SWODY1
SPC AC 130059
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0659 PM CST SAT DEC 12 2009
VALID 130100Z - 131200Z
...NO SVR TSTM AREAS FORECAST...
...SYNOPSIS...
BROAD BELT OF NEARLY ZONAL FLOW PREVAILS ACROSS MOST OF CONUS FROM
SWRN DESERTS TO ATLANTIC COAST...PERTURBED MOST STRONGLY BY
SHORTWAVE TROUGH NOW LOCATED JUST OFFSHORE NRN/CENTRAL CA COAST.
THIS TROUGH WILL MOVE INLAND OVERNIGHT TO NWRN NV AND S-CENTRAL CA.
FARTHER DOWNSTREAM...MOISTURE CHANNEL IMAGERY INDICATES SUBTLE
TROUGH MOVING NEWD ACROSS PORTIONS KS/OK...FCST TO REACH MID MS
VALLEY REGION BY 12Z.
AT SFC...HIGH LEFT BEHIND PRIOR FROPA -- INITIALLY INVOF COASTAL
DELMARVA REGION -- IS FCST TO CONTINUE RETREATING NEWD AND OFFSHORE.
AS THIS OCCURS...MARINE AIR MASS WILL APCH LA/AL/MS GULF COASTS IN
ADVANCE OF WEAK FRONTAL-WAVE LOW NOW ANALYZED JUST OFFSHORE BPT
AREA. WARM FRONT IS ANALYZED TO ITS E...JUST OFFSHORE LA
COAST...THEN SPLITTING INTO DOUBLE-STRUCTURED FRONTAL ZONE -- ONE
BRANCH EWD ACROSS N-CENTRAL FL AND ANOTHER SEWD OVER E-CENTRAL GULF.
SRN BRANCH REPRESENTS MORE PURE MARITIME/TROPICAL AIR MASS...WHILE
NRN BRANCH MARKS SRN PERIPHERY OF RESIDUAL/STABLE POLAR AIR MASS
ASSOCIATED WITH ANTICYCLONE.
REGIMES OF LOW LEVEL WAA AND MOISTURE TRANSPORT...SUPPORTING
CLUSTERS OF CONVECTION FROM LOWER MS DELTA TO SRN MO -- ARE EXPECTED
TO SHIFT ENEWD THROUGH REMAINDER PERIOD. THIS WILL LEAD TO
INCREASING THETAE ABOVE RELATIVELY COOL/STABLE BOUNDARY LAYER...AND
BUOYANCY FAVORABLE FOR TSTMS DEVELOPING OVER LOWER OH
VALLEY...PORTIONS TN VALLEY REGION AND CORRIDOR FROM SRN MS/AL TO
COASTAL SC.
...LOWER DELTA REGION TO MS/AL COASTS...
SRN BRANCH OF WARM FRONT WILL MERGE FROM W-E WITH NRN BRANCH OVER
NRN GULF AND NEAR MOUTH OF MS RIVER...BRINGING NEARLY SFC-BASED
LIFTED PARCELS ACROSS COASTAL MARSHES OF EXTREME SERN LA. THIS AIR
MASS MAY REACH COASTAL MS/AL/WRN FL PANHANDLE...BUT PROBABLY NOT
VERY FAR INLAND...IF AT ALL...BEFORE END OF PERIOD. SOME CONVECTION
MAY PRODUCE STG GUSTS...WITH MLCAPE 500-1000 J/KG BEING POSSIBLE
ALONG AND S OF WARM FRONT. ANOMALOUSLY LARGE MUCAPE IN LIX RAOB
APPEARS TO BE RELATED TO SPURIOUS LAYER OF AUTOCONVECTIVE LAPSE
RATES WITHIN SATURATED AIR...ATOP FRONTAL LAYER.
...MID-SOUTH TO OZARKS AND LOWER OH VALLEY REGION...
00Z SGF SOUNDING SAMPLED REGION OF LARGE-SCALE ASCENT ASSOCIATED
WITH TROUGH EJECTING FROM S-CENTRAL PLAINS...WITH ELEVATED MUCAPE TO
NEAR 1000 J/KG...BUT ONLY 15 KT EFFECTIVE SHEAR MAGNITUDE. BUOYANCY
SHOULD LESSEN WITH TIME AND NEW EXTENT AS PARENT SYSTEM
AMPLIFIES...BUT STILL SUPPORTING POTENTIAL FOR TSTMS TONIGHT FROM
OZARKS TO SRN INDIANA. VERY BRIEF/ISOLATED HAIL NEAR SVR LIMITS
CANNOT BE RULED OUT FROM MOST INTENSE CORES....HOWEVER THIS THREAT
APPEARS TOO CONDITIONAL AND WIDELY DISPERSED FOR SVR PROBABILITIES.
...CA...
ALTHOUGH POTENTIAL SHOULD DIMINISH AS MID-UPPER TROUGH MOVES INLAND
AND DIABATIC SFC COOLING OCCURS...ISOLATED TO WIDELY SCATTERED
THUNDER STILL IS POSSIBLE IN REGION OF RELATED MID-UPPER LEVEL
DESTABILIZATION/ASCENT. FCST SOUNDINGS AND MODIFIED OAK RAOB
INDICATES MUCAPE 200-400 J/KG WILL REMAIN POSSIBLE FOR A FEW MORE
HOURS AHEAD OF TROUGH.
..EDWARDS.. 12/13/2009
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