Pattern Change Triggers Raw, Chilly Midwest, Northeast, and a Western Heat Wave

 Jonathan Erdman

Published: May 29, 2021

A pattern change has already cooled off the Great Lakes and is spreading into the East and South as increasing heat develops in the Northwest. However, this shift in the weather pattern won't put an end to the persistent storminess in the Plains.

Recently, some locations chalked up their first 90s of the season, including Buffalo, Boston, Chicago, Philadelphia, Raleigh and Atlanta.

Meanwhile, parts of the Northwest had been stubbornly chilly. Areas in the northern Rockies picked up more late-spring snow, adding to the annual task of clearing mountain roads through Glacier National Park.

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But that overall temperature arrangement has changed; The dome of high pressure aloft responsible for the eastern heat is long gone.

By early next week, the jet stream will look much different. It will buckle northward over the Pacific Northwest and subtly sweep southward into the Great Lakes and Northeast.

Forecast weather pattern setting up early in the week of May 31.

It's not a spectacular jet-stream shift that you might see in the winter, but it will lead to a pair of big changes while keeping one thing largely the same.

East, Midwest Cools Down

This pattern change sent northern Minnesota from summerlike warmth to a taste of winter in a matter of hours. After a high of 82 degrees on Tuesday, International Falls, Minnesota, dropped into the 30s with a period of snowfall on Wednesday morning.

Much of the Upper Midwest saw downright chilly and raw conditions on Thursday. With a high of only 39 degrees, Thursday was the coldest day so late in spring in almost 75 years in Marquette, Michigan. Wet snow was reported in at least three locations in Lower Michigan Friday morning.

Daytime highs in New York felt more like late winter than late Spring Friday afternoon.

This weekend, the cooler air will finally make its way down the East Coast.

Rain-cooled highs in the 50s are possible in the Northeast and Mid-Atlantic states Saturday and Sunday.

(MAPS: 10-Day U.S. Forecast Highs and Lows)

While a threat of lingering showers and thunderstorms may still be in play in some areas, highs in the 70s and 80s should be more common in the Southeast Saturday and Sunday. This front will be accompanied by lower humidity and much cooler nights.

Forecast Highs Sunday

Western Heat Wave Ahead

Meanwhile, with the jet stream bulging northward into western Canada, hotter, drier weather will develop in the West during Memorial Day weekend and amplify into a full-blown heat wave next week.

Highs will soar into the triple digits in California's Sacramento Valley by Sunday, could push toward 90 degrees in Portland, Oregon, and 80 degrees in Seattle by Tuesday. By the middle of the week, 90s could surge into eastern Washington and Idaho, threatening daily record highs. A few spots in southern Oregon may rise above the century mark.

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Of course, this is not good news for the ongoing drought in the Pacific Northwest and California. This will likely lead to an increased fire danger next week.

Plains Remain Stormy

One thing that won't change from this jet stream pattern shift into next week is the parade of Plains thunderstorms.

That's because there will be a number of weak disturbances in the atmosphere pivoting out of the Desert Southwest and sliding southward along the east side of the Pacific Northwest ridge to provide just enough energy to ignite thunderstorms.

This doesn't mean all areas in the Plains will see thunderstorms every day.

For instance, the central Plains should largely be dry again Saturday.

However, the High Plains – from Wyoming and western Nebraska to Colorado, western Kansas, New Mexico and western Texas – could see thunderstorms each day through the holiday weekend, and that general thunder threat could inch slowly eastward into the rest of the Plains early next week.

(MAPS: 7-Day U.S. Daily Rain Forecasts)

The Weather Company’s primary journalistic mission is to report on breaking weather news, the environment and the importance of science to our lives. This story does not necessarily represent the position of our parent company, IBM.

The Weather Company’s primary journalistic mission is to report on breaking weather news, the environment and the importance of science to our lives. This story does not necessarily represent the position of our parent company, IBM.