SWODY1
SPC AC 200049
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0749 PM CDT THU MAR 19 2009
VALID 200100Z - 201200Z
...NO TSTM AREAS FORECAST...
...SYNOPSIS...
UPPER AIR PATTERN IS CHARACTERIZED BY TROUGHING FROM QUE ACROSS
LOWER GREAT LAKES AND SRN APPALACHIANS...WHEREAS MEAN RIDGE
PREDOMINATED FROM N-CENTRAL/NERN MEX NNWWD ALONG HIGH PLAINS TO ERN
MT. SHORTWAVE TROUGH -- NOW EVIDENT IN MOISTURE CHANNEL IMAGERY
FROM SRN ONT WSWWD TO NRN IL -- IS FCST TO DIG ESEWD TOWARD SYNOPTIC
TROUGH POSITION...CROSSING CENTRAL APPALACHIANS AND WRN NY BY END OF
PERIOD. SECONDARY AND CONVECTIVELY ENHANCED PERTURBATION IN NW FLOW
WILL MOVE FROM SERN OK SEWD TO LOWER MS DELTA REGION AND WEAKEN.
AT SFC...WAVY COLD FRONTAL ZONE IS EVIDENT FROM CENTRAL/ERN NC WSWWD
ACROSS CENTRAL AL...CENTRAL/NRN LA...THEN WNWWD THROUGH WEAK WAVE
LOW NEAR MWL. FRONTAL ZONE THEN BECOMES DIFFUSE AND INTERMINGLED
WITH DRYLINE SWWD ACROSS CONCHO VALLEY AND LOWER PECOS RIVER AREA OF
SW TX...BECOMING BETTER DEFINED AGAIN AGAINST HIGHER TERRAIN OF
TX/MEX BORDERLANDS BETWEEN BIG BEND AND ELP. FRONT SHOULD CONTINUE
TO MOVE EWD OFFSHORE CAROLINAS...WHILE BECOMING MORE DIFFUSE OVER
MUCH OF GULF COAST REGION AMIDST NELY FLOW ON BOTH SIDES. FRONT
ALSO IS EXPECTED TO CONTINUE WEAKENING OVER N-CENTRAL THROUGH SW TX
UNDER UPPER RIDGING.
...PORTIONS TX/OK...
LAST VIS IMAGERY SHOWS AGITATED AREA OF LOW CLOUDS FROM NEAR RED
RIVER -- NW DAL -- SSWWD ACROSS SEP/BWD AREAS...INCLUDING CLUMPS OF
TCU BETWEEN SEP-BWD. THIS COINCIDES WITH AREA OF WEAK BUT
RELATIVELY MAXIMIZED LOW LEVEL CONVERGENCE...BUT THIS MAY NOT BE
SUFFICIENT TO OVERCOME SOMEWHAT ELEVATED LAYER OF CAPPING -- BETWEEN
650-700 MB -- EVIDENT IN 00Z FWD RAOB. ISOLATED/BRIEF CB STILL MAY
DEVELOP BEFORE ABOUT 02Z...HOWEVER PROBABILITY DIMINISHES WITH TIME
AS SFC DIABATIC COOLING FURTHER REDUCES MLCAPE AND STRENGTHENS CINH.
PERSISTENT REGIME OF ELEVATED CONVECTIVE DEVELOPMENT OVER OK APPEARS
TO BE DECLINING IN COVERAGE AND INTENSITY AS AFOREMENTIONED WEAK
SHORTWAVE MOVES AWAY FROM AREA. VERY BRIEF/ISOLATED THUNDER STILL
MAY BE POSSIBLE WITHIN ASSOCIATED PLUME OF CONVECTION/PRECIP FOR
ANOTHER HOUR OR TWO...OVER PORTIONS SE OK AND NE TX.
HOWEVER...UNCONDITIONAL THUNDER PROBABILITIES APPEAR TO HAVE
DIMINISHED BELOW 10 PERCENT CATEGORICAL OUTLOOK CRITERIA.
IN RESPONSE TO HEIGHT/PRESSURE FALLS IN LEE OF SRN/CENTRAL
ROCKIES...LOW LEVEL WINDS FROM SFC-850 MB ARE FCST TO BACK AND
STRENGTHEN OVERNIGHT OVER PORTIONS NRN/WRN TX NNWWD ACROSS CENTRAL
HIGH PLAINS. ALTHOUGH 850 MB WINDS SHOULD STRENGTHEN OVER RED RIVER
REGION AND OK AS A RESULT...NET SPEED DIVERGENCE IS PROGGED AT THAT
LEVEL GIVEN EVEN STRONGER FLOW DOWNSTREAM OVER ERN CO...NEB AND SD.
WHILE ADDITIONAL/ELEVATED CONVECTIVE DEVELOPMENT OVER OK CANNOT BE
RULED OUT ENTIRELY...PROBABILITIES APPEAR TOO WEAK/CONDITIONAL FOR
OUTLOOK.
NELY/UPSLOPE FLOW BEHIND REMNANTS OF FRONT HAS ADVECTED MRGL
MOISTURE UPSLOPE AND CONTRIBUTED TO OROGRAPHIC ASCENT...IN SUPPORT
OF TRANSIENT CB DEVELOPMENT SINCE 21Z NEAR RIO GRANDE NW OF BIG
BEND. WITH LOSS OF SFC HEATING...PRIND LIFT AND INSTABILITY EACH
WILL BECOME TOO WEAK FOR ENOUGH THUNDER POTENTIAL TO MAINTAIN
CATEGORICAL OUTLOOK THAT FAR SW.
...NC/SC...
ISOLATED TO WIDELY SCATTERED TSTMS FROM EARLIER THIS AFTERNOON --
EMBEDDED WITHIN BROADER SW-NE ALIGNED PRECIP PLUME...HAVE DIMINISHED
ACROSS REGION. COMBINATION OF WEAK MIDLEVEL LAPSE RATES...LOSS OF
SFC DIABATIC HEATING...POSTFRONTAL CAA AND PRECIP-RELATED
STABILIZATION SHOULD PRECLUDE ENOUGH DESTABILIZATION TO MAINTAIN GEN
TSTM AREA.
..EDWARDS.. 03/20/2009
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