ACUS11 KWNS 172143
SWOMCD
SPC MCD 172142=20
ILZ000-WIZ000-172345-

Mesoscale Discussion 0480
NWS Storm Prediction Center Norman OK
0442 PM CDT Fri Apr 17 2026

Areas affected...Southern Wisconsin and far northern Illinois

Concerning...Tornado Watch 129...131...

Valid 172142Z - 172345Z

The severe weather threat for Tornado Watch 129, 131 continues.

SUMMARY...Leading supercells across northern Illinois and southern
Wisconsin will likely pose a tornado (possibly significant) and very
large hail threat as they move downstream over the next 1-2 hours.

DISCUSSION...A pair of leading supercells continues to precede a
broken line of storms along the IL/WI border. Regional radar imagery
continues to indicate that these cells are rather intense with a
three-body scatter spike, a bounded weak echo region, and a recent
3-inch hail report noted with the southern storm. An improving
downstream convective environment is noted in recent observations
and analyses (0-1 km SRH values remain between 200-250 m2/s2 per the
KMKX VWP, and STP values have recently increased to 2-3 per recent mesoanalysis). Additionally, the southern storm will also likely
propagate along a subtle surface theta-e gradient draped across
northern IL to southern WI. Given these trends and the presence of a well-established updraft/mesocyclone with the southern cell, the
potential for very large hail (likely in excess of 2 inches) and
strong tornadoes will likely persist for the next couple of hours
downstream into southeast WI and far northern IL.

..Moore.. 04/17/2026

...Please see https://urldefense.com/v3/__http://www.spc.noaa.gov__;!!DZ3fj= g!9feEzK9nOQKCbzf1RHjIZ1kzfTTsExboMm05oZJ_XRSYfS_lP7-ulpbjcVWQfTdas6Us5FWKZ= Kt1szg9Kzo8X1v9OcA$ for graphic product...

ATTN...WFO...LOT...MKX...DVN...

LAT...LON 42138771 42158906 42268948 42378957 42608965 42798955
42968903 43188791 43108770 42848764 42588767 42138771=20

MOST PROBABLE PEAK TORNADO INTENSITY...140-170 MPH
MOST PROBABLE PEAK WIND GUST...55-70 MPH
MOST PROBABLE PEAK HAIL SIZE...2.75-4.25 IN


=3D =3D =3D
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