Very warm and humid air will continue to expand northward across the Midwest Sunday and Monday, causing many cities to crack the 90-degree mark for the first time this year.

As the jet stream shifts into central Canada, steamy air will spread from the southern Plains into the Midwest on Sunday. Temperatures across much of the region will soar 5 to 10 degrees above Saturday's highs.

For the first time this year, temperatures will reach or exceed 90 degrees in St. Louis and Indianapolis. Des Moines will flirt with that mark.

Further warming, especially across the Upper Midwest, will send temperatures into the 90s as far north as Minneapolis and Wausau, Wis., on Monday.

The upcoming warmth will challenge record highs in some Midwestern cities and towns. Madison, Wis., is one such location.

Higher humidity will add to the discomfort of the building warmth. Those planning to spend some time outdoors playing sports or doing strenuous work should have extra water handy.

The Midwest will not enjoy a quick end to the steamy conditions. Instead, the air will remain warm and humid into at least midweek.

Story by AccuWeather.com Senior Meteorologist Kristina Pydynowski