A late season heat wave is on the way for the Aurora area. This will be a sharp change from the cool pattern that has dominated most of the summer. The heat looks like it will break by midweek, before rebuilding towards next weekend.
Over much of the summer, a trough has been carved into the eastern United States. This has been reinforced by a jet stream digging into the Midwest from Canada and has kept the area cooler than normal. The National Weather Service shows that O'Hare airport has officially recorded only 7 days at or above 90 degrees this year. By this time last year, there were 42 days at or above 90 degrees in the books! This jet stream will lift north into Canada and an upper level ridge will take its place. A classic summer pattern will then develop as the Bermuda high pressure over the Atlantic shifts westward into the United States. This will turn the winds southwesterly and bring in the heat.
Sunday will see temperatures surge to near 90 degrees as southwest flow begins to kick in. Monday and Tuesday will be the hottest days, with the warmest air aloft moving in as the ridge establishes itself over the area. Temperatures should reach the middle 90's. There will be moderate, but not oppressive levels of humidity. Tuesday will have to be watched as thunderstorms roaming the upper ring of the heat dome may approach the Wisconsin Illinois border. Any cloud debris from this could limit high temperatures a bit.
The bermuda high will begin to break down on Wednesday as the upper level ridge retreats to the west. As a result, a cold front will slide through from the north. This should act to lower temperatures a bit, into the middle to upper 80's. The ridge may build back to the east and introduce more heat by Labor Day weekend.