Though June averaged below-normal in temperature, the month ended with the arrival of tropical air. Summertime heat is forecast to persist the rest of the workweek, extending a spell of above-normal readings. Monday’s high of 89 degrees at O’Hare airport marked the ninth straight day with temps at or above normal, while Midway airport recorded its fifth 90-degree day of the season. The Chicago area is expected to stay on the warm side of a front extending across the upper Midwest. Daytime readings are to hover near 90 through at least Thursday. The front to our north will act as a focus for periodic thunderstorm development. Satellite imagery late Monday showed a large storm complex over southern Minnesota and northern Iowa. Some storms may migrate into the metro area by Tuesday.