CHICAGO (CBS) — Get ready for a day that would even seem hot by the standards of mid-July.

While the calendar reads September and the Halloween merchandise is already going on the shelves in some stores, the forecast high on Friday will be a sweltering 96 degrees, with heat indices that could exceed 100.

In some places, the raw air temperature might even flirt with 100.

A heat advisory is in effect until 7 p.m. for some downstate counties starting not too far south of the Chicago area, including Kankakee, Livingston, Ford and Iroquois counties. In those areas, the National Weather Service warns that heat indices could top out at 105 degrees.

The Weather Service advises rescheduling any strenuous outdoor activities to the evening or early morning hours, wearing light and loose-fitting clothing, drinking plenty of water, and watching for the symptoms of heat stroke and heat exhaustion.

No advisory is in effect for the immediate Chicago area. But if you heard thunderclaps overnight and thought maybe the cold front we’re expecting this weekend had come in early, think again.

As forecast, conditions will be hazy, hot and humid throughout the day. The threat of extreme heat has been enough for officials at Indian Prairie School District 204 in Naperville to close 19 elementary schools that do not have air conditioning on Friday.

But if you’re a fan of the steamy heat of midsummer, enjoy the day, because the next time we see such temperatures may well be next year. On Friday night, that cold front will blow in from the west, and storms will dominate the skies through Saturday as a result.

Come Sunday, it will feel much more like fall, with temperatures only reaching 72 degrees for a high. Come Monday, the high is a mere 69 degrees, with a jacket-worthy overnight low of 56.