SPC AC 131723
   
   DAY 2 CONVECTIVE OUTLOOK  
   NWS STORM PREDICTION CENTER NORMAN OK
   1223 PM CDT TUE MAY 13 2008
   
   VALID 141200Z - 151200Z
   
   ...THERE IS A SLGT RISK OF SVR TSTMS ACROSS A LARGE PORTION OF THE
   SRN PLAINS EWD INTO THE MID-SOUTH/LWR MS VLY...
   
   ...SYNOPSIS...
   UPR LOW OVER AZ WILL BEGIN TO EJECT NEWD AND WEAKEN ACROSS THE SRN
   PLAINS AS ADDITIONAL ENERGY DIGS DOWN THE BACKSIDE OF THE LONGER
   WAVE ROCKIES TROUGH ON WEDNESDAY.  MEANWHILE...A NRN STREAM WAVE
   WILL CONTINUE EWD ACROSS THE GRTLKS REGION WITH A BROAD SUB-TROPICAL
   RIDGE ACROSS THE ERN SEABOARD/SERN STATES.
   
   IN THE LOWER LEVELS...A COLD FRONT ATTENDANT TO THE NRN WAVE WILL
   SETTLE SEWD THROUGH THE GRTLKS...OH VLY AND PARTS OF AR...OK AND N
   TX TODAY.  WRN PARTS OF THIS FRONT WILL STALL AS THE UPSTREAM SYSTEM
   EJECTS NEWD TONIGHT AND WEDNESDAY.  A WEAK LOW WILL EVOLVE ALONG
   THIS FRONT FROM WCNTRL TX NEWD INTO THE RED RIVER VLY DURING THE
   COURSE OF THE DAY WITH A DRYLINE MIXING EWD INTO CNTRL TX.  THE
   FRONT AND DRYLINE WILL BE THE PRIMARY FOCAL POINTS FOR PSBL SVR
   TSTMS DURING WEDNESDAY AND WEDNESDAY NIGHT.  
   
   ...SRN PLAINS TO THE MID-SOUTH/LWR MS VLY...
   THERE WILL LIKELY BE SEVERAL TSTM CLUSTERS ONGOING AT 12Z WEDNESDAY
   ACROSS A LARGE PART OF NRN/ERN TX...SRN OK NEWD INTO THE MID-SOUTH
   ALONG/N OF THE STALLING FRONT.  THERMODYNAMIC/KINEMATIC SET-UPS
   APPEAR FAVORABLE FOR MAINTAINING STRONG-SVR TSTMS FOR MOST OF THE
   DAY ALONG THE ERN PERIPHERY OF STRONGER EML OVER THE MID-SOUTH/LWR
   MS VLY.  MODELS MAINTAIN A WEAK SSWLY BRANCH OF THE LLJ INTO
   LA...AR...NRN/WRN MS AND WRN TN INTO THE EVENING HOURS.  GIVEN STEEP
   MID-TROPOSPHERIC LAPSE RATES AND SUPERCELLULAR EFFECTIVE VERTICAL
   SHEAR...ORGANIZED...PRIMARILY ELEVATED STORMS WILL BE POSSIBLE WITH
   LARGE HAIL.  IF SRN/WRN EDGES OF ANY SUSTAINED STORM CLUSTER CAN
   ROOT INTO THE WARMING BOUNDARY LAYER ACROSS THE ERN TX...AR...LA...A
   TORNADO OR TWO CANNOT BE RULED OUT.
   
   MEANWHILE...DURING THE COURSE OF THE AFTN...AIR MASS W OF THE E
   TX/AR/LA STORMS WILL HEAT WHILE MAINTAINING MODEST LOW-LEVEL
   MOISTURE.  STEEP LAPSE RATES CAPPING OFF THIS MOISTURE WILL
   CONTRIBUTE TO VERY UNSTABLE CONDITIONS WITH MLCAPES APPROACHING 3000
   J/KG FROM NWRN TX SWD ALONG/AHEAD OF THE DRYLINE INTO SCNTRL TX. 
   APPROACH OF THE UPR LOW /MINUS 18 DEG C TEMPS/ WILL WEAKEN THE
   CAP...BOOST THE DRYLINE CIRCULATION AND LIKELY LEAD TO TSTM
   INITIATION BY EARLY AFTN.  PRESENCE OF 50-60 KTS OF 0-6KM SHEAR
   ACROSS THE DRYLINE AND MAGNITUDE OF LAPSE RATES SUGGEST POTENTIAL
   FOR VERY LARGE HAIL PRODUCING SUPERCELLS.  ACTIVITY WILL MOVE TOWARD
   SCNTRL OK...NCNTRL TX...AND THE WRN HILL COUNTRY BY DARK.
   
   VERTICAL SHEAR IS EXPECTED TO WEAKEN WITH TIME DURING THE EVENING
   WITH THE LOW-LEVEL FLOW GENERALLY WEAK DURING THE ENTIRE DAY/NIGHT. 
   THUS...TORNADO THREAT WILL NOT BE TERRIBLY HIGH...THOUGH ONE OR TWO
   CANNOT BE RULED OUT WITH THE INITIAL CELLS.  OTHERWISE...AN UPSCALE
   GROWTH INTO LOOSELY ORGANIZED CLUSTERS WITH DMGG WINDS/HAIL WILL
   SPREAD ENEWD ACROSS SRN OK...NRN/CNTRL TX TOWARD THE ARKLATEX/OZARKS
   OVERNIGHT.
   
   ..RACY.. 05/13/2008
   
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