SPC AC 310832

   DAY 3 CONVECTIVE OUTLOOK  
   NWS STORM PREDICTION CENTER NORMAN OK
   0232 AM CST WED DEC 31 2014

   VALID 021200Z - 031200Z

   ...THERE IS A MRGL RISK OF SVR TSTMS WEST-CENTRAL GULF COAST
   REGION...

   ...SUMMARY...
   THUNDERSTORMS MAY AFFECT A BROAD SWATH FROM SOUTHWEST TEXAS TO
   ALABAMA.  A FEW OF THESE MAY REACH SEVERE LEVELS NEAR THE GULF COAST
   OF EXTREME SOUTHEAST TEXAS...LOUISIANA AND MISSISSIPPI.

   ...SYNOPSIS...
   IN MID-UPPER LEVELS...SPLIT-FLOW REGIME WILL CONTINUE THROUGH DAY-3
   PERIOD...BUT WITH CONJOINMENT BEGINNING OVERNIGHT.  CYCLONE NOW
   DIGGING SSWWD ACROSS SIERRAS IS EXPECTED TO PIVOT/EJECT IN TWO PARTS
   ON DAY 2.  NRN LOBE THEN WILL WEAKEN AND ACCELERATE EWD ACROSS GREAT
   LAKES THIS PERIOD.  MEANWHILE...SRN PORTION WILL BEGIN DAY 3 AT
   2/12Z AS CLOSED 500-MB CYCLONE OVER ERN AZ OR WRN NM...WITH
   ASSOCIATED TROUGH SWWD ACROSS SONORA TO CENTRAL BAJA.  LOW/TROUGH
   THEN WILL MOVE ENEWD TO NEWD ACROSS SRN ROCKIES AND SRN PLAINS
   THROUGH 3/12Z...AS STG SHORTWAVE TROUGH NOW S OF ALEUTIANS DIGS SEWD
   ALONG NRN ROCKIES TO NRN HIGH PLAINS.

   PROGS NOW ARE SEGREGATED INTO TWO CAMPS WITH AMPLITUDE/POSITION OF
   THIS FEATURE BY END OF PERIOD...
   1. FASTER AND GENERALLY LESS-AMPLIFIED OPERATIONAL NAM/SPECTRAL AND
   MOST NMM/NMM-B SREF MEMBERS...
   2. SLOW ECMWF AND WRF-ARW MEMBERS OF SREF...LATTER CAUSING
   CONSIDERABLE SMEARING OF SREF MEAN BOTH ALOFT AND WITH SFC FIELDS.

   THIS DIVISION APPEARS TO BE RELATED TO STRENGTH AND PHASE SPEED OF
   NRN-STREAM PERTURBATION DIGGING SEWD FROM WRN CANADA...WHICH NOW
   RESIDES IN RAOB VOID OF OPEN N PAC AND EXHIBITS LITTLE APPARENT
   INITIAL ERROR WHEN COMPARING WITH SATELLITE PRESENTATIONS.  IN
   EITHER CASE...SWRN-CONUS TROUGH WILL BE FAR ENOUGH FROM SFC WARM
   SECTOR TO OFFER ONLY GLANCING INFLUENCE AS IT EJECTS...WHILE STILL
   YIELDING IMPORTANT TIMING/SPATIAL UNCERTAINTIES ON WARM SECTOR
   GEOMETRY AND ASSOCIATED SVR POTENTIAL.

   BENT SFC FRONTAL ZONE -- ITS BAROCLINICITY REINFORCED BOTH BY
   OPEN-GULF THERMAL FLUXES AND INLAND PRECIP -- SHOULD EXTEND LARGELY
   N-S OVER WRN-GULF SHELF WATERS AT START OF PERIOD...THROUGH WEAK
   WAVE LOW OFF TX COAST...THEN EWD OR ENEWD JUST OFFSHORE WRN/CENTRAL
   LA COAST.  THOUGH PROGS DIFFER CONSIDERABLY ON TIMING AND EXTENT OF
   INLAND PENETRATION OF WARM-FRONTAL SEGMENT  OVER LA...SOME PORTION
   OF WARM SECTOR SHOULD PENETRATE AT LEAST AS FAR AS SERN LA AND
   EXTREME SRN MS BEFORE 3/12Z...AND PERHAPS AS FAR E AS MOB AREA.  WRN
   SEGMENT OF FRONT SHOULD MOVE EWD ACROSS AREAS ALONG AND S OF UPPER
   TX COAST AT SOME POINT LATE DAY-3 OR THEREAFTER.

   ...WRN/CENTRAL GULF COAST AND LOWER DELTA REGION...
   ELEVATED TSTMS SHOULD OCCUR EPISODICALLY THROUGHOUT PERIOD N OF
   MARINE/WARM FRONT AND INLAND...WITH ANY SVR HAIL RISK APPEARING TOO
   WEAK/ISOLATED FOR UNCONDITIONAL PROBABILITIES ATTM.

   MAIN CONCERN WILL BE WITH ANY SFC-BASED CONVECTION THAT CAN DEVELOP
   ALONG/AHEAD OF ACCELERATING COLD FRONT OVERNIGHT. PRIMARY CONCERN IS
   HOW FAR INLAND MAY SFC-BASED BUOYANCY EXTEND...WITH ADDITIONAL
   CONSIDERATION OF STABILIZATION BY ANTECEDENT PRECIP OVER LAND. 
   SCATTERED TSTMS SHOULD FORM INVOF COLD FRONT OVER GULF...EXTENDING
   NWD ALONG ELEVATED FRONTAL SFC INLAND.  ATTM...FCST SOUNDINGS
   SUGGEST CURVED BUT SMALL TO MRGLLY SUPPORTIVE WARM-SECTOR
   HODOGRAPHS...INDICATING MRGL POTENTIAL FOR SUPERCELLS IN FREE WARM
   SECTOR.  SOMEWHAT STRONGER DEEP SPEED SHEAR WITH STRONG
   BOUNDARY-PARALLEL COMPONENT WILL EXIST ALONG COLD FRONT.  WHILE MOST
   AGGRESSIVE RETURN-FLOW/TROUGH-EJECTION SCENARIOS INDICATE SQUALL
   LINE WITH WIND OR CONDITIONAL TORNADO THREAT DEVELOPING DURING LAST
   SEVERAL HOURS OF PERIOD...UNCERTAINTY IS TOO LARGE TO DRAW MORE THAN
   MRGL CATEGORICAL SVR AREA ATTM.

   ..EDWARDS.. 12/31/2014

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   NOTE: THE NEXT DAY 3 OUTLOOK IS SCHEDULED BY 0830Z