SPC AC 201239

   DAY 1 CONVECTIVE OUTLOOK  
   NWS STORM PREDICTION CENTER NORMAN OK
   0739 AM CDT SUN APR 20 2014

   VALID 201300Z - 211200Z

   ...THERE IS A SLGT RISK OF SVR TSTMS PORTIONS WRN/NWRN TX AND SWRN
   OK...

   ...SUMMARY...
   SCATTERED THUNDERSTORMS MAY DROP SEVERE HAIL AND DAMAGING GUSTS FROM
   THE TEXAS SOUTH PLAINS ACROSS THE CAPROCK AREA TO NORTHWEST TEXAS
   AND PERHAPS SOUTHWESTERN OKLAHOMA...MAINLY LATE AFTERNOON INTO EARLY
   EVENING.

   ...SYNOPSIS...
   NEARLY ZONAL MIDDLE-UPPER-LEVEL FLOW COURSES OVER NRN TIER OF
   STATES...PERTURBED PRIMARILY BY SHORTWAVE TROUGH NOW MOVING EWD FROM
   NRN ROCKIES.  THIS FEATURE WILL MOVE EWD ALONG CANADIAN BORDER AND
   REACH NRN MN BY END OF PERIOD.  SPLIT FLOW WILL PERSIST AROUND TWO
   PROGRESSIVE SRN-STREAM TROUGHS.  FIRST OF THESE CONTAINS EMBEDDED
   MID-UPPER-LEVEL LOW NOW OFFSHORE CAROLINAS...AND FCST TO MOVE SLOWLY
   ENEWD OVER ATLC WATERS THROUGH REMAINDER PERIOD.  UPSTREAM SHORTWAVE
   RIDGING WILL SHIFT EWD OVER LOWER-MIDDLE MS VALLEY TODAY...REACHING
   CENTRAL/SRN APPALACHIANS BY END OF PERIOD.  GRADUALLY DEAMPLIFYING
   PERTURBATION -- FORMERLY CONTAINING CLOSED 500-MB LOW -- IS EVIDENT
   IN MOISTURE CHANNEL IMAGERY FROM SRN CO SSWWD ACROSS NM AND NWRN
   MEX.  500-MB TROUGH SHOULD CONTINUE SLOW WEAKENING TREND...WHILE
   ADVANCING ENEWD TO NEAR HLC-CDS-6R6 AXIS BY 00Z AND TOP-OKC-ERV AXIS
   BY 12Z. 

   AT SFC...WEAK LOW NOW EVIDENT OVER SERN CO IS PART OF LEE TROUGHING
   REGIME EXTENDING FROM MT TO SW TX.  THIS LOW SHOULD MOVE SLOWLY SEWD
   TO OK PANHANDLE OR NRN TX PANHANDLE BY 00Z...WITH WEAK COLD FRONT
   SWWD OVER NERN NM...TROUGH SSWWD ACROSS PERMIAN BASIN...AND DRYLINE
   BECOMING BETTER DEFINED INVOF LEE TROUGH.  BY 12Z...LOW SHOULD REACH
   SWRN OK...WEAK FRONT TO SERN NM...DRYLINE/TROUGH SWWD OVER SERN
   CORNER OF NM.  INITIALLY SEPARATE FRONTAL ZONE ASSOCIATED WITH
   NRN-STREAM TROUGH...AND EXTENDING FROM UPPER MS VALLEY SWWD OVER
   NEB...ALSO MAY ENCOURAGE TSTM DEVELOPMENT THIS AFTN AND EVENING. 
   HOWEVER...VERTICAL SHEAR APPEARS TOO WEAK FOR ORGANIZED SVR THREAT. 

   ...W TX TO SWRN OK...
   SCATTERED TSTMS SHOULD DEVELOP THIS AFTN INVOF LEE
   TROUGH/DRYLINE...AS WELL AS OVER TX PANHANDLE ON EITHER SIDE OF SFC
   TROUGH.  THIS SHOULD OCCUR AFTER SEVERAL HOURS OF DIABATIC
   DESTABILIZATION THAT WEAKENS CINH...IN WAKE OF CLOUD/PRECIP PLUME
   NOW EXTENDING FROM PORTIONS CENTRAL/NRN OK TO W-CENTRAL TX. 
   VERTICAL JUXTAPOSITION OF SLGT LOW-LEVEL MOISTENING WITH COOLING
   TEMPS ALOFT AND SFC HEATING SHOULD CONTRIBUTE TO PLUME OF 1000-1500
   J/KG MLCAPE AHEAD OF DRYLINE BETWEEN 21-00Z.  

   TIMING OF MID-UPPER TROUGH WILL PUT IT ESSENTIALLY ATOP DRYLINE BY
   00Z...BY WHICH TIME 500-MB FLOW AOA 35 KT AND 250-MB WINDS AOA 50 KT
   SHOULD BE SE OF OKC-MAF LINE AND SHIFTING EWD IN STEP WITH TROUGH
   TRANSLATION.  WEAKER WINDS ALOFT INVOF MID-UPPER TROUGH WILL GREATLY
   LIMIT VERTICAL SHEAR AND RESTRICT POTENTIAL FOR MORE THAN TRANSIENT
   SUPERCELLULAR CHARACTERISTICS...MOSTLY WITH NWD EXTENT FROM US-380
   CORRIDOR IN NW TX.  CAPPING WILL BE MORE OF A LIMITING FACTOR WITH
   SWD EXTENT FROM THERE.  MIDLEVEL LAPSE RATES WILL BE STEEPEST NEAR
   TROUGH ALOFT...WHERE COLDEST 300-600 MB LAYER AIR SHOULD PASS. AS
   SUCH...BEST OVERLAP OF AT LEAST MRGLLY FAVORABLE PARAMETERS APPEARS
   MOST PROBABLE INSIDE 15% WIND/HAIL AND CATEGORICAL SLGT LINE. 
   THOUGH SOME CONVECTION SHOULD PERSIST WELL INTO OVERNIGHT HOURS OVER
   PARTS OF N TX AND/OR SRN OK...SVR THREAT SHOULD WANE WITH EWD EXTENT
   INTO STABILIZING BOUNDARY LAYER.

   ..EDWARDS/ROGERS.. 04/20/2014

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