ACUS11 KWNS 171043
SWOMCD
SPC MCD 171042=20
ILZ000-WIZ000-IAZ000-171245-

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 https://urldefense.com/v3/__http://www.spc.noaa.gov__;!!DZ3fj= g!6TGQ1dRwhEkmUtPpdWWg2QR4ZzofJIq1M8-TnnkagVZHyglQY9TaLB-C_VuwesuKG1IxNX3Nh= LwR5SmUP-XxvMQG0dQ$ 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=20

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


=3D =3D =3D
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