No further changes to the threat level were made, although the Enhanced risk was significantly expanded late on April 8 to include portions of the southern Great Lakes, lower Ohio Valley, Ozark Plateau, and Arklatex region.

A weaker disturbance pushed from the Ozarks into the Northeast United States, acting to strengthen southwesterly winds aloft across the risk area.

At the surface, a weak area of low pressure initially centered over northeastern Kansas early on April 9 progressed steadily northeast while intensifying, reaching the trisection of Iowa, Wisconsin, and Illinois by late that evening.

Modest surface heating ahead of the cold front allowed mid-level CAPE values to reach 1,000–1,500 J/kg, and a mass of rich moisture transported northward from the Gulf of Mexico pushed dewpoints into the lower 60s °F across the Enhanced risk area.

[5] At 1:50 p.m. CDT (18:50 UTC), the SPC issued a tornado watch for northern and central Illinois, far northwestern Indiana, far southern Wisconsin, and portions of Lake Michigan.

[7] Isolated shower activity had already begun forming across the region just prior to the issuance of watch,[8] eventually growing into a line of strong to severe thunderstorms, including supercells.

[43] The tornado became large and violent as it struck a semi-rural subdivision west of Rochelle, where some ground scouring occurred and large, anchor-bolted homes were swept away, though close inspection revealed that some of the washers were missing from the anchor bolts, and that low-lying shrubbery and vehicles near the homes was left mostly intact, preventing a higher rating.