MESOSCALE DISCUSSION 0580
   NWS STORM PREDICTION CENTER NORMAN OK
   0726 PM CDT MON APR 29 2013
   
   AREAS AFFECTED...PORTIONS IA....ERN NEB.
   
   CONCERNING...SEVERE POTENTIAL...WATCH POSSIBLE 
   
   VALID 300026Z - 300300Z
   
   PROBABILITY OF WATCH ISSUANCE...40 PERCENT
   
   SUMMARY...ISOLATED SVR POTENTIAL EXISTS BEFORE DARK WITH CONVECTION
   OVER PORTIONS CENTRAL/WRN IA.  MORE ORGANIZED THREAT MAY DEVELOP
   LATER THIS EVENING...AFTER ABOUT 02Z...WITH LARGE HAIL AND DAMAGING
   GUSTS POSSIBLE. AREA WILL BE MONITORED FOR CONVECTIVE/ENVIRONMENTAL
   TRENDS SUPPORTING WW ISSUANCE.
   
   DISCUSSION...SFC MESOANALYSIS SHOWS DIFFUSE/WEAKENING WARM FRONT
   EXTENDING NEWD FROM SWRN KS SFC LOW ACROSS SERN NEB AND CENTRAL IA. 
   FRONT HAS LOST MUCH OF ITS THERMAL IDENTITY AMIDST STG DIABATIC SFC
   HEATING ON BOTH SIDES...BUT STILL IS WEAKLY EVIDENT AS SFC WIND
   SHIFT AND ILL-DEFINED THETAE GRADIENT...S OF WHICH SFC DEW POINTS
   REACH MID 50S TO LOW 60S IN SOME AREAS.  AS OF 0015Z...ISOLATED
   SMALL TSTM HAS FORMED WITHIN AREA OF CU...AND EITHER IN OR JUST N OF
   ILL-DEFINED FRONTAL ZONE...OVER PORTIONS CALHOUN/WEBSTER COUNTIES. 
   MODEL FCST SOUNDINGS AND AVBL RAOBS...MODIFIED FOR PROXIMITY 00Z SFC
   OBS...INDICATE AROUND 1000-1500 J/KG MLCAPE ATOP WELL-MIXED SUBCLOUD
   LAYER SUITABLE FOR SUPPORTING STG...POSSIBLY DAMAGING DOWNDRAFTS. 
   SOME CLOCKWISE TURNING OF WIND VECTORS WITH HEIGHT IS APPARENT IN
   LOW-LEVEL FLOW ABOVE SFC...AND 40-50 KT EFFECTIVE SHEAR MAGNITUDES. 
   HOWEVER...DEEP SHEAR IS MORE LIMITED WITH NWD EXTENT BY RELATIVELY
   WEAK MID-UPPER LEVEL FLOW.  
   
   MLCINH SHOULD INCREASE AFTER DARK AS DIABATIC COOLING OFFSETS SFC
   MOIST ADVECTION...AND LLJ STRENGTHENS IN RESPONSE TO CYCLOGENESIS
   OVER NRN PLAINS.  THOUGH THAT LIKELY WILL CONSTITUTE SEPARATE
   CONVECTIVE REGIME OVER THIS GENERAL AREA...SOME CONTINUITY IS
   POSSIBLE FROM ANY SUSTAINED CONVECTION THAT MAY FORM OVER NEXT 3-4
   HOURS.
   
   ..EDWARDS/KERR.. 04/30/2013
   
   
   ATTN...WFO...DVN...ARX...MPX...DMX...EAX...FSD...OAX...
   
   LAT...LON   42199600 42749529 43529422 43239277 42709197 41999217
               41349326 40389635 41119671 42199600