Atmospheric Rivers Target Pacific Northwest With Heavy Rain and Flooding

The storm action is just getting started in the Pacific Northwest. After a blustery and wet weekend, the atmospheric river train is going to continue to unleash across this corner of the country.

More Atmospheric Rivers Taking Aim at the Northwest

The Pacific storm machine will persist throughout British Columbia and portions of Washington state this week before shifting to the south and bringing Oregon and Northern California into the mix. These long plumes of moisture coming up from the Pacific will bring repeated rounds of strong winds, rough seas, and heavy rain.

Forecasters are warning that the persistent rounds of heavy rain will pair with melting snow at the intermediate elevations to raise the risk of runoff and small stream and urban flash flooding. The activity fired up over the weekend in Washington and British Columbia. Thousands were left without power in Seattle when a potent windstorm blew in on Saturday evening.

A brief respite in the conditions on Sunday gave residents the chance to clean up the damage. However, the next storm is already making its way from the coast on Monday. This weather maker will bring yet another round of moisture and winds on Tuesday and into early Wednesday. A third wave is forecast to arrive late Thursday and into Friday.

The latest forecast models predict widespread rain of 2 to 4 inches from late Monday through Friday across the lower elevations of western British Columbia and to the south into the western foothills of Washington's Olympic Peninsula and the Cascades.

Heavier rain totals of 4 to 8 inches are in store for Canada's Coast Mountains, Vancouver Island, and across the lower and intermediate elevations of the Coast Mountains. Projected rainfall rates of 1 to 2 inches per hour during the peak of the storms are prompting major flooding concerns.

The unsettled pattern will also bring snow to the higher elevations. Several feet of snow are in the forecast for the Coast Mountains of southwestern Columbia through next weekend. Snow of this magnitude will raise the risk of avalanches.

A surge of warmer air will come onshore with the midweek storm, bringing snow levels up to over 8,000 feet in southwestern British Columbia and northwestern Washington. This warm air will trigger a rapid snowmelt, boosting runoff and raising the threat of flooding.

A northward bulge in the jet stream will bring up unseasonably warm air to the Pacific Northwest. Places such as Seattle and Portland will see record highs challenged as the mercury soars to 10 to 20 degrees above the historical average for the middle of November.

The cumulative effect of each passing storm will increase the likelihood of mudslides and other debris flows through the week and into the weekend.

More Stormy Conditions on Deck for the End of the Week

Another large storm event is predicted to roll in from the Pacific late Friday and into Saturday. This storm will also bring a brief influx of warm temperatures for the zone east of the Cascades.

The caboose of this storm train is forecast to track across a larger zone of the western U.S. over the weekend. Unlike its predecessors, this storm will bring in significantly cooler temperatures as it shifts from the coast to the southeast. Areas that dodged the earlier storms will get caught in the crosshairs of this system.

Snow levels will dip with the arrival of the cooler air. Flakes could fly at pass levels in British Columbia and the northern tier of the Cascades. It will be drenching rain that will be the story for the Pacific coast from Washington, through Oregon, and down into Northern California.

The line of moisture will expand into interior portions of Washington and Oregon, as well as the northern and central Rockies as the weekend progresses. The movement of this storm will also bring down temperatures for much of the West by next week. By Sunday, spotty rain and snow showers could hit Southern California, Nevada, and northern Arizona.

Lastly, forecasters are monitoring the possibility of a new storm coming together over the interior Southwest early next week. This would increase the chance of measurable snow for a large swath of the Rockies.

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