SWODY1
SPC AC 130527
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1127 PM CST THU FEB 12 2009
VALID 131200Z - 141200Z
...NO SVR TSTM AREAS FORECAST...
...SYNOPSIS...
IN MID-UPPER LEVELS...NEARLY ZONAL FLOW REGIME FCST TO PREVAIL
ACROSS MOST OF CONUS...DOWNSTREAM FROM DEEP-LAYER CYCLONE NOW
LOCATED OFFSHORE PACIFIC NW. SUBSTANTIAL PORTION OF THIS CYCLONE IS
EXPECTED TO DIG SEWD OVER NWRN CA THROUGH 14/06Z...THEN EVOLVE INTO
NEGATIVELY TILTED OPEN-WAVE TROUGH WITH STRONGLY DIFLUENT UPPER WIND
FIELDS FROM NRN CA SEWD TO 4-CORNERS REGION. DOWNSTREAM
PERTURBATION -- NOW EVIDENT IN MOISTURE CHANNEL IMAGERY MOVING ENEWD
FROM 4-CORNERS AREA TO CENTRAL/SRN ROCKIES -- WILL MOVE ENEWD AND
GRADUALLY DEAMPLIFY. THIS FEATURE SHOULD MOVE OVER NRN KS AND NEB
DURING AFTERNOON...WEAKENING FURTHER AND PHASING WITH NRN STREAM
TROUGH OVER UPPER GREAT LAKES BY END OF PERIOD.
AT SFC...LEE-SIDE CYCLONE NOW DEVELOPING OVER NERN NM IS FCST TO
STRENGTHEN THROUGH FIRST HALF OF PERIOD...EJECTING ENEWD ACROSS
S-CENTRAL PLAINS AHEAD OF MID-UPPER PERTURBATION. BY ABOUT
24/00Z...LOW SHOULD MOVE OVER WRN OZARKS...THEN EWD INVOF WRN KY BY
END OF PERIOD. TRAILING COLD FRONT SHOULD MOVE SEWD ACROSS MOST OF
AR/OK/TX DURING PERIOD...REACHING FROM LOW TO MIDDLE-UPPER TX
COASTAL PLAIN AND S-CENTRAL TX BY 14/12Z. MEANWHILE...RESIDUAL
FRONTAL ZONE NOW ANALYZED ACROSS N-CENTRAL/NWRN GULF WILL CONTINUE
TO RETREAT NWD AS WARM FRONT THROUGH PERIOD...DEMARCATING
WELL-MODIFIED MARINE AIR TO ITS S FROM SHALLOW LAYER OF RELATIVELY
COOL/STABLE CONTINENTAL TRAJECTORIES TO ITS N.
...MS DELTA...DEEP SOUTH...
TSTM COVERAGE N OF MARINE FRONT IS FCST TO INCREASE THROUGHOUT EARLY
PART OF PERIOD. LOW LEVEL WAA AND MOISTURE TRANSPORT REGIME ATOP
FRONTAL LAYER SHOULD BOOST THETAE ENOUGH TO SUPPORT ELEVATED MUCAPE
500-800 J/KG NEAR COAST...DECREASING WITH NWD EXTENT DURING MORNING.
PARCELS WILL BE LIFTED ISENTROPICALLY TO LFC...AMIDST EFFECTIVE
SHEAR MAGNITUDES OCCASIONALLY REACHING 35-45 KT RANGE -- STORM DEPTH
DEPENDENT. ISOLATED HAIL NEAR SVR LEVELS MAY OCCUR WITH MOST
INTENSE/PERSISTENT CELLS IN THIS REGIME.
COMBINATION OF SFC HEATING -- AWAY FROM AREAS OF PRE-EXISTING
CLOUDS/PRECIP -- AND WAA ASSOCIATED WITH MARINE FRONTAL ZONE -- MAY
RESULT IN SFC-BASED LIFTED PARCELS OVER COASTAL AREAS OF MS AND
PORTIONS SERN LA DURING AFTERNOON AND EARLY EVENING. ALTHOUGH NO
SIGNIFICANT UPPER PERTURBATIONS ARE EXPECTED TO AFFECT THIS AREA
DIRECTLY...SUFFICIENTLY TIGHT HEIGHT GRADIENT WILL EXIST TO SUPPORT
STG MID-UPPER WINDS AND FAVORABLE DEEP-LAYER VERTICAL SHEAR. LOW
LEVEL WINDS ARE FCST TO VEER STRONGLY WITH HEIGHT ALONG AND N OF
MARINE FRONT...THOUGH BULK OF SFC-BASED EFFECTIVE LIFTED PARCELS
WILL BE S OF FRONT WHERE BOUNDARY LAYER HODOGRAPHS ARE SMALLER.
CONDITIONAL/MRGL WIND/TORNADO POTENTIAL EXISTS WITH STG DEPENDENCE
ON MESOSCALE BOUNDARY EFFECTS...CLOUD/PRECIP INFLUENCES AND
CONVECTIVE MODE. UNCONDITIONAL SVR PROBABILITIES STILL ARE TOO LOW
TO WARRANT CATEGORICAL RISK AREA ATTM...PENDING INTERDEPENDENT
MORNING CONVECTIVE AND FRONTAL TRENDS.
FARTHER W ACROSS E-CENTRAL/SE TX...LOW LEVEL MOISTENING AHEAD OF
COLD FRONT MAY SUPPORT CONDITIONAL CONVECTIVE POTENTIAL...AMIDST
FAVORABLE DEEP-LAYER SHEAR FOR SVR. HOWEVER...FOCI FOR LIFT IN THIS
AIR MASS APPEAR NEBULOUS ATTM...AND CAP SHOULD STRENGTHEN WITH WWD
EXTENT ACROSS ERN/SRN TX TOWARD AREAS WHERE BOUNDARY LAYER WILL
BECOME TOO DRY.
..EDWARDS.. 02/13/2009
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