An arm of hot and humid air from the South will extend across the lower Midwest into midweek. The heat will settle over the Ohio Valley on Tuesday and hold over much of Missouri.
Much of the South Central states have been broiling in a late-summer heat wave since last week, where the combination of high temperatures, excessive humidity, sunshine and other conditions resulted in AccuWeather RealFeel® temperatures above 110 F on multiple days.
At St. Louis, high temperatures have been at or above 90 F since the middle of last week. On Monday the temperature reached 100 degrees.
The air began to surge northward into more of the Midwest this past weekend.
In the Northern states, a heat wave is loosely defined as three consecutive days where temperatures reach 90 F or higher.
Most locations over the Ohio Valley states will have two to three days with high temperatures ranging from 85 to 90 degrees, including highs from Sunday, to Tuesday.
RealFeel temperatures peaked just above 100 F in Chicago during the midday hours on Monday, prior to the arrival of a push of cool air from the northern Plains.
In a few locations from Illinois to Arkansas, RealFeel temperatures reached 120 on Monday, which rivaled some of the hottest places over the globe.
The heat is hitting at a time when college and some high school and elementary school students are back in the classroom.
In stark contrast, much cooler air will continue to press eastward across the Northern tier states and will cut the heat off. Within this air mass originating from Canada, temperatures will be slashed by 20 degrees or more from the previous day's high. Temperatures averaged 15 to 20 degrees below normal over portions of Montana and the northern High Plains this past weekend.
The pattern over much of the Ohio Valley states will offer a chance for those who have time off to take in some extended summer weather, which has been rather limited this season.
Temperatures have averaged below normal from St. Louis and Chicago to Detroit, Cincinnati and Pittsburgh since June 1.
The temperature has approached 90 degrees on only a handful of days this summer from Wisconsin and Illinois to Michigan and Ohio. Most of the 90-degree days have been scattered through the season.
The RealFeel temperature hit 105 F at Indianapolis Monday afternoon as the actual temperature approached the 90-degree mark. Pittsburgh is unlikely to hit 90 in the pattern.
According to Senior Meteorologist Dale Mohler, "Since 1990, it was only during the summer of 2004, when the temperature failed to hit 90 degrees at Indianapolis."
"During the last 25 years, Indianapolis has averaged 21 days with temperatures hitting 90 and above."
A spell of very warm weather will also occur in the East at midweek. Temperatures in some neighborhoods from Washington, D.C. to New York City and Boston could reach the 90-degree mark.
Looking ahead to the weekend, a zone of showers and thunderstorms will set up from Texas and the lower Mississippi Valley to Michigan for a time this Labor Day weekend, which could disrupt travel and outdoor activities.
Snow will swing across parts of the central and northern Plains to the Upper Midwest as November ends and December begins.
As millions head home from their Thanksgiving ventures the weather may cause trouble on the roads and at the airports from the southern Appalachians to the central Rockies on Sunday.
The reprieve from heavy rain across southern India will not last with the threat for flooding downpours set to return for the final days of November.
The first widespread ice storm of the season will slowly diminish over parts of the southern and central Plains, but areas of slippery travel will continue into Sunday morning.
An active storm track across northern Europe will bring more wind and rain across Germany into the new week.
Several days of heavy rain will bring the potential for significant flooding from the southern Plains to the middle Mississippi Valley into early next week.