In McHenry County, Ill., northwest of Chicago, funnel clouds were spotted dropping out of the clouds and then retreating again late Sunday morning, said Bob Ellsworth, the assistant director of the county’s emergency management agency. Mr. Ellsworth added that none had touched the ground or caused any damage.
Around the same time, the weather service issued a tornado warning for parts of Kenosha, Racine and Walworth counties in Wisconsin.
Mr. Friedlein said that such strong storms are rare this late in the year because there usually isn’t enough heat from the sun to sustain the thunderstorms. But he said temperatures Sunday are expected to reach into the 60s and 70s, which he said is warm enough to help produce severe weather when it is coupled with winds, which are typically stronger this time of year than in the summer.
“You don’t need temperatures in the 80s and 90s to produce severe weather (because) the strong winds compensate for the lack of heating,” he said. “That sets the stage for what we call wind shear, which may produce tornadoes.”
He also said that the tornadoes this time a year happen more often than people might realize, pointing to a twister that hit the Rockford, Ill., area in November 2010.
NFL games in Cincinnati and Pittsburgh also could be affected by the rough weather.
• Associated Press writer Sophia Tareen in Chicago contributed to this report.