Train of storms to raise flash flood, mudslide risk in northwestern US this week

By Alex Sosnowski, AccuWeather senior meteorologist

April 09, 2018, 11:01:47 AM EDT

A train of storms will affect the northwestern United States with rounds of drenching rain, heavy mountain snow and gusty winds into next week.

While each of the storms is not likely to be exceptionally strong, the cumulative effect may lead to incidents of flash flooding, mudslides in the lower elevations and an increased risk of avalanches in the high country.

The greatest risk of mudslides will be in recent burn scar locations. However, the risk of mudslides will not be limited to burn areas.

Travel disruptions can be expected.

Most of the storms will dip far enough to the south to bring rain and mountain snow to at least part of Northern California.

While only spotty rainfall is likely in the lower elevations east of the Cascades and Sierra Nevada, locally heavy snow is likely in the ranges that make up the northern Rockies.

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The first storm will move onshore during Tuesday. Rain is forecast to arrive nearly simultaneously in western Washington, western Oregon and northwestern California. Motorists should expect wet travel to quickly develop along much of the Interstate 5 corridor in the region.

As Tuesday progresses, snow will develop over the Cascades, northern Sierra Nevada, Blues, Clearwater and Bitterroots.

Snow levels will start off mainly above the passes on Tuesday from Washington to Northern California, but they are forecast to lower as the second storm rolls ashore on Wednesday. Slippery conditions are likely over Snoqualmie Pass, Washington, on Wednesday and Sexton Summit, Oregon, during Wednesday night.

On a positive note, the series of storms will bring additional snow cover to the high country, which then transforms into a sustainable source of water during the warm season.

Most of the storms are not likely to bring rain to Southern California or the deserts in the Southwest.

Portions of Oregon, southern Idaho, Nevada and Northern California are experiencing long-term abnormally dry to moderate drought conditions, according to the United States Drought Monitor. Areas farther south and east are experiencing severe to exceptional drought from this past winter.

The storms will arrive every one to three days and may continue to move in from the Pacific Ocean through the middle of next week.