SPC AC 261942
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0242 PM CDT THU MAR 26 2009
VALID 262000Z - 271200Z
...THERE IS A SLGT RISK OF SVR TSTMS THIS AFTN AND TONIGHT ACROSS
PARTS OF THE SERN PLAINS AND THE SRN PORTIONS OF THE GULF
STATES....
THERE IS LITTLE SUBSTANTIAL CHANGE TO PRIOR THINKING. TWO DISTINCT
AREAS OF STRONG MID/UPPER FORCING FOR UPWARD VERTICAL MOTION ARE
EXPECTED TO GENERALLY PROVIDE THE FOCUS FOR THE PRIMARY CONVECTIVE
DEVELOPMENT LATE THIS AFTERNOON AND EVENING.
...TEXAS COASTAL AREAS THRU SOUTHERN PORTIONS OF GULF STATES...
A DIVERGENT UPPER FLOW FIELD...ASSOCIATED WITH A SPEED MAXIMUM
EMBEDDED WITH A BELT OF WESTERLIES EMANATING FROM THE SUBTROPICAL
PACIFIC...IS CONTRIBUTING TO THE GRADUAL EVOLUTION OF A STRONG/
SEVERE STORM CLUSTER ACROSS THE MID/UPPER TEXAS COASTAL PLAIN. THIS
ACTIVITY IS EXPECTED TO CONTINUE EAST NORTHEASTWARD WITH UPPER
FORCING THROUGH THE REMAINDER OF THE PERIOD. IT IS POSSIBLE THAT A
SIGNIFICANT INCREASE IN ORGANIZATION MAY NOT OCCUR UNTIL LATER THIS
EVENING...WHEN CONVECTION BEGINS TO INTERACT WITH A STRENGTHENING
SOUTHWESTERLY 850 MB JET PROGGED ACROSS THE NORTH CENTRAL GULF OF
MEXICO INTO SOUTHERN LOUISIANA AND SOUTHWESTERN MISSISSIPPI. NEAR A
LINGERING CONVECTIVELY ENHANCED SURFACE BOUNDARY...THE AIR MASS
ACROSS THIS REGION IS SLOWLY RECOVERING IN THE WAKE OF THE WEAKENING
DOWNSTREAM CONVECTIVE SYSTEM. AND...CONDITIONS PROBABLY WILL BECOME
SUPPORTIVE OF ANOTHER DAMAGING WIND PRODUCING MESOSCALE CONVECTIVE
SYSTEM...WHICH COULD CONTINUE INTO SOUTHERN PORTIONS OF THE EASTERN
GULF STATES OVERNIGHT.
...PARTS OF THE S CNTRL PLAINS INTO THE OZARK PLATEAU...
STORMS BASED WITHIN A ELEVATED WARM ADVECTION REGIME...NORTH OF A
DEVELOPING SURFACE FRONT...ARE ALREADY ONGOING. THIS ACTIVITY
SHOULD PERSIST AND INCREASE LATE THIS AFTERNOON/TONIGHT...AS AN AREA
OF STRONGER MID/UPPER FORCING ASSOCIATED WITH A POLAR STREAK SPREADS
EAST NORTHEASTWARD OUT OF THE TEXAS PANHANDLE INTO THE OZARK
PLATEAU. A WINDOW OF OPPORTUNITY STILL APPEARS TO EXIST FOR
ISOLATED LATE AFTERNOON/EARLY EVENING SURFACE BASED STORM
DEVELOPMENT NEAR THE WARM FRONT/DRY LINE INTERSECTION ACROSS NORTH
CENTRAL TEXAS INTO SOUTH CENTRAL OKLAHOMA. IF THIS OCCURS...LATEST
SURFACE ANALYSIS SUGGESTS THAT BOUNDARY LAYER MOISTURE WILL BECOME
SUFFICIENT TO SUPPORT THE RISK FOR TORNADOES...IN AN ENVIRONMENT
OTHERWISE ALREADY SUPPORTIVE OF SUPERCELLS ALONG THE WARM FRONT
ACROSS THE RED RIVER VALLEY. AS THE PRIMARY SURFACE LOW MIGRATES
OUT OF THE HIGH PLAINS LATER THIS EVENING AND OVERNIGHT...SIMILAR
ADDITIONAL SURFACE OR NEAR SURFACE BASED SUPERCELL DEVELOPMENT MAY
CONTINUE ACROSS THE SAME GENERAL AREA ALONG THE RED RIVER.
..KERR.. 03/26/2009
.PREV DISCUSSION... /ISSUED 1130 AM CDT THU MAR 26 2009/
...SYNOPSIS...
LONGWAVE TROUGH IS EXPECTED TO PERSIST OVER THE CENTRAL STATES AS
UPSTREAM UPPER LOW OVER UT CONTINUES TO DIG SSEWD TOWARD THE
FOUR-CORNERS REGION THIS AFTERNOON AND INTO NM TONIGHT. LEAD UPPER
TROUGH OVER THE OH AND TN VALLEYS IS PROGRESSING NEWD AND IS
EXPECTED TO REACH THE LOWER GREAT LAKES TONIGHT.
CONVECTIVE OUTFLOW BOUNDARY FROM ONGOING THUNDERSTORMS OVER NWRN FL
AND ADJACENT GULF WATERS EXTENDS WWD OFF THE LA COAST AND ACROSS
SOUTH CENTRAL TX. THIS BOUNDARY IS EXPECTED TO LIFT SLOWLY NWD
ALONG THE LA COAST THIS AFTERNOON. THE TX PART OF THE BOUNDARY MAY
PERSIST AS NEW STORMS OVER THE WRN PART OF SOUTH CENTRAL TX SPREAD
EWD AND ASSOCIATED CLOUDS AND PRECIPITATION MAINTAIN A THERMAL
GRADIENT ALONG THE SRN EDGE OF THE MCS.
TO THE NORTH OF THE THIS BOUNDARY...A SURFACE LOW OVER NERN NM IS
EXPECTED TO DEVELOP ESEWD TOWARD THE TX/NM BORDER BY THIS EVENING
AND CONTINUE INTO CENTRAL TX BY THE END OF THE PERIOD. A WARM FRONT
EXTENDING FROM THE TX PANHANDLE SEWD INTO EAST CENTRAL TX IS
FORECAST TO BECOME BETTER DEFINED LATER THIS AFTERNOON NEAR THE RED
RIVER IN RESPONSE TO INCREASING DIABATIC HEATING AND VERTICAL
MIXING...WHILE A N/S DRY LINE GRADUALLY MOVES EWD INTO CENTRAL TX.
...SOUTH CENTRAL/SERN TX INTO SRN LA...
ELEVATED SEVERE STORMS OVER THE WRN PARTS OF SOUTH CENTRAL TX ARE
EXPECTED TO MOVE EWD THROUGH TONIGHT IN ASSOCIATION WITH UPPER LEVEL
JET STREAK MOVING EWD OUT OF NRN MEXICO. CONTINUED UPPER LEVEL
DIVERGENCE IN THE LEFT EXIT REGION OF THE JET STREAK COUPLED WITH
WEAK LOW LEVEL CONVERGENCE AND WARM ADVECTION WILL MAINTAIN A
FAVORABLE VERTICAL MOTION FIELD TO SUPPORT THE EWD MOVEMENT OF THE
MCS. VERY STEEP MID LEVEL LAPSE RATES AND INCREASING LOW LEVEL
MOISTURE WILL RESULT IN MUCAPE OF 2500-3500 J/KG...AND STRONG
EFFECTIVE BULK SHEAR OF 40-50 KT WILL MAINTAIN THREAT FOR SUPERCELL
STORMS WITH POTENTIAL TO PRODUCE VERY LARGE HAIL. THE ACTIVITY IS
FORECAST TO SPREAD EWD INTO SERN TX THIS AFTERNOON...AND CONTINUE
INTO SRN LA TONIGHT POSSIBLY REACHING FAR SRN MS LATE TONIGHT.
STORMS ARE EXPECTED TO GRADUALLY BECOME SURFACE BASED BY LATER THIS
AFTERNOON...WITH ADDITIONAL THREATS FOR DAMAGING WIND GUSTS AND A
FEW TORNADOES INCREASING DURING THE LATE AFTERNOON AND EVENING.
...ERN OK/AR/NERN TX/NRN LA/MS...
A STRONGER LOW LEVEL JET IS PREDICTED TO DEVELOP OVER NERN TX/SERN
OK THIS AFTERNOON IN RESPONSE AS STRONGER MID/UPPER LEVEL WINDS
DEVELOP ACROSS THE SRN ROCKIES. THIS WILL ENHANCE LOW LEVEL
CONVERGENCE/WARM ADVECTION ALONG AND NORTH OF THE DEVELOPING WARM
FRONT AS MOISTURE IS TRANSPORTED NWD. THUNDERSTORMS ARE EXPECTED TO
DEVELOP AND INCREASE IN COVERAGE...ESPECIALLY NORTH OF THE
FRONT...BY LATER THIS AFTERNOON AND EVENING. VERY FAVORABLE VEERING
WIND PROFILES WITH HEIGHT WILL CONTRIBUTE TO STRONG DEEP LAYER SHEAR
CONDUCIVE FOR SUPERCELL DEVELOPMENT GIVEN MUCAPE OF 1500-2500 J/KG.
THESE STORMS ARE EXPECTED TO SPREAD EWD DURING THE NIGHT TOWARD THE
MS RIVER....WITH STRONGEST STORMS CAPABLE OF PRODUCING VERY LARGE
HAIL...DAMAGING WINDS AND A FEW TORNADOES.
...SERN AL/SRN GA/NWRN FL...
BAND OF THUNDERSTORMS FRM SWRN GA INTO THE NRN GULF IS CONTINUING
EWD AS STORM INTENSITY OVER LAND GRADUALLY DIMINISHES. THIS
WEAKENING TREND IS LIKELY TO PERSIST AS THE OH/TN VALLEY SHORT WAVE
TROUGH LIFTS NEWD AWAY FROM THE AREA. AN ISOLATED SEVERE THREAT MAY
CONTINUE INTO THE AFTERNOON AS THE CONVECTION MOVES EWD.
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