SPC AC 262001

   DAY 1 CONVECTIVE OUTLOOK  
   NWS STORM PREDICTION CENTER NORMAN OK
   0201 PM CST SAT DEC 26 2015

   VALID 262000Z - 271200Z

   ...THERE IS AN ENH RISK OF SVR TSTMS FROM SERN OK INTO CNTRL AND SRN
   TX...

   ...THERE IS A SLGT RISK OF SVR TSTMS FROM WRN AR INTO CNTRL/SWRN 
   TX...

   ...THERE IS A MRGL RISK OF SVR TSTMS FROM THE OH VALLEY TO SRN 
   PLAINS...

   ...SUMMARY...
   SEVERE THUNDERSTORMS WILL BE SCATTERED TODAY THROUGH TONIGHT FROM
   SOUTH CENTRAL TEXAS NORTHEAST INTO THE OZARKS AND LOWER OHIO VALLEY.
   THE GREATEST SEVERE POTENTIAL...INCLUDING A FEW TORNADOES...IS
   EXPECTED OVER PARTS OF CENTRAL AND NORTHEAST TEXAS AND SOUTHERN
   OKLAHOMA.

   ...TX...
   A WWD EXPANSION HAS BEEN MADE TO THE 10 PERCENT TORNADO PROBABILITY
   AREA...AND A 30 PERCENT WIND PROBABILITY HAS BEEN ADDED ACROSS PARTS
   OF CENTRAL AND SRN TX WITH THIS UPDATE. TORNADO PROBABILITY CHANGES
   WERE DONE TO ACCOUNT FOR CURRENT TORNADO WATCH AND PROSPECTS FOR AT
   LEAST A COUPLE OF TORNADOES THROUGH THIS EVENING ACROSS PORTIONS OF
   N-CNTRL TX NWD ACROSS THE RED RIVER INTO SERN OK.

   WEAK BACKGROUND ASCENT WILL CONTINUE TO ACT ON A WARM AND
   ANOMALOUSLY MOIST AIRMASS ACROSS TX AND SOUTHEAST OK TO SUPPORT
   CONTINUED ISOLATED TO SCATTERED WARM SECTOR CONVECTIVE DEVELOPMENT.
   MEANWHILE...MORE WIDESPREAD DEEP CONVECTION WILL BE SUSTAINED BY
   SLAB ASCENT ON THE COOL SIDE OF A PRONOUNCED COLD FRONT SETTLING
   GRADUALLY SOUTH-SOUTHEAST ACROSS NWRN TX.

   WARM SECTOR CONVECTIVE DEVELOPMENT IS FORECAST TO REMAIN RELATIVELY
   SPARSE IN COVERAGE THROUGH THIS EVENING. HOWEVER...ANY STORMS THAT
   CAN DEVELOP WITHIN AN AREA BOUNDED BY TX HILL COUNTRY NORTH ACROSS
   THE RED RIVER INTO SERN OK...WILL EXIST IN A SUPPORTIVE REGIME FOR
   TORNADOES...HAIL AND DAMAGING WINDS. DESPITE GENERALLY WEAK ASCENT
   ACROSS THE WARM SECTOR....POCKETS OF STRONGER SFC HEATING MAY AID
   STORM INITIATION WHERE EFFECTIVE SRH IS ON THE ORDER OF 200 M2/S2
   AND LFC IS AOB 1 KM. FURTHERMORE...STORMS IN PROXIMITY TO STRONG
   WARM FRONT OVER ERN OK WILL ALSO POSE A THREAT FOR TORNADOES.

   STRONGER FORCING FOR ASCENT ARRIVES ACROSS WRN/S-CNTRL TX LATER
   TONIGHT AS POTENT UPPER LOW AND SPEED MAX DEVELOP ACROSS THE RIO
   GRANDE VALLEY FROM NRN MEXICO. A FOCUSED AREA OF SEVERE STORM
   POTENTIAL MAY EVOLVE AS FORCING AND STRENGTHENING DEEP-LAYER FLOW
   FIELDS ACT ON MOIST WARM SECTOR EXPECTED TO RESIDE FROM THE EDWARDS
   PLATEAU EWD. IN ADDITION...INTERSECTION OF COLD FRONT AND SURGING
   PACIFIC FRONT WILL PROVIDE FOCUSED ASCENT ALLOWING STORMS TO PERSIST
   IN THE PRESENCE OF INCREASING SHEAR AND FORCING...COMMENCING AND
   CONTINUING AROUND MIDNIGHT CST. LATEST AVAILABLE STORM SCALE
   GUIDANCE...ACROSS A VARIETY OF MODEL CORES...SUGGEST THE PROSPECT OF
   A COMPACT AND FAST-MOVING LINEAR MCS EVOLVING AND SPREADING EAST
   ACROSS THE AREA DEPICTED BY 30 PERCENT SEVERE WIND PROBABILITY
   CONTOUR IN THIS UPDATED OUTLOOK.

   ..CARBIN.. 12/26/2015

   .PREV DISCUSSION... /ISSUED 1029 AM CST SAT DEC 26 2015/

   ...SYNOPSIS...

   MID AND UPPER-LEVEL WIND MAXIMA FROM SRN CA INTO BAJA AND THE GULF
   OF CA WILL DEVELOP SEWD INTO NWRN MEXICO...CONTRIBUTING TO THE
   OVERALL DEEPENING OF THE PARENT CLOSED LOW AS IT TRACKS FROM SRN AZ
   TO FAR WRN TX AND CHIHUAHUA MEXICO BY 12Z/SUNDAY.  THIS PATTERN
   EVOLUTION WILL RESULT IN A CORRIDOR OF MID-LEVEL HEIGHT FALLS/DCVA
   SPREADING EWD ACROSS NWRN MEXICO INTO SWRN TX THIS PERIOD.

   AT THE SURFACE...AN AREA OF LOW PRESSURE DEEPENING OVER CHIHUAHUA
   MEXICO WILL DEVELOP GENERALLY EWD ALONG A SWD-SURGING COLD FRONT
   INTO THE TX BIG BEND BY THIS EVENING BEFORE REACHING THE TX HILL
   COUNTRY BY THE END OF THE FORECAST PERIOD. 

   ...SRN PLAINS INTO OZARK PLATEAU THIS AFTERNOON THROUGH TONIGHT...

   12Z RAOB DATA INDICATE THE PRESENCE OF A VERY MOIST AIR MASS IN
   PLACE ACROSS THE PRE-FRONTAL WARM SECTOR WITH LOWEST-100-MB
   MEAN-MIXING RATIOS OF 13-16 G/KG BENEATH MODESTLY STEEP MID-LEVEL
   LAPSE RATES OF AROUND 7 C/KM.  AND WHILE WIDESPREAD CLOUDS WILL
   LIMIT THE DEGREE OF BOUNDARY-LAYER WARMING...THE RICH LOW-LEVEL
   MOISTURE WILL CONTRIBUTE TO AFTERNOON MLCAPE VALUES OF 1000-1500
   J/KG.

   TSTMS /MAINLY ELEVATED/ ARE RAPIDLY DEVELOPING THIS MORNING ACROSS
   WRN NORTH TX AND OK WITHIN A ZONE OF STRONG WAA AND ISENTROPIC
   ASCENT ALONG A 40-50 KT LLJ...IMMEDIATELY TO THE NORTH OF A SURFACE
   FRONT STRETCHING FROM A WEAK LOW NEAR FST NEWD TO NEAR SPS AND THEN
   EWD TO N OF TXK.  SOME OF THESE ELEVATED STORMS MAY CONTAIN
   MARGINALLY SEVERE HAIL.

   THE STRONG LOW-LEVEL WAA SHOULD ALLOW FOR THE CONTINUED NWD MOVEMENT
   OF THE AFOREMENTIONED FRONT THROUGH THE RED RIVER VALLEY AND OZARK
   PLATEAU BEFORE IT IS OVERTAKEN BY A POWERFUL COLD FRONT SURGING SWD
   THROUGH THE SRN HIGH PLAINS.  AS SUCH...THE GREATEST POTENTIAL FOR
   SURFACE-BASED SUPERCELLS --AND ATTENDANT TORNADO THREAT-- WILL EXIST
   WITHIN THIS WAA REGIME --AHEAD OF THE COLD FRONT-- THIS AFTERNOON
   INTO EVENING FROM PORTIONS OF CNTRL TX INTO SERN OK AND WRN AR WHERE
   A FAVORABLE OVERLAP OF MODERATE INSTABILITY AND STRONG VERTICAL
   SHEAR WILL RESIDE.  OTHERWISE...EXPECT STORMS FORMING ALONG THE COLD
   FRONT TO QUICKLY BECOME UNDERCUT AND SLIGHTLY ELEVATED WITH THE
   PRIMARY HAZARDS BEING MARGINALLY SEVERE HAIL AND LOCALLY STRONG
   WINDS. 

   LATEST MODEL GUIDANCE IS CONSISTENT WITH EARLIER DATA IN SUGGESTING
   THE DEVELOPMENT OF A SEPARATE BAND OF TSTMS OVER SWRN TX THIS
   EVENING WITHIN THE PRIMARY ZONE OF DEEP-LAYER FORCING FOR ASCENT
   PRECEDING THE UPPER LOW.  THIS ACTIVITY WILL SPREAD EWD ACROSS THE
   EDWARDS PLATEAU REGION TONIGHT WITH A RISK FOR DAMAGING WINDS AND
   HAIL BEFORE BECOMING UNDERCUT BY THE SWD-SURGING COLD FRONT.

   ...MID SOUTH INTO OH VALLEY...

   MULTIPLE CLUSTERS OF TSTMS ARE ONGOING FROM THE MID SOUTH INTO THE
   OH VALLEY ALONG AND TO THE NORTH OF A WARM FRONT LIFTING NWD INTO
   THE LOWER-OH VALLEY.  WIDESPREAD CLOUDS AND POOR LAPSE RATES WILL
   LIMIT THE DEGREE OF AIR MASS DESTABILIZATION WITH THE MAJORITY OF
   TSTMS LIKELY REMAINING SLIGHTLY ELEVATED TO THE NORTH OF THE
   POLEWARD-MOVING WARM SECTOR.  NONETHELESS...THE PRESENCE OF
   RELATIVELY STRONG VERTICAL SHEAR INVOF THE SURFACE FRONT SUGGESTS
   THAT A LOW-PROBABILITY RISK FOR SEVERE WEATHER WILL EXIST WITH ANY
   STORMS THAT CAN BECOME SURFACE-BASED OR NEAR-SURFACE-BASED. 

   FOR ADDITIONAL NEAR-TERM GUIDANCE...SEE MCD 2064.

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