MESOSCALE DISCUSSION 1087
   NWS STORM PREDICTION CENTER NORMAN OK
   0310 PM CDT SAT JUN 20 2015

   AREAS AFFECTED...CENTRAL/SOUTHERN IOWA...FAR NORTHERN MISSOURI...AND
   FAR WESTERN ILLINOIS

   CONCERNING...SEVERE POTENTIAL...WATCH LIKELY 

   VALID 202010Z - 202215Z

   PROBABILITY OF WATCH ISSUANCE...80 PERCENT

   SUMMARY...ELEVATED CONVECTION CONTINUES OVER EASTERN IOWA...WITH
   ADDITIONAL CONVECTION LIKELY TO DEVELOP ACROSS A COLD FRONT IN
   CENTRAL IOWA.  WITH INCREASING DESTABILIZATION AND CONVECTIVE
   DEVELOPMENT APPEARING LIKELY TO OCCUR...A TORNADO WATCH WILL BE
   ISSUED BY 21Z.

   DISCUSSION...ELEVATED CONVECTION HAS PERSISTED ACROSS EASTERN IOWA
   THROUGHOUT THE DAY...PRODUCING SPORADIC INSTANCES OF MARGINALLY
   SEVERE HAIL AND SUB-SEVERE WIND GUSTS.  TO THE WEST OF THIS
   CONVECTION...STRONG CAPPING AND STRONG INSOLATION HAS ALLOWED FOR A
   STRONGLY UNSTABLE ENVIRONMENT TO DEVELOP WITH 3000-4000 J/KG MLCAPE.
   VEERED SURFACE FLOW IN WESTERN PARTS OF THE DISCUSSION AREA HAVE
   LESSENED THE MAGNITUDE OF LOW-LEVEL SHEAR...BUT 0-3KM STORM RELATIVE
   HELICITY VALUES AROUND 250 M2/S2 INDICATED ON LATEST WSR-88D WIND
   PROFILER AT DMX SUGGESTS THE ENVIRONMENT WILL HAVE SUFFICIENT SHEAR
   FOR STORM ROTATION AND A TORNADO THREAT IN SURFACE BASED STORMS. 
   LATEST HIGH-RESOLUTION MODEL GUIDANCE CONTINUES TO SUGGEST AN
   INCREASE IN SURFACE-BASED CONVECTION ALONG SEWD MOVING COLD FRONT IN
   IOWA...AND DAMAGING WINDS...SIGNIFICANT HAIL...AND TORNADOES ARE ALL
   POSSIBLE AS CONVECTION MATERIALIZES.  A TORNADO WATCH WILL LIKELY BE
   ISSUED BY 21Z.

   ..COOK/GUYER.. 06/20/2015


   ATTN...WFO...ILX...LSX...DVN...DMX...EAX...OAX...

   LAT...LON   42209337 41809446 41499510 40869548 40449522 40129445
               39809299 39709147 39819040 40328984 41089003 41729053
               42099129 42259204 42209337