Severe thunderstorms produce tornadoes, large hail and damaging winds from northern Wisconsin to the Chicago area
1-minute Mesoscale Domain Sector GOES-19 (GOES-East) Visible and Infrared Window images (above) included time-matched plots of SPC Storm Reports — most notably the EF3-rated tornado that moved through the Appleton/Menasha area in northeastern Wisconsin, beginning around 1656 UTC — produced by clusters of thunderstorms on 27 July 2026. Very large hail also occurred in Wisconsin with these storms, including a few reports of 3.00 inches in diameter (and one report of 4.50 inches in diameter, which did not get plotted). Separate thunderstorms also produced large hail, damaging winds and a few tornadoes in the Chicago area.
1-minute GOES-19 Visible and Infrared Window images with an overlay of surface fronts (below) depicted the presence of a surface trough / developing warm front across eastern Wisconsin — the severe thunderstorms were moving southward near or just east of that surface boundary.
A closer look centered near Appleton, METAR identifier KATW (below) showed very high dew points across that area, with KATW reporting a dew point of 81 F at 1545 UTC (about an hour before the tornado). As the parent thunderstorm was approaching from the north, pulses of overshooting tops exhibited infrared brightness temperatures as cold as -75 to -78 C (brighter white pixels embedded within dark black regions).
According to a plot of rawinsonde data from Green Bay (below), infrared brightness temperatures of -75 to -78 C represented a significant overshoot of the Most Unstable (MU) air parcel’s Equilibrium Level (EL). The sounding also portrayed a very unstable atmosphere having a CAPE value of 4770 J/kg and a Lifted Index of -12 C.
Also of note was the Total Precipitable Water (PW) value of 2.12 inches — according to the SPC Sounding Climatology site, this was a record high PW value for all 27 July 1200 UTC soundings at Green Bay (below).
