SWODY2
SPC AC 121730
DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1230 PM CDT TUE AUG 12 2008
VALID 131200Z - 141200Z
...THERE IS A SLGT RISK OF SVR TSTMS PORTIONS CENTRAL HIGH PLAINS...
...THERE IS A SLGT RISK OF SVR TSTMS PORTIONS GA AND CAROLINAS...
...SYNOPSIS...
UPPER AIR PATTERN THIS PERIOD IS FCST TO FEATURE SLOW-MOVING UPPER
LOWS OVER SASK AND QUE...RIDGING FROM MN NWD INTO QUASISTATIONARY
HIGH OVER COASTAL MB...AND BROAD FETCH OF NW FLOW FROM NRN ROCKIES
TO GULF COAST STATES. AS NRN STREAM SHORTWAVE TROUGH AMPLIFIES
ACROSS NW TERRITORIES...SASK LOW WILL ESCAPE SEWD FROM PRESENT
POSITIVELY-TILTED REX CONFIGURATION OVER CENTRAL CANADA...AND BEGIN
TO DIG SEWD TOWARD ND. THIS PROCESS...IN TURN...SHOULD TIGHTEN
HEIGHT GRADIENTS OVER NRN PLAINS...FOSTERING SEWD EJECTION OF
SEPARATE/OPEN-WAVE SHORTWAVE TROUGH FROM NRN ROCKIES INTO DIFLUENT
FLOW OVER NEB PANHANDLE BY AROUND 14/00Z.
MEANWHILE...WEAK/LOW-AMPLITUDE PERTURBATIONS WILL REVOLVE AROUND
LARGE QUE CYCLONE...AHEAD OF STRONGER SHORTWAVE FCST TO DIG SWD TO
LS AND LH BY END OF PERIOD. SRN STREAM SHORTWAVE TROUGH -- NOW
EVIDENT IN MOISTURE CHANNEL IMAGERY AND VWP/PROFILER DATA OVER AR --
SHOULD PIVOT EWD THROUGH MEAN ERN TROUGH POSITION...THEN MOVE ACROSS
AND OFFSHORE CAROLINAS EARLY THIS PERIOD.
AT SFC...LOW NOW OVER ARKLATEX REGION IS EXPECTED TO MOVE EWD WITHIN
BROAD/DIFFUSE FRONTAL ZONE...FROM GA EWD ACROSS ERN SC AND SERN NC
BEFORE 13/00Z. TIMING DIFFERENCES ALOFT WITH PARENT SHORTWAVE
TROUGH -- EVIDENT IN FASTER SPECTRAL AND SLOWER WRF -- ARE EVEN MORE
PRONOUNCED AT SFC. WITH SPECTRAL MORE STRONGLY INFLUENCED BY
CONVECTIVE FEEDBACK...AND ECMWF/WRF AGREEMENT MORE IN STEP WITH SREF
CONSENSUS...WILL FCST LOW IN ILM-MHX AREA BY 14/00Z. FARTHER
W...WEAK LEE-SIDE LOW SHOULD DEVELOP ACROSS CENTRAL HIGH PLAINS
VICINITY NERN CO/SWRN NEB...WITH TROUGHING EXTENDING NEWD ACROSS
SANDHILLS REGION..DURING 13/18-14/00Z TIME FRAME.
...CENTRAL HIGH PLAINS...
OUTLOOK REPRESENTS SPATIAL JUXTAPOSITION OF TWO TEMPORALLY
DISCONNECTED SCENARIOS...
1. AFTERNOON SVR TSTM DEVELOPMENT NEAR OR NE OF WEAK SFC LOW INVOF
SFC TROUGH. STG SFC HEATING...STEEP MIDLEVEL LAPSE RATES AND SFC
DEW POINTS IN UPPER 50S TO 60S F WILL CONTRIBUTE FAVORABLE BUOYANCY
AND WEAKENING CINH BY MID-LATE AFTERNOON. FCST SOUNDINGS SUGGEST
STG VEERING WITH HEIGHT BUT WEAK LOW LEVEL WINDS...SUPPORTING
POTENTIAL FOR SOME UPSCALE GROWTH AND FORWARD PROPAGATION OF EARLY
CONVECTION SEWD TO SSEWD ACROSS CENTRAL HIGH PLAINS. MAIN CONCERNS
WILL BE LARGE HAIL AND DAMAGING GUSTS.
2. LATE-PERIOD TSTM FORMATION OVER SERN WY AND NEB PANHANDLE
REGION...IN REGIME OF ELEVATED LOW LEVEL WAA AND INCREASING
MID-UPPER ASCENT AHEAD OF APCHG NRN ROCKIES SHORTWAVE TROUGH.
ELEVATED MUCAPES APCHG 2000 J/KG ARE POSSIBLE WITH LARGE HAIL BEING
MAIN CONCERN. HOWEVER...FCST SOUNDINGS BETWEEN 14/06Z AND 14/12Z
ACROSS THIS REGION SUGGEST ENOUGH BOUNDARY LAYER THETAE TO KEEP
AFFECTIVE LIFTED PARCELS AT OR VERY NEAR SFC...SO CONVECTION MAY NOT
NECESSARILY BE ELEVATED. THEREFORE...ANY UPSCALE ORGANIZATION OF
COMPLEX MAY SUPPORT DAMAGING WIND POTENTIAL AS WELL.
...SERN CONUS...
VERY MOIST AND WEAKLY CAPPED AIR MASS WILL BE IN PLACE TO SUPPORT
SFC-BASED INFLOW PARCELS RIGHT FROM START OF PERIOD OVER GA...EWD
ACROSS PORTIONS SC TO SRN NC BEFORE 00Z. NEAR SFC LOW...AND TO ITS
E INVOF FRONTAL ZONE...BACKED LOW LEVEL WINDS WILL CONTRIBUTE TO
VERY LARGE HODOGRAPHS -- WITH 0-1 KM SRH VALUES POTENTIALLY
EXCEEDING 400 J/KG IN SOME AREAS WITH TSTMS ROOTED AT SFC. MAIN
CONCERN WILL BE SMALL/TORNADIC SUPERCELLS...PERHAPS EMBEDDED WITHIN
BROADER AREAS OF CONVECTION. ANY AREAS OF BKN/SCTD CLOUDS AND
RELATED ENHANCEMENTS TO SFC HEATING...WHICH WOULD DEEPEN BUOYANT
PROFILE AND ENLARGE CAPE CONSIDERABLY GIVEN NEARLY MOIST-ADIABATIC
LAPSE RATES ALOFT. ISOLATED DAMAGING WIND ALSO MAY OCCUR. LIMITING
FACTORS WILL INCLUDE WEAKNESS OF HODOGRAPH IN MIDLEVELS -- RESULTING
IN LACK OF ROBUST EFFECTIVE/DEEP-LAYER SHEAR...AND RESTRICTIONS ON
BUOYANCY IMPOSED BY WEAK LAPSE RATES AND CLOUD COVER/PRECIP.
THEREFORE...WILL KEEP OUTLOOK PROBABILITIES WITHIN CATEGORICAL SLGT
RISK CRITERIA ATTM.
..EDWARDS.. 08/12/2008
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