MESOSCALE DISCUSSION 0728
   NWS STORM PREDICTION CENTER NORMAN OK
   0658 AM CDT WED MAY 06 2009
   
   AREAS AFFECTED...PORTIONS NRN LA...EXTREME SERN OK...NE
   TX...W-CENTRAL AL...CENTRAL/NRN MS.
   
   CONCERNING...HEAVY RAINFALL 
   
   VALID 061158Z - 061500Z
   
   EACH MCS...INITIALLY ACROSS NERN-CENTRAL MS TO NERN LA...AND
   N-CENTRAL-NERN TX...SHOULD PRODUCE BRIEF BURST OF 2-3 INCH/HOUR RAIN
   RATES AS IT CROSSES DISCUSSION AREA.  HOWEVER...HEAVY RAIN POTENTIAL
   WILL BE EXACERBATED BY TRAILING TSTMS TRAINING ALONG WNW-ESE AXES N
   OF OUTFLOW BOUNDARIES PRODUCED BY LEADING CONVECTIVE COMPLEXES.  1-2
   INCH/HOUR RATES SHOULD BE COMMON IN THIS ACTIVITY AS WELL.  BECAUSE
   OF THEIR SPATIAL OVERLAP...ENTIRE CORRIDOR IS INCLUDED IN THIS
   DISCUSSION.
   
   INITIAL SFC WARM FRONT HAS BEEN OVERTAKEN BY CONVECTION IN MANY
   AREAS...LEAVING COLD POOLS FROM MCS ACTIVITY AS PRIMARY MECHANISM
   FOR FORCING VERY MOIST INFLOW-LAYER PARCELS TO LFC.  SFC DEW POINTS
   70S F WILL REMAIN COMMON AHEAD OF EACH MCS...WITH EFFECTIVE LIFTED
   PARCELS CLOSE ENOUGH TO SFC THAT FORCED ASCENT ALONG LEADING EDGES
   SHOULD PROPEL SFC AIR INTO UPDRAFTS...THEREBY REALIZING FULL DEPTH
   OF MOIST LAYER IN EFFICIENT PRECIP PRODUCTION.  TRAILING ACTIVITY
   WILL BENEFIT FROM MOIST SWLY LLJ...WHICH SHOULD BEGIN TO BLEND
   TOGETHER FROM TWO INITIAL BRANCHES OVER ARKLATEX/...NRN LA AND NRN
   MS REGIONS.  GPS DATA AND MODIFIED MODEL SOUNDINGS EACH INDICATE
   GENERALLY 1.5-1.7 INCH PW UPSTREAM FROM LA/MS AREA AND 15-16 G/KG
   MEAN LOW LEVEL MIXING RATIOS.  THIS MOISTURE -- BENEATH STEEP
   MIDLEVEL LAPSE RATES -- CONTRIBUTES TO MLCAPE 1500-2000 J/KG OVER
   WRN AL RANGING TO OVER 3000 J/KG OVER NE TX.
   
   REF WWS 251-253 AND RELATED MESOSCALE DISCUSSIONS FOR NEAR-TERM SVR
   THREAT WITH THESE SYSTEMS.
   
   ..EDWARDS.. 05/06/2009
   
   
   ATTN...WFO...BMX...MEG...JAN...LZK...SHV...FWD...
   
   LAT...LON   32679077 32819233 31679315 32749549 33249532 33859531
               34189301 33698997 33608777 32418773 32679077