Pacific Northwest to face increased flood threat as stormy pattern continues

 By Brandon Buckingham, AccuWeather Meteorologist

Updated Feb. 21, 2021 11:47 AM EST

Amid a persistently cold and wet pattern across the Northwest throughout the month of February, a changing weather regime will bring along another influx of moisture into the region. This time however, the moisture source will originate from the tropical Pacific, leading to a few key differences.

The consistently wet and unsettled pattern first targeted Oregon and Northern California Friday night as a quick-hitting storm system slammed into the coastline. Rumbles of thunder were even heard in places like Crescent City, California as the storm pressed inland.

Water vapor imagery along the West coast showing the arrival of a storm system in Oregon and Northern California Friday night (GOES 16)

The storm continued on a quick eastward pace through the day on Saturday, largely coming to an end along the Oregon and California coasts by midday. Rain and snow showers continued to progress inland into the Great Basin and central Rockies, leading to some tricky travel conditions.

The main event that will be responsible for a more noticeable pattern change across the Northwest, and a majority of the United States in the coming days, began pushing onshore Sunday morning.

Because of the higher snow levels expected with the upcoming storm system Sunday and Monday, this will likely lead to an increased flood threat as a result of both falling rain and melting snow.

During the day on Sunday, a steady stream of rainfall is expected along the Interstate-5 corridor in western Washington and Oregon as the storm makes its final approach. Places like Seattle and Tacoma, Washington, as well as Portland and Salem, Oregon can expect rounds of wet weather as a result.

Into Sunday night, a steadier, heavier rain is expected to begin to increase the flood threat across the region. Because of the expected high snow levels, runoff from the Cascade Mountains will act to further increase river levels in the area. Western Washington is expected to take the brunt of the precipitation overnight Sunday, with lesser amounts farther south in western Oregon.

This may lead to travel issues for the Monday morning commute in many locales along and west of the Cascade Mountains. There will be a potential for mudslides, which could render some roads impassable for a time.

These threats will translate southward during the day on Monday, so places like Portland and Salem, Oregon can expect periods of steady rainfall.

While the bulk of the wet weather will come between Sunday and Monday, there will likely be lingering rain and snow showers into the day on Tuesday as well. Snow levels are expected to drop down closer to pass levels, which may further complicate travel conditions.

A break in the stormy pattern is slated for Wednesday, however it likely will not last long, as the next storm system to approach the Pacific Northwest will arrive on Thursday.

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