ACUS11 KWNS 171544
SWOMCD
SPC MCD 171543=20
INZ000-ILZ000-171745-

Mesoscale Discussion 1163
NWS Storm Prediction Center Norman OK
1043 AM CDT Wed Jun 17 2026

Areas affected...central Illinois into western Indiana

Concerning...Tornado Watch 340...

Valid 171543Z - 171745Z

The severe weather threat for Tornado Watch 340 continues.

SUMMARY...Damaging wind and tornado potential continues within
WW340.

DISCUSSION...Several broken thunderstorm clusters continue across
south-central Illinois. The leading line of this convection appears
to still be tied to the stronger cold pool/outflow producing gusts
60-65 mph in the last hour. The air mass across southern Illinois
into Indiana is only marginally unstable, however, temperatures are
warming into the mid to upper 70s F under mostly sunny skies with
dew points in the mid to upper 60s F. Additionally, the low level
jet axis (as shown in SPC Mesoanalysis and sampled from VAD profiles
from LSX and ILX) still extends into central/southern Illinois with
ample deep layer shear for organization, which may overcome the more
marginal air mass. Hi-res CAM guidance suggests this cluster will
weaken with time into eastern Illinois. Though guidance suggests
weakening, the continued low-level jet influence and heating ahead
of the line leads to low confidence in exactly when severe potential
will decrease downstream. Trends will be monitored, with potential
for a watch to be issued downstream of WW340.

Within WW340, tornado potential continues along the southern edge of
the current ongoing cluster. Here, more favorable low-level shear
may support a tornado or two within more discrete cells.

..Thornton/Hart.. 06/17/2026

...Please see https://urldefense.com/v3/__http://www.spc.noaa.gov__;!!DZ3fj= g!7969pQpWdVgHkwZ44JX4PBpuHUrV0k9v5hV47vrcJCR9J1Lw0zabSxI5xMCJJZ2KwJfmzF-GR= 1L_6BLq63n3YylwmrE$ for graphic product...

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

LAT...LON 39649038 40128976 40508902 40528786 40078711 39678708
39268703 38808724 38798920 39219031 39649038=20

MOST PROBABLE PEAK TORNADO INTENSITY...100-125 MPH
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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