Severe weather across northeastern Illinois and northwestern Indiana
1-minute Mesoscale Domain Sector GOES-19 (GOES-East) Visible images (above) and Infrared Window images (below) included time-matched plots of SPC Storm Reports — which showed thunderstorms that produced several tornadoes, wind gusts as high as 99 mph at Gary in northwest Indiana and 97 mph near Sugar Grove in northeast Illinois, and hail as large as 3.00″ in diameter near Toto in northwest Indiana. The high concentration of damaging winds in the northeast Illinois and northwest Indiana area was only one portion of a derecho event that spanned from eastern Iowa to eastern Kentucky (NWS Chicago | NWS Northern Indiana).
Thunderstorm overshooting tops exhibited infrared brightness temperatures as cold as -80 to -83 C, denoted by violet pixels (above). According to a plot of rawinsonde data from Quad Cities, Illinois (below), those infrared brightness temperatures represented a ~2 km overshoot of the Most Unstable (MU) air parcel’s Equilibrium Level (EL). For an early morning sounding, it showed a very moist and unstable air mass — and the Downdraft CAPE (DCAPE) value of 1194 J/kg highlighted the potential for strong downward transport of momentum to the surface, helping to produce the widespread wind damage that was observed.
