DAY1SVR: Day 1 Convective Outlook

ACUS01 KWNS 051257
SWODY1
SPC AC 051255

DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0655 AM CST THU DEC 05 2013

VALID 051300Z - 061200Z

...NO SVR TSTM AREAS FORECAST...

...SYNOPSIS...
IN MID-UPPER LEVELS...POSITIVELY TILTED LONGWAVE TROUGH WILL PERSIST
OVER WRN CONUS...TRANSVERSED BY SEVERAL SHORTWAVES. LEADING
PERTURBATION -- NOW MANIFEST AS UPPER LOW OVER NWRN ONT JUST N OF MN
BORDER -- SHOULD EJECT NEWD ACROSS JAMES BAY THROUGH PERIOD.
TRAILING PERTURBATION OVER SK WILL MOVE SLOWLY SWD/SEWD AND
ELONGATE...HELPING TO MAINTAIN BROADER REGIME OF CYCLONIC FLOW ALOFT
OVER N-CENTRAL/NWRN CONUS. LOW-AMPLITUDE SHORTWAVE TROUGH -- NOW
EVIDENT IN MOISTURE CHANNEL IMAGERY OVER SRN NV AND SRN/CENTRAL CA
-- WILL EJECT NEWD AND DAMPEN...SUCH THAT FAIRLY STRAIGHT STREAM OF
RELATIVELY MAXIMIZED FAST MID-UPPER FLOW IS MAINTAINED FROM SRN HIGH
PLAINS TO GREAT LAKES.

AT SFC...12Z ANALYSIS SHOWED INTENSE COLD FRONT FROM WRN OH SWWD
ACROSS WRN PORTIONS KY/TN...SRN AR...AND S-CENTRAL TX. BY
00Z...FRONT SHOULD REACH WRN NY...WV...NWRN AL...SWRN LA...AND DEEP
S TX. EXPECT SRN SEGMENT OF FRONT TO DECELERATE UNDER NEARLY
PARALLEL FLOW ALOFT...WITH BOUNDARY REACHING NEW ENGLAND...MD...SRN
APPALACHIANS...AND S-CENTRAL LA BY END OF PERIOD.

...CENTRAL/ERN GULF COAST REGION TO ERN KY/SWRN VA...
SCATTERED TO WIDELY SCATTERED TSTMS ALREADY ARE PRESENT IN THIN/BKN
BAND ALONG/AHEAD OF SFC COLD FRONT...FROM SRN OH TO ERN AR. THIS
BAND WILL TRANSLATE EWD IN STEP WITH FRONT AND SHOULD BACKBUILD SWWD
AS INDIVIDUAL CONVECTIVE COMPONENTS MOVE NEWD...FOR NET EXPANSION
THROUGH MUCH OF TODAY. NRN PORTION WILL OUTPACE
PRECURSORY/WARM-SECTOR DESTABILIZATION OF SFC PARCELS ENOUGH TO
MITIGATE ALREADY MRGL/CONDITIONAL SVR POTENTIAL WITH TIME.
HOWEVER...AREAS FROM MS DELTA REGION TO MIDDLE-ERN TN AND PERHAPS
ERN KY SHOULD EXPERIENCE SUFFICIENT PREFRONTAL SFC THETAE ADVECTION
TO RENDER SFC-BASED EFFECTIVE INFLOW PARCELS...AMIDST SFC DEW POINTS
MOSTLY 60S F WITH SOME 70S NEAR GULF COAST. THIS FACTOR WILL OFFSET
WEAK LAPSE RATES ALOFT ENOUGH TO RENDER MLCAPE 500-800 J/KG OVER
PORTIONS MS/AL. CAPE FIELD WILL DECREASE IN MAGNITUDE AND GET
NARROWER IN BREADTH WITH NWD EXTENT. 35-40 KT EFFECTIVE SHEAR AND
100-200 J/KG 0-1 KM SRH ARE FCST IMMEDIATELY AHEAD OF FRONT.

ISOLATED DAMAGING GUSTS ARE POSSIBLE AND A TORNADO CANNOT BE
DEFINITIVELY RULED OUT...THUS MRGL PROBABILITIES. HOWEVER...OVERALL
ORGANIZATION/COVERAGE WILL BE LIMITED AMIDST WEAK LAPSE
RATES/BUOYANCY...LACK OF ANY SUBSTANTIAL MID-UPPER LEVEL FORCING FOR
ASCENT...PRESENCE OF STRONGEST DEEP-LAYER FLOW/SHEAR BEHIND SFC
FRONT...NEUTRAL OR SLIGHTLY POSITIVE MID-UPPER HEIGHT CHANGES...AND
FLOW ALOFT BEING PARALLEL TO FRONT RESULTING IN SLGT NET ANAFRONTAL
CHARACTER.

INITIALLY SEPARATE AREA OF MOSTLY SHALLOW CONVECTION AND SHOWERS MAY
DEVELOP/EXPAND PERSIST FROM GULF NEWD ACROSS PORTIONS SERN MS AND
AL...PERHAPS WRN GA. THIS ACTIVITY WILL OCCUR IN ERN PORTIONS OF
LONGSTANDING LOW-LEVEL WAA/MOISTURE TRANSPORT PLUME...E OF EDGE OF
EML-RELATED CAPPING LAYER EVIDENT IN 12Z JAN/LIX RAOBS. WHILE
BUOYANCY DEEP ENOUGH TO REACH IDEAL THERMAL LAYERS FOR LTG
PRODUCTION IS IN DOUBT...AT LEAST ISOLATED TSTM ARE POSSIBLE. OCNL
LOW-MIDDLE LEVEL STORM-SCALE ROTATION ALSO MAY DEVELOP GIVEN FCST
VEERING OF WINDS WITH HEIGHT AND RESULTANT PROGS OF 100-200 J/KG OF
0-1 KM SRH. HOWEVER...WEAK LOW-LEVEL FORCING AND LACK OF MORE
ROBUST BUOYANCY WILL KEEP TORNADO THREAT VERY MRGL/CONDITIONAL AT
MOST.

..EDWARDS/GARNER.. 12/05/2013

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