SWODY1
SPC AC 190512
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1212 AM CDT THU MAR 19 2009
VALID 191200Z - 201200Z
...NO SVR TSTM AREAS FORECAST...
...SYNOPSIS...
SLGT AMPLIFICATION OF UPPER AIR PATTERN IS FCST THROUGH
PERIOD...LEADING TO MEAN TROUGHING FROM LOWER GREAT LAKES TO FL AND
RIDGING FROM SASK SWD ACROSS NM TO N-CENTRAL/NERN MEX. SRN LOBE OF
SHORTWAVE TROUGH -- NOW EVIDENT IN MOISTURE CHANNEL IMAGERY FROM NRN
QUE SWWD ACROSS UPPER GREAT LAKES AND WI -- IS FCST TO AMPLIFY AND
DIG SEWD ACROSS LOWER GREAT LAKES AND CENTRAL/NRN APPALACHIANS.
ASSOCIATED SFC COLD FRONT -- INITIALLY EVIDENT FROM NY SWWD ACROSS
KY...MO BOOTHEEL...SWRN OK AND PERMIAN BASIN REGION OF W TX -- WILL
MOVE OFFSHORE MOST OF ATLANTIC COAST EXCEPT FL PENINSULA BY END OF
PERIOD...AND OVER PORTIONS NRN GULF. WRN SEGMENT OF FRONT FROM S TX
ACROSS NRN GULF MAY BE DIFFUSED BY PRESENCE OF NELY SFC WINDS ON
BOTH SIDES OF FRONT. WRN LIMB OF FRONT MAY STALL ACROSS PORTIONS
LOWER PECOS VALLEY/BIG BEND REGION DURING THIS PERIOD.
...W/SW TX...
ELY LOW LEVEL FLOW COMPONENT EXPECTED ACROSS THIS REGION IN CONTEXT
OF INTRUSION OF WRN LOBE OF FRONTAL ZONE...ACCOMPANIED BY MESO-ALPHA
SCALE CONVERGENCE AND ADVECTION OF MRGL MOISTURE UPSLOPE. SFC
HEATING IN THIS REGIME -- AND BENEATH ELEVATED MIXED LAYER -- WILL
CONTRIBUTE TO STEEP LOW-MIDLEVEL LAPSE RATES AND WEAKENING CINH WITH
TIME DURING AFTERNOON. MLCAPE 500-1000 J/KG MAY BE REALIZED FOR
SHORT TIME WINDOW MID-LATE AFTERNOON. ENVIRONMENT OF RESULTING
ISOLATED TO WIDELY SCATTERED TSTMS WILL BE CHARACTERIZED BY STG
DIRECTIONAL SHEAR...BUT WEAK ABSOLUTE SPEEDS THROUGHOUT
TROPOSPHERE...GIVEN PROXIMITY OF UPPER RIDGING AND WEAK HEIGHT
GRADIENT ALOFT. WHILE CONDITIONAL RISK EXISTS FOR HAIL NEAR SVR
LEVELS OR STG GUSTS...UNCONDITIONAL PROBABILITIES ARE PRECLUDED BY
LACK OF MORE KINEMATIC SUPPORT FOR ORGANIZED SVR AND CONCERNS OVER
CONVECTIVE COVERAGE.
...S FL...
RESIDUAL/QUASISTATIONARY FRONTAL ZONE WILL REMAIN ACROSS
AREA...ACTING IN TANDEM WITH MESO-BETA- AND SMALLER-SCALE FORCING
FROM SEA BREEZE/OUTFLOW BOUNDARIES...DIABATIC HEATING...AND
FAVORABLE MOISTURE TO SUPPORT THREAT FOR TSTMS. GREATEST THUNDER
COVERAGE OF ANY GEN TSTM AREAS SHOULD BE HERE...WITH
SCATTERED/LOCALLY NUMEROUS TSTMS POSSIBLE IN AGGREGATE THROUGH
DAYLIGHT HOURS. STRENGTH...DURATION AND COVERAGE OF MOST FAVORABLE
SFC HEATING IS IN QUESTION GIVEN PRE-EXISTING CLOUDS/PRECIP...WHICH
ALSO LENDS CONSIDERABLE UNCERTAINTY ON CHARACTER AND STRENGTH OF
BOUNDARIES TO INFLUENCE STORMS TODAY. IF AND WHERE STG HEATING CAN
OCCUR...LOW LEVEL MOISTURE SHOULD BE ADEQUATE TO OFFSET WEAK
MIDLEVEL LAPSE RATES FOR GENERATION OF FAVORABLE BUOYANCY.
LOW-MIDLEVEL WINDS AND SHEAR WILL BE WEAK...THOUGH STG UPPER FLOW
ASSOCIATED WITH SUBTROPICAL JET MAY ENHANCE MULTICELL ORGANIZATION.
SVR POTENTIAL APPEARS TOO WEAK AND CONDITIONAL FOR PROBABILITIES AOA
5 PERCENT ATTM.
...WRN OZARKS SWWD OVER PORTIONS SRN PLAINS...
ISOLATED TO WIDELY SCATTERED TSTMS MAY DEVELOP ON ELEVATED FRONTAL
SURFACE ALMOST ANYTIME THROUGHOUT PERIOD OVER REGION...AIDED BY LOW
LEVEL WAA AND TRANSPORT OF MRGL MOISTURE TO LFC. MOST PROGS DEVELOP
SOME CONVECTIVE PRECIP AT VARIOUS TIMES/LOCATIONS WITHIN THIS
SWATH...AND NAM-KF SOUNDINGS SUGGEST ELEVATED MUCAPE UP TO ABOUT 500
J/KG ROOTED BETWEEN 700-750 MB. FCST EFFECTIVE SHEAR MAGNITUDES
GENERALLY ARE WEAK...BUT DO REACH 35-40 KT IN SOME LOCALES FOR BRIEF
PERIODS AS UPPER FRINGES OF BUOYANT LAYER REACH INTO LOWER PORTION
OF JET LEVEL FLOW. OVERALL SVR POTENTIAL APPEARS TOO
WEAK/CONDITIONAL FOR OUTLOOK.
...SRN PIEDMONT AND TIDEWATER REGIONS...
MRGL THREAT FOR TSTMS EXISTS INVOF FRONTAL ZONE...MAINLY DURING
AFTERNOON HOURS WHEN SFC HEATING SUFFICIENTLY ERODES CINH. WEAKNESS
OF BOTH LOW LEVEL MOISTURE AND CONVERGENCE SHOULD LIMIT CONVECTIVE
COVERAGE...THOUGH SFC DEW POINTS LOW 50S F ARE POSSIBLE AND
SUFFICIENT FOR BUOYANCY EXTENDING INTO ICING LAYERS FOR LIGHTNING
PRODUCTION.
..EDWARDS.. 03/19/2009
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