Dramatic cooldown to replace stifling heat in northwestern US

Following record-challenging heat in the Pacific Northwest early this week, a significant cooldown is set to follow by late week.

An expansive area of high pressure bulging northward to the Canadian border was responsible for the surge of oppressively hot air at midweek.

While temperatures of 10- to 20-degrees Fahrenheit above normal will linger through Thursday over the interior Northwest, the cooldown will waste no time near the coast.

“After a few weeks of generally warm and dry weather, a pattern change will bring much cooler and wetter weather to the West,” said AccuWeather Meteorologist Ryan Adamson.

The increase in cloud cover and the arrival of precipitation will signal an abrupt end to the extreme heat.

“Temperatures will be 10 to as much as 25 degrees lower between the highs that occurred on Tuesday and the forecast highs by Friday and Saturday,” Adamson added.

In Seattle and Portland, Oregon, high temperatures in the 80s will be replaced by temperatures some 5-10 degrees below normal from late week into the upcoming weekend. In fact, temperatures may struggle to reach the lower 60s on the coolest days.

Farther inland, temperatures in Great Falls and Spokane, Washington, will also dip into the 60s by the weekend and replace near-record heat with unseasonably chilly air.

As the major storm system plows eastward into the northern Rockies during Thursday and Friday, severe thunderstorms capable of producing damaging wind gusts and torrential downpours may rattle residents from Cut Bank, Montana, to Missoula, Helena and Great Falls, Montana.

The drastic change in the weather pattern will have residents not only scrambling for jackets and umbrellas, but also on alert for potential power outages and property damage from the storms.

For areas west of the Cascades, a brief break in the rain on Thursday night will quickly be erased as showers resume by Friday afternoon.

Adamson added that an even colder pocket of air will swirl across the Pacific Northwest this weekend, with the greatest effects being felt from Oregon into Northern California.

“The air will be cold enough for snow to be seen over the mountains," Adamson said. "Hikers and outdoor enthusiasts will need to be prepared for a brief return to winterlike conditions in the highest elevations."

The large vortex of chilly and unsettled conditions will slowly trek eastward through the northern Rockies by early next week, allowing drier conditions to return to the Northwest.

How intense the storm system becomes and its exact track can determine where and how much rain and snow falls.

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