SPC AC 251728
DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1228 PM CDT WED MAR 25 2009
VALID 261200Z - 271200Z
...THERE IS A SLGT RISK OF SVR TSTMS THU/THU NIGHT ACROSS PARTS OF
SE TX THRU THE CNTRL/ERN GULF STATES....
...THERE IS A SLGT RISK OF SVR TSTMS LATE THU AFTN/THU NIGHT ACROSS
PARTS OF THE S CNTRL PLAINS INTO THE OZARK PLATEAU....
...SYNOPSIS...
SUBSTANTIAL BLOCKING PERSISTS WITHIN THE LARGE-SCALE UPPER FLOW
PATTERN...AND LITTLE CHANGE TO THIS GENERAL REGIME IS EXPECTED
THROUGH THIS FORECAST PERIOD. BUT...WITHIN AN EMBEDDED BROAD UPPER
TROUGH ENCOMPASSING MUCH OF THE INTERIOR U.S...SIGNIFICANT
AMPLIFICATION IS PROGGED TO OCCUR...AS A STRONG MID/UPPER JET STREAK
AND ASSOCIATED SHORT WAVE TROUGH DIG ACROSS THE GREAT BASIN/SOUTHERN
ROCKIES REGION. MODELS INDICATE THAT THIS WILL SUPPORT SURFACE
CYCLOGENESIS TO THE LEE OF THE CENTRAL ROCKIES...THROUGH THE SOUTH
CENTRAL HIGH PLAINS...BY LATE THURSDAY/THURSDAY NIGHT.
AS THE UPPER IMPULSE GRADUALLY APPROACHES THE BASE OF THE LARGER
SCALE TROUGH TOWARD THE END OF THE PERIOD...GUIDANCE INDICATES THAT
IT WILL COME INCREASINGLY IN PHASE WITH A BRANCH OF STRONG UPPER
WESTERLIES EMANATING FROM THE LOWER LATITUDE EASTERN PACIFIC...AND
EXTENDING ACROSS THE NORTHERN MEXICAN PLATEAU THROUGH THE NORTHERN
GULF OF MEXICO. WITHIN THIS STREAM...ANOTHER IN A SERIES OF
EMBEDDED SPEED MAXIMA IS FORECAST TO NOSE NEAR OR JUST SOUTH OF
UPPER TEXAS COASTAL AREAS LATE THURSDAY AFTERNOON INTO THURSDAY
EVENING...BEFORE CONTINUING TOWARD THE EASTERN GULF STATES THROUGH
12Z FRIDAY. THIS WILL FOLLOW IN THE WAKE OF COUPLED
POLAR/SUBTROPICAL IMPULSE EXPECTED TO BE WEAKENING AND LIFTING AWAY
FROM THE OHIO/TENNESSEE VALLEYS EARLY IN THE PERIOD.
THE UPPER PATTERN WILL MAINTAIN AN INFLUX OF MOISTURE OFF THE GULF
OF MEXICO...BENEATH ELEVATED MIXED LAYER AIR ADVECTING EAST
NORTHEAST OF THE MEXICAN PLATEAU REGION. HOWEVER...THIS MAY MOSTLY
OCCUR ABOVE A LINGERING SURFACE BOUNDARY...EXPECTED TO ADVANCE INTO
OR ACROSS EASTERN GULF COASTAL AREAS EARLY IN THE PERIOD...WHILE
REMAINING QUASI-STATIONARY FROM NEAR THE CENTRAL GULF COAST INTO
SOUTH CENTRAL TEXAS.
...SOUTHEAST TEXAS THROUGH THE CENTRAL/EASTERN GULF STATES...
WEAK TO MODERATE INSTABILITY IN THE PRESENCE OF STRONG DEEP LAYER
SHEAR IS EXPECTED TO CONTRIBUTE TO THE MAINTENANCE OF A SEVERE
THREAT THROUGH THIS FORECAST PERIOD AND BEYOND. FOR THURSDAY/
THURSDAY NIGHT...THE AFOREMENTIONED QUASI-STATIONARY SURFACE FRONT
SEEMS LIKELY TO PROVIDE THE FOCUS FOR THE PRIMARY CONVECTIVE
DEVELOPMENT.
IT CURRENTLY APPEARS LIKELY THAT A CLUSTER OF STORMS WILL BE ONGOING
ACROSS ALABAMA/SOUTHEAST MISSISSIPPI AND SOUTHERN LOUISIANA AT THE
OUTSET OF THE PERIOD. PROPAGATING INTO A LESS FAVORABLE
ENVIRONMENT...IT SEEMS PROBABLE THAT ACTIVITY WILL BE IN THE PROCESS
OF WEAKENING...IN THE WAKE OF DEPARTING UPPER FORCING. BUT...THE
RISK FOR POTENTIALLY DAMAGING WIND GUSTS...PERHAPS AN ISOLATED
TORNADO...MAY PERSIST UNTIL ACTIVITY DISSIPATES OR DEVELOPS OFFSHORE
LATER IN THE MORNING.
THEREAFTER...DAYTIME DESTABILIZATION COUPLED WITH STRENGTHENING LIFT
AHEAD OF THE APPROACHING JET STREAK IS EXPECTED TO SUPPORT RENEWED
STORM DEVELOPMENT ALONG THE BOUNDARY ACROSS PARTS OF SOUTHEAST
TEXAS. ACTIVITY MAY INITIATE AS SUPERCELLS...WITH THE RISK FOR
LARGE HAIL/DAMAGING WINDS...AND THE POTENTIAL FOR TORNADOES MAY
INCREASE DURING THE EVENING INTO THE OVERNIGHT HOURS ...AS A MODEST
SOUTHWESTERLY LOW-LEVEL JET FORMS AS ACTIVITY SPREADS EASTWARD
ACROSS THE CENTRAL GULF COAST/LOWER MISSISSIPPI VALLEY REGION.
BUT...LARGE-SCALE FORCING SEEMS FAVORABLE FOR THE EVOLUTION OF
ANOTHER MESOSCALE CONVECTIVE SYSTEM...WITH DAMAGING WINDS BECOMING
THE MORE PROMINENT THREAT...WHICH MAY SPREAD THROUGH SOUTHERN
ALABAMA BY 12Z FRIDAY.
...SOUTHERN PLAINS INTO THE OZARK PLATEAU...
WARMING MID-LEVELS AHEAD OF STRONG DIGGING UPSTREAM TROUGH WILL
CONTRIBUTE TO INCREASED INHIBITION ACROSS MUCH OF THE SOUTHERN
PLAINS...PARTICULARLY SOUTH OF THE WARM FRONT FORMING NEAR THE RED
RIVER...TO THE EAST OF THE DEVELOPING SURFACE CYCLONE. IT IS
POSSIBLE THAT ISOLATED CONVECTIVE DEVELOPMENT...IN AN ENVIRONMENT
FAVORABLE FOR SUPERCELLS...MAY OCCUR NEAR THE DRY LINE/WARM FRONT
INTERSECTION ACROSS PARTS OF NORTH CENTRAL TEXAS/SOUTH CENTRAL
OKLAHOMA LATE THURSDAY AFTERNOON. BUT...IT APPEARS MORE PROBABLE
THAT THE PRIMARY CONVECTIVE DEVELOPMENT WILL OCCUR AFTER DARK...
BASED IN AN ELEVATED WARM ADVECTION REGIME TO THE NORTH OF THE
FRONT...ACROSS PARTS OF CENTRAL/EASTERN OKLAHOMA INTO ARKANSAS.
SHEAR SHOULD STILL BE FAVORABLE FOR SUBSTANTIAL UPDRAFT ROTATION
...WHICH WILL ENHANCE THE RISK FOR LARGE HAIL IN THE MOST VIGOROUS
STORMS.
..KERR.. 03/25/2009
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NOTE: THE NEXT DAY 2 OUTLOOK IS SCHEDULED BY 0600Z
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