MESOSCALE DISCUSSION 0689
   NWS STORM PREDICTION CENTER NORMAN OK
   0128 AM CDT MON MAY 02 2011
   
   AREAS AFFECTED...PORTIONS N-CENTRAL/NE TX...EXTREME SERN OK...SWRN
   AR.
   
   CONCERNING...HEAVY RAINFALL 
   
   VALID 020628Z - 020930Z
   
   HEAVY RAINFALL THREAT...NOW GROWING FROM INCREASING COVERAGE OF
   TSTMS OVER PORTIONS N TX...WILL SHIFT ENEWD ACROSS PORTIONS ARKLATEX
   REGION THROUGH REMAINDER PRE-DAWN HOURS.  TSTM CORES WILL BECOME
   MORE NUMEROUS AND TRAIN REPEATEDLY OVER SOME LOCALES...WHILE
   OFFERING PRECIP RATES 1-2 INCHES/HOUR.
   
   EXPECT ADVECTION OF MOISTURE-RICH AIR MASS -- I.E. PW GENERALLY IN
   1-1.5 INCH RANGE -- TO SUPPORT CONTINUED INCREASE IN TSTM COVERAGE
   FOR ANOTHER COUPE OF HOURS OVER CENTRAL/N-CENTRAL TX...SHIFTING
   ENEWD TOWARD ARKLATEX REGION BEFORE 12Z.  PLUME OF MOISTURE
   TRANSPORT WILL BE ASSOCIATED WITH 35-45 KT LLJ INTERACTING WITH COLD
   FRONTAL ZONE AT AND ABOVE 850-MB LEVEL...WITH COMBINATION OF
   FRONTAL/ISENTROPIC ASCENT TO LFC.  ACTIVITY WILL BE SUPPORTED
   INITIALLY BY NRN FRINGE OF FIELD OF 1000-2000 J/KG MUCAPE...ALTHOUGH
   INCREASING CONVECTIVE DENSITY AND WEAKENING OF
   ELEVATED/STORM-RELATIVE LOW-LEVEL FLOW VECTORS WILL REDUCE
   REPLENISHMENT OF BUOYANCY BY WAA WITH TIME.  AFTER ABOUT 09Z...WRN
   BRANCH OF LLJ IS EXPECTED TO VEER AND WEAKEN SOMEWHAT...BUT WILL
   SUPPORT CONTINUE PLUME OF MOISTURE TRANSPORT AND ELEVATED/ISENTROPIC
   ASCENT FOR CONVECTION SHIFTING DOWNSHEAR ACROSS THIS CORRIDOR.
   
   REF SPC MESOSCALE DISCUSSION 688 FOR COVERAGE OF SHORTER-TERM SVR
   HAIL THREAT OVER WRN PORTIONS OF THIS AREA.
   
   ..EDWARDS.. 05/02/2011
   
   
   ATTN...WFO...LZK...SHV...TSA...FWD...OUN...SJT...
   
   LAT...LON   33409352 32649488 31409828 32119919 33069784 34189514
               34379403 33409352