The first part of this week will feel more like September than the middle of July, typically the hottest time of year, throughout the Midwest.
The unseasonably cool air is arriving via a piece of the polar vortex.
That does not mean that kids across the Midwest will be trading their swimming gear for sled and skis.
As AccuWeather.com Senior Meteorologist Alex Sosnowski first reported last week, this is a summertime version of the polar vortex that has broken off from the Arctic and is dropping southward.
The advancing cooler air will help trigger severe thunderstorms across the Ohio and Tennessee valleys Sunday through Monday.
Many residents will opt for jackets for the first part of the week as temperatures will be 10 to 20 degrees below normal for this time of year, stated AccuWeather.com Meteorologist Steve Travis.
Typical mid-July highs range from 77 F in Marquette, Michigan, to the mid-80s in Minneapolis, Chicago and Cincinnati to 89 F in St. Louis.
Monday will be the coolest day of the week in and around Minnesota with widespread highs in the 60s. Temperatures will even fail to rise out of the 50s in the vicinity of Lake Superior, including in Marquette, Michigan.
Monday's highs will actually be closer to the day's average low temperatures in Minneapolis and Duluth. A breeze will create even lower AccuWeather.com RealFeel® temperatures.
"Overnight lows will also feel quite chilly with many areas of the Upper Midwest in the lower 50s. Some places will even drop into the 40s," Travis stated.
Baseball fans watching Monday's Home Run Derby and Tuesday's All-Star Game at Target Field in Minneapolis may feel like they should be tailgating for a Minnesota Vikings football game in September.
The core of the cool air will spread across the Great Lakes Tuesday through Wednesday, holding temperatures to the 60s and lower 70s.
The cool weather through Wednesday will be accompanied by building clouds, daily showers and the danger of waterspouts on the Great Lakes.
Monday will be the most active day with a couple of small hail-producing thunderstorms also rumbling from northeastern Minnesota to northern Michigan.
For the warm weather-loving residents who are not ready for September to start, Travis has good news. "Temperatures will gradually warm up toward the end of the week."
While the Northeast's I-95 corridor will turn less humid later in the week, the cool blast will lose its punch prior to pressing that far east as the piece of the polar vortex lifts back to the Arctic.