MESOSCALE DISCUSSION 2000
   NWS STORM PREDICTION CENTER NORMAN OK
   0741 AM CDT THU AUG 18 2011
   
   AREAS AFFECTED...PORTIONS SRN MO...NRN/ERN AR...EXTREME SWRN
   TN...NWRN MS.
   
   CONCERNING...HEAVY RAINFALL 
   
   VALID 181241Z - 181515Z
   
   POTENTIAL EXISTS FOR MERGER OF CONVECTIVE CLUSTERS OVER DISCUSSION
   AREA THAT THEN WOULD MOVE/SPREAD SEWD THROUGH AT LEAST
   15Z...RESULTING IN EXPANSION OF AREA OF 2-3 INCH/HOUR RAIN RATES IN
   HEAVIEST CORES.  SHORTER-LIVED EPISODE OF SIMILAR RATES IS LIKELY AT
   ANY GIVEN LOCATION AFFECTED BY NEARBY BAND OF TSTMS MOVING EWD ABOUT
   20 KT ACROSS OZARKS OF S-CENTRAL MO AND EXTREME NRN AR.
   
   FAVORABLE CAPE AND LIKELIHOOD OF DENSE PRECIP LOADING ALSO MAY
   SUPPORT LOCALIZED POTENTIAL FOR DAMAGING WET DOWNBURSTS...BUT
   PRIMARY THREAT APPEARS TO BE FROM HEAVY RAIN.
   
   INITIALLY SEPARATE/MESOBETA-SCALE MULTICELLULAR TSTM COMPLEXES HAVE
   DEVELOPED OVER PORTIONS NERN AR--
   1. BAND OF TSTMS LOCATED BETWEEN SGT-ARG..EXPANDING IN COVERAGE AND
   MOVING SEWD ABOUT 20 KT...AND
   2. SOMEWHAT LESS-INTENSE BUT WELL-DEFINED CLUSTER INITIALLY FROM MEM
   AREA NNWWD TOWARD JBR AND NWD TO JUST S OF MO BOOT-HEEL.  CELLS IN
   THIS COMPLEX ARE MOVING SSEWD...BUT OVERALL CLUSTER IS BACKBUILDING
   SWWD TOWARD POTENTIAL MERGER ZONE WITH WRN COMPLEX.
   
   PRIND MERGER WILL OCCUR THROUGH 14Z FROM PORTIONS POINSETT/CROSS
   COUNTIES SSEWD OVER DELTA ADJACENT TO NRN PORTIONS MS/AR BORDER. 
   MEANWHILE MO/AR BORDER-AREA BANDS WILL PROCEED EWD ACROSS UNO AREA. 
   VERY MOISTURE-RICH ENVIRONMENT IS EVIDENT...BASED ON 12Z SGF RAOB
   THAT SAMPLED UPSTREAM 850-MB TRAJECTORIES...YIELDING PW BETWEEN
   2-2.25 INCHES...MEAN MIXING RATIO NEAR 19 G/KG AND MUCAPE OVER 4000
   J/KG.  PW APPEARS SOMEWHAT UNDER-REPRESENTED IN OBJECTIVE/RUC-BASED
   MESOANALYSES OVER SRN MO BASED ON THAT RAOB...BUT APPEARS REASONABLE
   FARTHER SE OVER ERN AR.
   
   ..EDWARDS.. 08/18/2011
   
   
   ATTN...WFO...PAH...MEG...JAN...LZK...SGF...
   
   LAT...LON   34479109 35489161 36639276 37129295 37089179 36899077
               35959033 35278998 34588990 33959001 33889071 34179110
               34479109