SWODY1
SPC AC 170535
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1135 PM CST SAT JAN 16 2010
VALID 171200Z - 181200Z
...NO SVR TSTM AREAS FORECAST...
...SYNOPSIS...
PROGRESSIVE UPPER AIR PATTERN WILL INCLUDE LOSS OF SPLIT-FLOW REGIME
OVER S-CENTRAL/SERN CONUS THIS PERIOD. SHORTWAVE TROUGH NOW
ANALYZED INVOF SRN MS/AL WILL EJECT NEWD OVER SRN/CENTRAL
APPALACHIANS DURING FIRST HALF OF PERIOD. MEANWHILE...MID-UPPER
LEVEL LOW NOW OVER NE TX IS FCST TO MOVE EWD ACROSS LOWER MS VALLEY
AROUND 17/12Z...WHILE EVOLVING INTO OPEN-WAVE TROUGH...THEN MOVING
EWD ACROSS GA/CAROLINAS. THIS TROUGH WILL ACCELERATE EWD AS IT DOES
SO...AMIDST BELT OF ENHANCED CYCLONIC FLOW INFLUENCED BY LEADING
PERTURBATION.
INITIAL/OCCLUDED SFC CYCLONE -- ANALYZED AT 17/04Z OVER E-CENTRAL MS
-- WILL MOVE NEWD INTO SRN APPALACHIANS DURING FIRST 6-9 HOURS OF
PERIOD WHILE WEAKENING. SECONDARY LOW SHOULD FORM ALONG WARM FRONT
FARTHER E BY 17/12Z AND MOVE NEWD ACROSS CAROLINAS DURING
17/12Z-17/18Z TIME FRAME...THEN EWD ACROSS SERN VA AND SRN DELMARVA
BY ABOUT 18/00Z. MEANWHILE TRAILING COLD FRONT...NOW OVER CENTRAL
GULF...WILL CROSS CAROLINAS/GA/FL.
OVER NERN PACIFIC...SHORTWAVE TROUGH IS EVIDENT IN MOISTURE CHANNEL
IMAGERY W OF NRN CA AND ORE...BETWEEN 140W-145W. TSTMS HAVE BEEN
DETECTED NEAR THIS PERTURBATION FOR MUCH OF ITS PASSAGE ACROSS
PACIFIC. ACCOMPANYING AREA OF LARGE-SCALE ASCENT ALOFT AND RELATED
COLD MIDLEVEL AIR MASS WITH THIS PERTURBATION MAY MAINTAIN GEN
THUNDER POTENTIAL ALONG ITS TRACK ENEWD INTO PORTIONS COASTAL NRN CA
AND PAC NW AROUND 18/06Z TIME FRAME...BEFORE TROUGH LIFTS NEWD AND
WEAKENS INLAND.
...SC/NC/SERN VA...
BAND OF DEEP-LAYER ASCENT -- RELATED TO LINE OF LOW-TOPPED
CONVECTION NOW DEVELOPING ACROSS PORTIONS NRN FL AND SRN GA -- IS
PROJECTED TO MOVE OFFSHORE NRN FL AND GA BY START OF
PERIOD...EXTENDING INLAND PORTIONS NERN SC AND ERN NC. NARROW WEDGE
OF MODIFIED MARINE AIR MAY EXTEND INLAND DURING MORNING ACROSS THIS
REGION AND AHEAD OF CONVECTIVE BAND...AND ALONG/S OF WARM FRONT.
THIS AIR MASS SHOULD BE CHARACTERIZED BY LOW-MID 60S F DEW
POINTS...BUT WEAK/SHORT-LIVED DIABATIC HEATING GIVEN PREDOMINANCE OF
ANTECEDENT CLOUD COVER AND PRECIP. LOW-LEVEL THETAE ADVECTION
SHOULD SUFFICE TO YIELD SLIGHTLY GREATER THAN NEUTRAL SFC-MIDLEVEL
LAPSE RATES...SUPPORTING MLCAPE IN 100-500 J/KG. AMIDST WHAT SHOULD
BE STG MID-UPPER FLOW AND NEARLY UNIDIRECTIONAL DEEP-LAYER WIND
PROFILE S OF WARM FRONT...MAIN CONCERN IS FOR ISOLATED DAMAGING
WIND...WHETHER OR NOT CAPE IS DEEP ENOUGH FOR CONVECTION TO PRODUCE
MORE THAN SPORADIC THUNDER.
FARTHER W AND DURING AFTERNOON...RELATIVELY SHALLOW/POST-FRONTAL
CONVECTION -- INCLUDING POTENTIAL FOR A FEW TSTMS -- MAY OCCUR IN
AFTERNOON ACROSS PORTIONS CAROLINAS. COMPACT ZONE OF LARGE SCALE
ASCENT IN MIDLEVELS...ACCOMPANYING EJECTING SHORTWAVE TROUGH...WILL
COMBINE WITH RESIDUAL/MRGL LOW LEVEL MOISTURE AND SFC DIABATIC
HEATING TO OFFSET AMBIENT/POSTFRONTAL CAA. THIS IN TURN MAY
DESTABILIZE LOW-MIDLEVEL THERMODYNAMIC PROFILES DEEPLY ENOUGH FOR
SOME CONVECTION TO PRODUCE THUNDER. SMALL HAIL AND STG GUSTS CANNOT
BE RULED OUT GIVEN STRENGTH OF AMBIENT WIND PROFILES...HOWEVER FCST
SOUNDINGS SUGGEST MLCAPE UNDER 200 J/KG MOST AREAS AND MUCAPE UP TO
500 J/KG.
...FL...
TRAILING PORTION OF CONVECTIVE/ASCENT BAND IS EXPECTED TO WEAKEN
FROM 12Z ONWARD AS IT MOVES EWD ACROSS PENINSULA...RELATED TO
COMBINATION OF
1. EJECTION OF UPPER LEVEL PERTURBATIONS AWAY FROM AREA....AND
2. VEERING WARM-SECTOR FLOW THAT WILL SERVE TO REDUCE BOTH LOW-LEVEL
SHEAR AND CONVERGENCE.
GIVEN ALREADY FEEBLE LAPSE RATES OVER THIS REGION...LACK OF
ADDITIONAL DESTABILIZATION ALOFT AND TENDENCY FOR WEAKENING BOUNDARY
LAYER FORCING WITH TIME WILL RENDER ONLY MRGL THUNDER
POTENTIAL...AND SVR THREAT TOO SMALL/CONDITIONAL FOR AOA 5-PERCENT
UNCONDITIONAL GRID PROBABILITIES.
..EDWARDS.. 01/17/2010
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