Temperatures to plummet as storm brings rain and snow to Northwest

 By Jessica Storm, AccuWeather Meteorologist

Updated Apr. 4, 2021 2:29 PM EDT

Generally mild and dry conditions persisted this past week and into the weekend in the Northwest. The quiet conditions will not last much longer, however, as the region is set to be chilled by cooler air as well as snow and rain showers from a storm moving into the region to end the weekend and start out the upcoming week.

A majority of the Northwest has been experiencing near-average or above-average temperatures over the past few days. Seattle’s high on Friday was 57 degrees Fahrenheit, which is around normal for early April. Temperatures rose Saturday, bumping slightly above normal at 63 F. This warmth won’t last for long though as high temperatures will dive to below normal to near 50 F on Easter Sunday, and showers are expected blossom across the city.

Farther south, conditions have also heated up to above-normal levels over the past few days. Portland ran about 5 degrees above normal on Friday with a high temperature in the mid-60s. On Saturday, high temperatures warmed to 5 degrees above Friday's temperatures. Temperatures are expected to dip below average into the mid-50s on Sunday.

“Many locales across eastern Washington, Oregon, Idaho, Montana and Wyoming will bask in record-challenging warmth on Sunday, however, a storm set to barrel into the Pacific Northwest late this weekend will send temperatures crashing down some 20-30 degrees by early this week,” AccuWeather Meteorologist Brandon Buckingham said.

Temperatures across the interior Northwest have been the most impressive, generally reaching about 10-15 degrees above normal and even breaking records late this past week. For example, the National Weather Service office in Missoula, Montana, recorded 72 degrees on Thursday, breaking the 1966 record by 1 degree.

Boise, Idaho, soared dramatically to the mid-70s both Thursday and Friday, around 15 degrees above normal. Boise hit a toasty 78 on Saturday, which approached the 1987 record high of 79 and put the city at almost 20 degrees above normal. The harder they fall though as another dramatic shift is in store for Boise on Monday, bringing high temperatures down to the lower 50s as showers begin to move in.

“Places like Bozeman and Billings, Montana climbed comfortably into the 70s on Saturday, but temperatures are expected to plummet enough to bring snow back into the forecast by Monday night as the storm moves overhead,” Buckingham said.

The jet stream is diving south, and the storm is expected to move southeastward into the region on Easter Sunday.

Snow levels in the Cascades can drop from 4,500-5,500 feet to 2,000-4,000 feet on Easter, before rising again to around 3,000-5,000 feet on Monday. Snow accumulations of 3-6 inches are possible across the Cascades, with locally higher amounts possible, especially above 5,000 feet. There can be a coating to a few inches between 2,000-5,000 feet.

The storm will then begin moving into Oregon, Idaho and Montana on Sunday, producing snow accumulations of 6-12 inches across the mountainous terrain of Idaho and western Montana, with locally higher amounts possible, especially above 5,000 feet. Snow is expected to continue Monday night and begin to wind down during the day on Tuesday.

“Below-average precipitation was observed across a majority of the Northwest during the month of March, so although the rain and mountain snow may come as a nuisance to some, it will actually prove to be beneficial overall,” Buckingham said.

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Bozeman’s March 2021 precipitation totaled 0.37 of an inch, less than 40% of its average March precipitation. Missoula recorded even less, 0.28 of an inch of precipitation in March, which isn’t even 30% of what the city usually receives during that month. Several other cities, such as Seattle, Boise and Medford, Oregon, also underachieved this past March in terms of wetness.

Despite this benefit though, this nuisance storm can cause travel disruptions and slippery roads across the higher terrain, such as Snoqualmie Pass and Stevens Pass, as snow levels fall. With the recent high temperatures, however, snow is more likely to accumulate in the mountains and on grassy surfaces rather than paved surfaces.

“Dry conditions are slated to return to the Pacific Northwest late Monday into Tuesday as an area of high pressure expands into the region,” Buckingham said. The remainder of the Northwest can expect the storm to come to an end by the end of the day on Wednesday, according to Buckingham. From Wednesday onward, any wet weather will likely be limited to the Pacific Northwest through the remainder of the week.

Late Tuesday, the storm will depart toward the center of the country and could bring more precipitation to the Plains.

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