Tornadoes (including the Appleton/Menasha EF3), 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 — airport METAR identifier KATW (below) showed very high dew points across that area, with KATW reporting a dew point of 81 F at 1545 UTC (surface report plot), 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 MUCAPE 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).
===== 29 July Update =====
In toggle between before/after (13 July vs 29 July) Landsat-8 Natural Color RGB images as visualized using RealEarth (above), a faint signature of the tornado damage path (a transition from green shades to tan shades, due to tree/vegetation damage and an increase of structural debris on the ground) could be seen in the vicinity of Appleton, Fox Crossing and Menasha on 29 July.
Similarly, an image slider comparison between Sentinel-2 Optimized Natural Color RGB images on 13 July vs 28 July is shown below — which provided a better view of the vegetation damage swath (most notably near the bottom-center portion of the 28 July image, which is the Menasha area).