMPULSE...A DRAMATIC RETREAT OF THE BOUNDARY
STILL APPEARS UNLIKELY. BUT...THE FRONT IS CURRENTLY LIFTING
NORTHWARD THROUGH THE COASTAL PLAIN...AND SOME ADDITIONAL NORTHWARD
ADVANCEMENT IS POSSIBLE AS A WEAK FRONTAL WAVE FORMS LATE THIS
AFTERNOON. FORCING IN THE IMMEDIATE VICINITY OF THE FRONT...JUST
AHEAD OF THE WAVE...IS EXPECTED TO BE THE PRIMARY FOCUS FOR ANY
TORNADIC SUPERCELLS.
EVEN AS UPSCALE CONVECTIVE GROWTH OCCURS THIS EVENING...A FOCUSED
TORNADO THREAT IS EXPECTED TO PERSIST...AND COULD INCREASE...NEAR
THE FRONTAL WAVE AS IT MIGRATES ACROSS CENTRAL LOUISIANA INTO NORTH
CENTRAL MISSISSIPPI...WHERE GUIDANCE INDICATES THAT THE SOUTHERLY
850 MB JET WILL STRENGTHEN TO AROUND 50 KTS. OTHERWISE...THE RISK
FOR DAMAGING WINDS WILL PROBABLY BECOME MORE PROMINENT THAN
HAIL...AS ACTIVITY ADVANCES EAST OF THE LOWER MISSISSIPPI VALLEY
INTO A PROGRESSIVELY WEAKER MID-LEVEL LAPSE RATE ENVIRONMENT.
..KERR.. 03/25/2009
.PREV DISCUSSION... /ISSUED 1126 AM CDT WED MAR 25 2009/
...SYNOPSIS...
WITHIN A BROAD UPPER TROUGH OVER THE ROCKIES AND PLAINS...THE
PRIMARY FEATURE OF INTEREST TODAY/TONIGHT WILL BE THE LOOSE PHASING
OF AN EWD MOVING SHORTWAVE TROUGH OVER NM WITH A SUBTROPICAL SPEED
MAX EJECTING EWD FROM NRN MEXICO TO CENTRAL TX. AT THE SURFACE...A
SLOW-MOVING COLD FRONT JUST S OF I-10 IN TX/LA WILL STALL AND BEGIN
TO LIFT SLOWLY NWD AS A WARM FRONT DURING THE DAY. A WAVE IS
FORECAST TO DEVELOP ALONG THE BOUNDARY THIS AFTERNOON/EVENING ACROSS
E TX...IN RESPONSE TO THE EJECTING SPEED MAXIMA AND PERHAPS FEEDBACK
FROM WIDESPREAD/INTENSE CONVECTION. THE WAVE IS THEN EXPECTED TO
MOVE ENEWD TO THE TN VALLEY LATE TONIGHT.
...TX/LA TODAY INTO MS/AL TONIGHT...
12Z SOUNDINGS REVEAL RICH LOW-LEVEL MOISTURE FROM S TX INTO SRN
LA...AND A PLUME OF 7-8 C/KM MID LEVEL LAPSE RATES OVER S AND W TX.
MOISTENING/DESTABILIZATION WILL OCCUR N OF THE SURFACE FRONT TODAY
OVER CENTRAL/E TX...WHERE CLUSTERS OF ELEVATED THUNDERSTORMS WILL
LIKELY DEVELOP BY EARLY AFTERNOON AND SPREAD EWD ALONG AND N OF THE
FRONT. THE ELEVATED STORMS N OF THE FRONT WILL BE CAPABLE OF
PRODUCING LARGE HAIL AND EVEN SOME DAMAGING WINDS GIVEN RELATIVELY
LARGE INSTABILITY ABOVE THE SHALLOW/COOL BOUNDARY LAYER. FARTHER S
ALONG THE FRONT...SURFACE-BASED SUPERCELLS WILL BE POSSIBLE. A FEED
OF 68-70 F BOUNDARY LAYER DEWPOINTS FROM THE S...STEEP MID LEVEL
LAPSE RATES...AND SURFACE HEATING WITHIN CLOUD BREAKS WILL SUPPORT
MLCAPE AOA 2000 J/KG FROM S CENTRAL INTO SE TX THIS AFTERNOON.
SHORT TERM MODEL FORECASTS DEPICT A RELATIVELY QUICK NWD RETREAT OF
THE WARM FRONT ACROSS TX/LA THIS AFTERNOON. SURFACE OBSERVATIONS
SUGGEST THE BOUNDARY HAS BEEN SLOW TO MOVE THROUGH LATE
MORNING...WHILE CLOUD COVER AND LATER DEVELOPMENT OF ELEVATED
CONVECTION MAY TEND TO REINFORCE THE BOUNDARY INTO THIS AFTERNOON.
FORECAST SOUNDINGS DO SHOW THE POTENTIAL FOR TORNADOES THIS
AFTERNOON INTO TONIGHT ALONG THE PATH OF THE SURFACE WAVE GIVEN
ROUGHLY 30 KT LOW-LEVEL FLOW AND STRONGLY CURVED LOW-LEVEL
HODOGRAPHS. STILL...THE BOUNDARY LOCATION...ALONG WITH THE
MAGNITUDE OF THE LOW-LEVEL FLOW RESPONSE AND RESULTANT LOW-LEVEL
SHEAR...CONTRIBUTE SOME UNCERTAINTY INTO THE EXPECTED CORRIDOR OF
GREATER SEVERE STORM/TORNADO THREAT. THE AREA FROM E TX ACROSS
LA/MS WILL CONTINUE TO BE MONITORED CLOSELY FOR AN INCREASE IN THE
TORNADO THREAT IN LATER UPDATES...THOUGH A SLIGHT RISK STILL APPEARS
APPROPRIATE BASED ON THE AFOREMENTIONED CONCERNS.
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