Though this past 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 work week, extending a spell of above normal readings. Monday’s high of 89 degrees at O’Hare airport marked the 9th straight day with temperatures at or above normal, while Midway airport recorded its 5th 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 the 90-degree mark 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 of these storms may migrate into the metro area by Tuesday morning, but storms, possibly severe, are more likely later in the day.