Dramatic cooldown across Rockies, Midwest to arrive just in time for fall

Residents from parts of the Rockies to Plains states may soon be dealing with a case of weather whiplash, AccuWeather meteorologists say. A stretch of unseasonable warmth that brought record high temperatures in the 90s in spots this past week will be a distant memory by early week as a period of much cooler weather unfolds.

The pattern change will arrive just in the nick of time for the change of seasons, as fall will officially begin on Wednesday at 2:21 p.m. CDT. However, residents still have another few days of summer heat to endure.

This September has been a warm month across the Rockies and central Plains, with temperature departures generally running 4 to 6 degrees above normal through Sept. 16. It has also been a warm month in the northern Plains and Upper Midwest, although departures have not been quite as extreme.

"Temperatures across the Upper Midwest and northern Plains have been running 1 to 3 degrees above normal this month," said AccuWeather Meteorologist Matt Benz.

Through Sunday, this warmth will continue and add to the above-normal departures. Before a change to lower temperatures, a few cities may even be close to rewriting the record books.

"Temperatures could be near record territory ahead of a cold front with places like Bismarck, North Dakota and International Falls, Minnesota, approaching record highs by Sunday afternoon," said Benz.

In Bismarck, Sunday's forecast high temperature is 82 degrees. While this is likely to fall several degrees short of the record of 94 degrees set in 1972, the normal high on Sept. 19 is 72 degrees.

International Falls will have a slightly better chance of at least tying a record on Sunday. The expected high of 84 degrees is just behind the record of 86 degrees from 1914 and 1970. These temperatures are a far cry from the typical high of 65 degrees on Sept. 19.

Temperatures could exceed 90 degrees in parts of South Dakota. However, some record highs there are near 100 degrees on Sunday, so new records are not expected.

By late Sunday and Monday, a strong cold front is expected to move into the central Rockies and Plains. Ahead of the front, warm and humid air may spark some gusty thunderstorms. Behind the front, a much cooler air mass will rush into the region. Some locations in the Rockies are forecast to receive their first snowfall of the season.

"Many folks may experience seasonal whiplash later this weekend and into next week as a decidedly fall-like storm sweeps across the region," said Benz.

After a high of 76 degrees on Sunday, Casper, Wyoming will struggle to get out of the 50s on Monday. Normally, a high of 74 degrees is observed during this time in September in Casper.

Farther south, Salt Lake City will have a similar fate: falling from 74 degrees on Sunday to 64 degrees on Monday. A typical high in Salt Lake City is 79 degrees.

In Denver, temperatures will shift from near 90 this weekend to the low 70s and upper 60s on Monday and Tuesday. An average high temperature for this time of year in the Mile High City is 80 F.

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On Thursday, temperatures tied the record high of 97 last set in 2000 in Pueblo, Colorado, while North Platte, Nebraska, set a record high of 96, breaking the daily record of 94 which was set more than a century ago in 1891. Both cities are forecast to have highs near 70 F by next Tuesday.

This front and cooler air will continue to move eastward on Tuesday. The eastern Dakotas, Minnesota and Iowa will feel the change on this day. For example, Minneapolis will plunge from 74 degrees on Monday to just 66 degrees on Tuesday. In addition, clouds and a breeze will make the temperature feel even lower. With a normal high of 72 degrees, temperatures will go from well above to well below average and low temperatures will follow a similar trend.

"The forecast low in Minneapolis is 47 degrees on Tuesday night which, would approach the lowest temperature since May 29 when the mercury dropped to 42," said Benz.

A morning temperature around 53 degrees is more typical in the Twin Cities.

Temperatures will rise closer to normal by the middle and latter parts of the upcoming week, but sweltering heat appears to be in the rearview mirror after this weekend.

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