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Fox News Weather Center

Cooldown to Invade Midwest, Northeast This Week

After a period of above-average temperatures dominated most of the Midwest and Northeast last week, a complete reversal in the weather pattern will move in this week.

This weather pattern will move across the area after a period of rain and severe storms impact the mid-Atlantic on Monday.

According to AccuWeather.com Long Range Expert Paul Pastelok, a southward dip in the jet stream will develop and will be centered across the Great Lakes much of the time during the latter part of the month.

The jet stream is a fast river of air high above the ground, around the altitude where planes fly, that often marks the dividing line between chilly air to its north and warm air to its south.

The upper-level low associated with this surge of cool air will stall across Ontario for the week. This will send waves of cool air from the Midwest to the Northeast into the weekend.

According to AccuWeather.com Senior Meteorologist Matt Rinde, "The 5- to 10-degree F above-average temperatures will turn the other direction averaging 5-10 degrees below average for the next 7-10 days."

High temperatures across portions of the upper Great Lakes will make it feel more like the end of March than the end of April.

Brisk northwest winds will accompany the cooler air. AccuWeather RealFeel® temperatures will dip into the 30s at times.

"The pattern, which is likely to linger into the first part of May, could also bring a round or two of frost," Pastelok said.

Temperatures are likely to drop below freezing overnight. Gardeners should make sure to cover any plants to prevent frost buildup.

Temperatures will remain above freezing during the overnights to prevent frost along the Interstate-95 corridor from Washington to Boston.

The below-freezing temperatures are not uncommon for this time of the year. Locations from the Upper Midwest to the Northeast tend to observe below-freezing nights into the middle of May.

Scattered showers will also rotate around the low. Some wet snowflakes may mix in across some locations during the overnight hours.

Temperatures can recover to near- or above-average levels in between each wave of cool air, especially over the Ohio Valley and the Interstate-95 corridor. These areas are likely to experience the most sunshine.

High temperatures this week will average in the 30s from northern Michigan to northern Minnesota to the 40s across the remainder of the upper Great Lakes to the 50s across the Northeast, Ohio Valley and the remainder of the Midwest.