ACUS11 KWNS 172351
SWOMCD
SPC MCD 172350=20
INZ000-ILZ000-180145-

Mesoscale Discussion 1171
NWS Storm Prediction Center Norman OK
0650 PM CDT Wed Jun 17 2026

Areas affected...Parts of south-central Illinois into southwest
Indiana

Concerning...Tornado Watch 342...344...

Valid 172350Z - 180145Z

The severe weather threat for Tornado Watch 342, 344 continues.

SUMMARY...Large hail, damaging winds, and the potential for a few
tornadoes will continue spreading east-southeastward this evening --
within Tornado Watches 342/344.

DISCUSSION...A couple supercells are tracking east-southeastward
along the southern flank of a larger convective cluster in east-central/southeast IL -- with additional
development/intensification farther west in south-central IL.
Despite the presence of very strong low/deep-layer flow/shear
sampled by the IND VWP (60 kt low-level jet and 650-700 m2/s2 0-1 km
SRH), these storms are tracking through a corridor of convectively
processed air from earlier storms. However, the strong low-level
mass response accompanying an approaching midlevel wave may support
additional boundary-layer recovery toward the inflow of these storms
during the next few hours. If this can occur, the robust low-level shear/streamwise vorticity will support a few tornadoes (some of
which could be strong-intense) with any longer-lived supercells.
Very large hail and severe wind gusts (75+ mph) will also be
possible with these storms as they continue east-southeastward.

..Weinman.. 06/17/2026

...Please see https://urldefense.com/v3/__http://www.spc.noaa.gov__;!!DZ3fj= g!6UzEaPWvF6Fl_GbNI0OR0kDKyc8ApVq54t-WzFF73LlKfzHlNAmOfIf3O7Smc5pMjB3ocmfXh= pwi8A3MXY_UZmT6-zg$ for graphic product...

ATTN...WFO...IND...ILX...LSX...

LAT...LON 39128678 38888686 38788721 38928769 39158879 39188973
39368996 39648986 39718954 39718833 39598770 39458719
39338688 39128678=20

MOST PROBABLE PEAK TORNADO INTENSITY...120-145 MPH
MOST PROBABLE PEAK WIND GUST...65-80 MPH
MOST PROBABLE PEAK HAIL SIZE...2.00-3.50 IN


=3D =3D =3D
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