SPC AC 270500
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1200 AM CDT SUN MAR 27 2011
VALID 271200Z - 281200Z
...THERE IS A SLGT RISK OF SVR TSTMS PORTIONS SRN GA/AL REGION...
...SYNOPSIS...
SPLIT-FLOW PATTERN FCST TO PERSIST OVER N-CENTRAL NORTH AMERICA.
BROAD/QUASI-ZONAL FETCH OF SRN-STREAM WLYS WILL EXTEND FROM NERN PAC
ACROSS GREAT BASIN...CENTRAL/SRN PLAINS...LOWER-MID MS VALLEY AND
MIDDLE-SRN ATLANTIC COAST REGION...WITH SEVERAL EMBEDDED SHORTWAVES.
LEADING/MINOR PERTURBATION -- INITIALLY ANALYZED OVER OH VALLEY --
WILL BECOME VERY WEAK AND MOVE OFFSHORE BEFORE START OF PERIOD.
CLOSELY TRAILING TROUGH -- EVIDENT OVER PORTIONS IL AND LOWER OH
VALLEY -- LIKEWISE IS FCST TO WEAKEN AMIDST CONFLUENT MID-UPPER
WINDS...MOVING OFFSHORE DELMARVA/MID-ATLANTIC REGION AROUND 27/18Z.
AT SFC...FRONTAL-WAVE LOW ASSOCIATED WITH LEADING SHORTWAVE TROUGHS
WILL DEVELOP OFFSHORE NC AROUND 27/12Z AND MOVE EWD OVER
ATLANTIC...WHILE TRAILING LOW NOW OVER CENTRAL AL WEAKENS.
ACCOMPANYING BAROCLINIC ZONE WILL SAG SWD ACROSS GA/AL/MS...LIKELY
AIDED BY ONGOING CONVECTION. BY 28/00Z...FRONT SHOULD BE
DECELERATING...AND SHOULD BECOME QUASISTATIONARY OVER SRN PORTIONS
GA/AL AND SERN LA BY END OF PERIOD.
FARTHER NW...WEAKENING UPPER LOW IS FCST TO CONTINUE MOVING INLAND
WA/SWRN BC...WHILE SRN LOBE OF ACCOMPANYING SHORTWAVE TROUGH OVER
ORE BREAKS ESEWD OVER GREAT BASIN BY 27/12Z. THIS PERTURBATION
SHOULD REACH PORTIONS KS/OK BY 28/00Z...AND KY NEAR END OF PERIOD.
...SRN GA/AL REGION...
SVR PROBABILITIES AND CONVECTIVE COVERAGE EACH SHOULD BE MAXIMIZED
DIURNALLY INVOF BAROCLINIC ZONE...WHERE AFTERNOON MLCAPE 1000-1500
J/KG MAY DEVELOP IN AREAS OF MID-UPPER 60S F SFC DEW POINTS. STG
WINDS ALOFT -- E.G. 50-60 KT AT 500 MB AND 90-110 KT AT 250 MB --
WILL MAINTAIN FAVORABLE DEEP-LAYER SHEAR AND STORM-RELATIVE WINDS IN
MID-UPPER LEVELS. THIS SHOULD CONTRIBUTE TO POTENTIAL FOR ORGANIZED
CONVECTION...DESPITE IMPEDIMENTS TO CONVERGENCE AND LOW-LEVEL
STORM-RELATIVE WINDS IMPARTED BY VEERED/WEAK WINDS AT SFC.
FCST HODOGRAPHS ARE LOOSELY LINER IN SHAPE...AMIDST 40-50 KT
EFFECTIVE SHEAR MAGNITUDES...INDICATING POTENTIAL FOR SPLITTING
STORMS WITH LARGE HAIL AND DAMAGING GUSTS BEING POSSIBLE. TORNADO
POTENTIAL CANNOT BE RULED OUT...BUT AMBIENT HODOGRAPHS ARE SMALL
ENOUGH THAT IT WILL DEPEND CONDITIONALLY ON STORM-SCALE PROCESSES
AND MESOBETA SCALE BOUNDARY INTERACTIONS. SVR POTENTIAL SHOULD
DIMINISH MARKEDLY AFTER DARK...GIVEN LACK OF SUBSTANTIAL MID-UPPER
SUPPORT AND BOUNDARY-LAYER STABILIZATION REMOVING SFC-BASED PARCELS
FROM EFFECTIVE INFLOW LAYER.
....ARKLATEX/LOWER MS VALLEY...
APCH OF MID-UPPER WAVE WILL ENHANCE ALREADY FAVORABLE DEEP-LAYER
SHEAR...AS WELL AS LOW-LEVEL WAA/ISENTROPIC LIFT...N OF SFC FRONT
ACROSS THIS REGION. REMAINS OF ELEVATED MIXED-LAYER AIR WILL
CONTRIBUTE TO STEEP MIDLEVEL LAPSE RATES AND ENHANCED BUOYANCY WHERE
PARCELS CAN REACH LFC. ETA-KF FCST SOUNDINGS...AS WELL AS RUC
SOUNDINGS EXTENDING INTO EARLY/MID AFTERNOON...REASONABLY FCST
ELEVATED MUCAPE OF AT LEAST 1500 J/KG OVER PARTS OF THIS
REGION...WITH 40-50 KT EFFECTIVE SHEAR MAGNITUDES. MAIN CONCERN
WOULD BE LARGE HAIL.
...MID-UPPER TX COASTAL PLAIN...
VERY CONDITIONAL AND PERHAPS SFC-BASED SVR POTENTIAL IS APPARENT IN
DEVELOPMENT OF CONVECTIVE PRECIP BY WRF-ARW AND SPECTRAL MEMBERS OF
SREF ALONG MID/UPPER TX COAST...INVOF FRONT. HOWEVER...CHARACTER OF
ANTECEDENT EML...WHICH IS FCST TO CHANGE LITTLE AS MID-UPPER WAVE
PASSES WELL N OF AREA...SHOULD RESULT IN UNFAVORABLE CAP STRENGTH
FOR MOST AND PERHAPS ALL AFTERNOON. UNCONDITIONAL SVR PROBABILITIES
DO NOT APPEAR JUSTIFIED FOR THIS REGION ATTM...THOUGH ISOLATED TSTM
DEVELOPMENT CANNOT BE RULED OUT COMPLETELY.
..EDWARDS/DEAN.. 03/27/2011
CLICK TO GET WUUS01 PTSDY1 PRODUCT
NOTE: THE NEXT DAY 1 OUTLOOK IS SCHEDULED BY 1300Z
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