(CNN) -- The Upper Midwest is about to get three days of September -- in July.
An unseasonal invasion of cool Canadian air could put lows in the 40s -- about 10 to 15 degrees below normal -- in parts of North Dakota, Minnesota, Wisconsin and Michigan into Wednesday.
Chicago, too, will be wondering what month it is, with lows in the 50s and highs Tuesday and Wednesday in the low 70s.
The reason: Last week's Typhoon Neoguri created some ripples in the jet stream, causing it to dip farther south than it normally does this time of year.
"It's not weird to get a dip in the jet stream, but it is weird to get it in July, dipping this far south," CNN meteorologist Jennifer Gray said. "So we are getting those cooler than normal temperatures across the Great Lakes region."
• Duluth, Minnesota, will see lows in the upper 40s Tuesday and Wednesday, with highs in the upper 60s and low 70s. Monday's expected high, 59, is well below the July normal of 75.
• Marquette, Michigan, also will see lows in the upper 40s Tuesday and Wednesday, with highs in the low 60s Monday and Tuesday. The average high for this time of year is 77.
• Grand Forks, North Dakota, will see lows in the upper 40s or lower 50s Tuesday and Wednesday. Monday's high will be around 67 -- a departure from the July normal in the low 80s.
Meanwhile, the East will be getting drenched. Three inches of rain are possible in the Mid-Atlantic and the Northeast from Monday to Wednesday.
Storms on Monday could be severe in parts of the country, including much of the East Coast from Virginia to the north, as well as Tennessee, Kentucky, Indiana, Ohio and West Virginia. Damaging wind and heavy rain are possible.
By Tuesday, the strongest storms should be confined to the Mid-Atlantic, and they'll be mostly along the coast Wednesday.
CNN"s Sherri Pugh contributed to this report.