'Unusual' storm to bring cool, wet weather to Pacific Northwest

Although warmth is already off to the races across much of the northwestern United States, even more heat is in store ahead of an unusual storm and cooler weather to end the week.

Heat began to soar on Thursday and a handful of locations recorded some firsts for the year. The mercury in Portland, Oregon, topped out at 91 F - the city's first reading of 90 degrees or greater of 2020. Typically, the city records its first 90-plus degree day in mid-June. Farther east, Spokane, Washington, recorded its first 80-plus degree day of the year on Thursday.

The mercury will continue to rise across the region on Saturday.

"It will be across the interior Northwest where the heat really cranks up with records in jeopardy of falling," AccuWeather Meteorologist Renee Duff said.

Temperatures soared nearly 20 degrees above normal, into the middle 90s in Boise, Idaho, on Friday, coming close to the long-standing daily record high of 100 last reached in 1897.

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As the interior continues to heat up into the weekend, the hottest days will be in the rearview mirror for costal areas as a storm system begins to sweep from south to north along the Pacific Northwest coast.

"The path of this system is a bit unusual, especially for late May," AccuWeather Senior Meteorologist and western U.S. blogger Brian Thompson said. "One thing that is clear is that the system will help erase the heat across much of the West and get temperatures back closer to average heading into the end of the month and the beginning of June."

Not only will this system spell heat relief for many, it will also usher in some much-needed rain to portions of California, Oregon and Washington.

"Beneficial rainfall is expected to target drought-stricken Northern California and the Pacific Northwest as the system comes ashore this weekend," AccuWeather Meteorologist Tyler Roys said.

Rain first began across Northern California on Friday night and continued to spread northward into the Pacific Northwest early Saturday. The storm is forecast to quickly strengthen over the area on Saturday, with periods of heavy rain expected to fall over western Oregon and Washington during the afternoon and evening.

Although the parched soils across the area will welcome any rainfall, localized flash flooding can develop under the heaviest downpours where soil infiltration is overwhelmed.

Due in part to very warm conditions east of the Cascades and cooler air in the upper levels of the atmosphere, the threat for severe weather will ramp up Saturday afternoon for portions of the Northwest.

These severe thunderstorms will be rather scattered in nature but will likely bring hail, flooding downpours, damaging winds and even an isolated tornado or two to portions of Oregon, Washington, Idaho and Montana through Saturday evening.

An AccuWeather Local StormMax™ of 80 mph wind gusts can occur in the strongest storms.

The center of the storm system will continue to lift northward into British Columbia, Canada, late Saturday into Sunday.

Much of the rain south of the Canadian border will come to an end overnight Saturday, but there will still be a few areas in northern Washington, Idaho and western Montana that will have some rain continue into the day on Sunday.

A widespread 1-2 inches of rainfall is anticipated along the coastal Pacific Northwest over the weekend, with locally higher amounts possible, especially in areas where rainfall is enhanced due to upsloping.

While this storm will not come close to fully erasing drought concerns for the area, every drop of rain will help ease the burden, especially as AccuWeather meteorologists are predicting a rather dry, hot summer with an increased likelihood of wildfires.

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