Storm Prediction Center Mesoscale Discussion 1161

   Mesoscale Discussion 1161
   NWS Storm Prediction Center Norman OK
   0542 AM CDT Wed Jun 17 2026

   Areas affected...Central and Eastern Iowa...Northwest Illinois

   Concerning...Severe Thunderstorm Watch 339...

   Valid 171042Z - 171245Z

   The severe weather threat for Severe Thunderstorm Watch 339
   continues.

   SUMMARY...A threat severe wind gusts and isolated large hail will
   continue across central Iowa over the next hour, and is expected to
   increase over eastern Iowa and northwest Illinois as daybreak
   approaches.

   DISCUSSION...A cluster of severe storms is currently located over
   central Iowa, along the eastern edge of an unstable airmass. The RAP
   shows moderate instability over much of western and central Iowa,
   where MUCAPE is currently estimated in the 1000 to 2000 J/kg range.
   As an 850 mb jet strengthens across the mid Missouri Valley early
   this morning, MUCAPE will steadily increase and should reach the
   2000 to 3000 J/kg range around daybreak from central Iowa into
   northwest Illinois. This will provide additional fuel to the ongoing
   convection, helping the storms to become more organized with time.
   The instability combined with a strong wind field (effective shear
   55 to 65 knots) will result in a potential for supercells with
   isolated large hail. Supercells will be embedded in the ongoing line
   segment. The line segment may begin to take on a bowing shape is it
   move across southeast Iowa. This could mean that severe wind gusts
   will become the greatest threat as the line moves across the eastern
   part of weather watch 339. A potential will exist for significant
   wind gusts in excess of 65 knots.

   ..Broyles/Guyer.. 06/17/2026

   ...Please see www.spc.noaa.gov for graphic product...

   ATTN...WFO...LOT...ILX...MKX...DVN...ARX...DMX...

   LAT...LON   40539069 41048984 41698960 42178979 42519041 42689131
               42839236 42919343 42699400 42329428 42039433 41789418
               41389349 40719177 40539069 

   MOST PROBABLE PEAK WIND GUST...65-80 MPH
   MOST PROBABLE PEAK HAIL SIZE...1.00-1.75 IN