SPC AC 241959
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0259 PM CDT FRI APR 24 2009
VALID 242000Z - 251200Z
...THERE IS A SLGT RISK OF SVR TSTMS ACROSS PARTS OF THE CNTRL
PLAINS AND UPPER MIDWEST...
...THERE IS A SLGT RISK OF SVR TSTMS ACROSS PARTS OF TEXAS...
...UPPER MIDWEST...
A MINOR CHANGE TO THE SLIGHT RISK AREA IN THE UPPER MIDWEST IS TO
MOVE THE SLIGHT RISK CORRIDOR TO THE NORTHWEST. THE FRONT HAS BEEN
SLOWER TO ADVANCE SEWD ACROSS SE MN PROBABLY DUE TO A SFC LOW IN
PLACE ACROSS THE REGION. ADJUSTED THE POSITION OF THE SLIGHT RISK TO
BETTER CORRESPOND TO SFC ANALYSIS FEATURES AND SHORT-RANGE MODEL
FORECASTS.
...TEXAS...
THE SLIGHT RISK AREA HAS BEEN NARROWED AND IS ORIENTED ALONG A
LOW-LEVEL JET WHICH WILL PROVIDE STRONGER LOW-LEVEL FLOW FOR AN
ISOLATED WIND DAMAGE OR TORNADO POTENTIAL WITH NEW CELLS THAT
INITIATE LATE THIS AFTERNOON. ALTHOUGH THE 18Z RUC IS SLIGHTLY
FARTHER EAST WITH CONVECTIVE DEVELOPMENT LATE THIS AFTERNOON THAN
EITHER THE HIGH RES ARW AND NMM MODELS...BOTH AGREE THAT THE
GREATEST SFC-BASED CONVECTIVE POTENTIAL EXISTS IN THIS NARROW
CORRIDOR ACROSS EAST TX. A FEW STRONG THUNDERSTORMS WITH A MARGINAL
SEVERE POTENTIAL MAY ALSO MOVE NWD INTO ERN OK EARLY THIS EVENING.
..BROYLES.. 04/24/2009
.PREV DISCUSSION... /ISSUED 1107 AM CDT FRI APR 24 2009/
...SYNOPSIS...
MAJOR PATTERN CHANGE UNDERWAY AS TROUGH CONTINUES TO DEVELOP WRN
US...AND RIDGE BECOMES MORE DOMINATE IN THE E. COLD FRONT CURRENTLY
WRN LS SWWD TO ERN NE AND THEN WWD INTO NERN CO WILL BE FOCUS FOR
THUNDERSTORM INITIATION BY LATER THIS AFTERNOON.
WHILE A STRONG UPPER COLD LOW DROPS SEWD THRU CENTRAL CA TODAY A
MUCH WEAKER SRN BRANCH TROUGH WILL BE MOVING SLOWLY EWD CENTRAL TX.
40-50KT LLJ AHEAD OF THE COLD FRONT FROM TX TO THE UPPER GREAT LAKES
IS TRANSPORTING INCREASING GULF MOISTURE NWD CENTRAL PORTION OF THE
CONUS THROUGH THE PERIOD.
...CENTRAL/ERN TX...
THE WEAK UPPER TROUGH/VORT CENTER AT 15Z LOCATED VICINITY ABI WILL
DRIFT EWD INTO NERN TX BY THIS EVENING. SUBSTANTIAL INCREASE IN LOW
LEVEL MOISTURE OCCURRED OVERNIGHT ACROSS CENTRAL/ERN TX WHICH
COUPLED WITH THE RELATIVELY COLD/STEEP MID LEVEL LAPSE RATES
ASSOCIATED WITH THE UPPER TROUGH HAS PUT IN PLACE A CONDITIONALLY
QUITE UNSTABLE AIR MASS WITH MLCAPES AOA 2000 J/KG BY EARLY THIS
AFTERNOON. THINNING OF MORNING CLOUDINESS WILL BE SUFFICIENT FOR
HEATING TO GENERALLY ELIMINATE CURRENT CINH. THUNDERSTORMS SHOULD
INCREASE IN NUMBER AND INTENSITY BY MID DAY CENTRAL TX AND SPREAD
E/SEWD ACROSS THE UNSTABLE WARM SECTOR THRU THE EVENING. WITH
EXPECTED INSTABILITY AND STEEP MID LEVEL LAPSE RATES...LARGE HAIL
WILL BE A CONCERN WITH STRONGER STORMS. THERE WILL BE ADDITIONALLY
SUFFICIENT SHEAR AHEAD OF UPPER TROUGH FOR ISOLATED SUPERCELL
DEVELOPMENT. THIS WILL THEN SUPPORT THREAT OF AT LEAST AN ISOLATED
TORNADO THREAT ALONG WITH DAMAGING WINDS.
...NRN WI TO LWR MO VLY...
TSTMS SHOULD FORM INVOF COLD FRONT LATE THIS AFTN AND THIS EVE FROM
NRN WI SW INTO NRN KS AS SFC HEATING AND WEAK DPVA DESTABILIZE
REGION. THE STORMS LIKELY WILL FIRST FORM IN SMALL CLUSTERS RELATED
TO THE PRESENCE OF WEAK SFC WAVES. THEY SHOULD...HOWEVER...MERGE
INTO A MORE OR LESS CONTINUOUS BAND BY EARLY EVE. GIVEN LINEAR
FORCING OF FRONT...DECENT POTENTIAL FOR COLD DOWN DRAFT
DEVELOPMENT...AND LARGELY UNIDIRECTIONAL DEEP WSW FLOW PARALLEL TO
BOUNDARY...A QUASI-LINEAR MODE SHOULD DOMINATE. AMPLE /40+ KT/ DEEP
SHEAR WILL NEVERTHELESS BE PRESENT TO SUPPORT MID LVL STORM ROTATION
AND THE POTENTIAL FOR EMBEDDED SUSTAINED STORMS/SUPERCELLS. THESE
COULD YIELD BOTH SVR HAIL AND WIND. A FEW SIGNIFICANT SVR HAIL
EVENTS COULD OCCUR AS COMBINATION OF NEAR 60F SFC DEW POINTS AND
RELATIVELY COOL MID LEVEL TEMPERATURES BOOST SBCAPE TO 1500-2000
J/KG.
STORM COVERAGE EXPECTED TO REMAIN MORE ISOLD WITH SW EXTENT ALONG
FRONT...WHERE STRONGER CIN WILL EXIST ALONG WITH GREATER
HEATING/STEEPER LOW LVL LAPSE RATES. THE SVR THREAT SHOULD DIMINISH
AFTER ABOUT 06Z AS BOUNDARY LAYER STABILIZES AND AS PREFRONTAL LLJ
BECOMES MORE PARALLEL TO FRONT.
..CAROLINAS...
WDLY SCTD TSTMS MAY FORM THIS AFTN ALONG GPS/SATELLITE-INDICATED PW
AXIS OVER THE GA/SC/SRN NC PIEDMONT/CSTL PLN. DEVELOPMENT ALSO MAY
BE FOSTERED OVER THE WRN CAROLINAS BY HIGHER TERRAIN AND CLOSER
PROXIMITY TO STEEPER LAPSE RATES ALOFT /ACCAS IN VISIBLE IMAGERY/.
ALTHOUGH DEEP SHEAR WILL BE MEAGER CLOSE TO UPR RIDGE...MLCAPE OF
1500-2500 J/KG ATOP FAIRLY DEEP WELL-MIXED/SUB CLOUD LAYER COULD
YIELD MULTICELLS WITH LOCALLY STRONG/SVR WIND GUSTS AND ISOLD
MARGINALLY SVR HAIL.
...LWR GRT LKS...
PERSISTENT WAA ATOP SLOWLY RECEDING MODIFIED POLAR AIR MASS MAY
SUPPORT ADDITIONAL ROUNDS OF SLIGHTLY ELEVATED STORMS LATER TODAY
THROUGH THIS EVE OVER NERN OH/NWRN PA AND WRN NY. ALTHOUGH DEGREE
OF ELEVATED INSTABILITY INITIALLY WILL BE QUITE LIMITED...ARRIVAL OF
MORE SUBSTANTIAL PW POCKET NOW OVER MO/IL MAY BOOST MUCAPE TO NEAR
1500 J/KG. GIVEN PRESENCE OF SUSTAINED UPDRAFTS AND MID LEVEL LAPSE
RATES IN EXCESS OF 7C/KM...SETUP COULD SUPPORT A CONDITIONAL RISK
FOR SVR HAIL GIVEN 40 KT CLOUD LAYER SHEAR ACROSS REGION.
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NOTE: THE NEXT DAY 1 OUTLOOK IS SCHEDULED BY 0100Z
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