MESOSCALE DISCUSSION 0357
   NWS STORM PREDICTION CENTER NORMAN OK
   0503 PM CDT SAT APR 17 2004
   
   AREAS AFFECTED...PORTIONS NRN IA AND EXTREME SRN MN
   
   CONCERNING...SEVERE THUNDERSTORM POTENTIAL 
   
   VALID 172203Z - 180030Z
   
   RAPID DEVELOPMENT OF SEVERE TSTMS IS POSSIBLE BETWEEN 22Z-00Z IN
   NWRN IA -- ESPECIALLY N OF I-70 BETWEEN SUX-MCW.  RESULTING TSTMS
   THEN SHOULD MOVE/EXPAND EWD WITH DAMAGING HAIL/WIND
   POSSIBLE...PERHAPS A TORNADO EARLY IN SUPERCELL LIFESPAN.  WW MAY BE
   REQUIRED IN NEXT 1-2 HOURS.
   
   SFC MESOANALYSIS SHOWS WARM FRONT E-W ACROSS IA FROM NEAR SUX TO
   JACKSON COUNTY...LIFTING NWD AROUND 15-20 KT TOWARD MN BORDER.
   AIR MASS ALONG AND WITHIN 20 NM N OF WARM FRONT WILL BE MOST
   SUITABLE FOR SEVERE.  IN THAT REGIME HIGHER DEW POINTS ARE ADVECTING
   INTO AREA BUT SFC FLOW REMAINS BACKED...OPTIMIZING SHEAR. 
   PROFILER/VWP DATA N OF FRONT SHOWS 250-450 J/KG SRH IN 0-3 KM
   LAYER...AND 50-60 KT SHEAR THROUGH 6 KM AGL.  ALTHOUGH BOUNDARY
   LAYER FLOW WILL VEER TO SLY WITH FROPA...HODOGRAPHS STILL WILL BE
   FAVORABLE FOR BOTH SUPERCELLS AND EVENTUAL BOW DEVELOPMENT.
   
   MODIFIED RUC SOUNDINGS INDICATE CINH NEARLY GONE OVER NW IA BY
   23Z...CONSISTENT WITH VIS IMAGE TRENDS OF GRADUALLY DEEPENING CU
   ELEMENTS NEAR WARM FRONT.  SFC DEW POINTS ARE LOCALLY ENHANCED OVER
   REGION BY SWATH OF WET GROUND FROM OVERNIGHT MCS...BUT MEAN MIXING
   RATIOS SUPPORT USE OF 61-64 F SFC DEW POINTS OBSERVED AT MOST
   STATIONS AS MOST REPRESENTATIVE LIFTED PARCEL. WITH 8-9 DEG C
   MIDLEVEL LAPSE RATES THIS STILL GENERATES AROUND 3000 J/KG
   MLCAPE...INDICATING EXPLOSIVE UPDRAFTS POSSIBLE ONCE CAP DOES BREAK.
    SOME CONVECTION OVER NRN IA MAY AFFECT AREAS NEAR MN BORDER
   ...PERHAPS AS FAR N AS SRN-MOST MN COUNTIES.
   
   ..EDWARDS.. 04/17/2004
   
   
   ATTN...WFO...ARX...MPX...DMX...FSD...OAX...
   
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