Storm siege to raise flooding, avalanche risks across Pacific Northwest
One of the most significant rounds of storms of the winter will impact the Northwest into the start of next week. The most potent storm this weekend will pack an atmospheric river.
You never want to be near an avalanche when they happen, but if you are, here are expert safety tips from an avalanche forecaster.
In one of the more active weather patterns of the winter, a series of storms will roll across the northern Pacific Ocean and into the northwestern United States and southern British Columbia, Canada, into early next week. The cumulative nature of the storms can pack a punch in terms of rain and high country snow, AccuWeather meteorologists say.
One of the storms this weekend will have behavior and impacts to that of an atmospheric river.
Rounds of precipitation will roll ashore every one to two days with the amount of low- and intermediate-elevation rain and high-country snow varying in intensity. The first storm moved through the area Wednesday and Wednesday evening and brought a soaking rainfall.
Warmer air will invade ahead of the weekend storm, which could bring the most precipitation.
"There will be a traceable long plume of moisture that will likely extend to north of Hawaii and all the way back to the western Pacific," AccuWeather Senior Meteorologist Heather Zehr said, "The weather community refers to these as atmospheric rivers."
The Center For Western Weather and Water Extremes at Scripps Institution of Oceanography forecasts a strong to extreme atmospheric river with this system a 4 or 5 on their scale ranging from 1 to 5.
The weekend storm will also pack the most wind of the storms in the series, with gales along the Washington and Oregon coasts. As is often the case with potent winter storms rolling ashore in the Northwest, there will be the risk of sporadic downed tree limbs and power outages.
"Snow levels will soar up to nearly 8,000 feet on Saturday in the Cascades, and with a heavy rain of precipitation that gets into western Oregon and Washington, it may trigger some trouble," Zehr said. "The combination of melting snow over the higher elevations, rain and rising temperatures will lead to significant runoff."
Small streams and the short-run rivers flowing out of the mountains will swell and can lead to quick flooding. In steep terrain, there will be some risk of rock slides and other debris flows along secondary roads.
During the storm siege, 2-4 inches of rain is likely to fall in the lower elevations along Interstate 5 in Washington and Oregon, with slow travel at times. However, much heavier rain will fall on the western slopes of the Coast Ranges and the lower to intermediate, west-facing slopes of the Cascades. From 4 to 8 inches of rain may pour down into early next week with an AccuWeather Local StormMax™ of 14 inches.
"The rising freezing levels with rain falling on top of the recent snow over the high country are a recipe for avalanches," Zehr said.
Over the highest ridges and peaks of the Olympics and Cascades, a whopping 5-10 feet of snow may pile up in the pattern.
A view of four of the central Oregon Cascade Mountain Range peaks, from left, Broken Top, South Sister, Middle Sister and North Sister, as seen from near Sisters, Oregon, on April 24, 2018. (AP Photo/Don Ryan, File)
Rainfall in Seattle since the start of the year is only about one-third of typical amounts, with just over 3 inches falling compared to the historical average of 8.30 inches as of Tuesday, Feb. 18. Similarly, rainfall in Vancouver, British Columbia, has been just shy of 40% of average.
There has been a bit more rain farther south toward Portland and Eugene, Oregon, with 60 and 70% of the historical average since Jan. 1.
East of the Cascades, precipitation has been much closer to the historical average since 2025 began with nearly 90% in Spokane, Washington, and a bit better than 100% in Pendleton, Oregon.
Even farther to the east, in western Montana and much of Idaho, precipitation has been average to much greater than average for the year so far. The melted amount of snow combined with rain has been 160% of average in Boise, Idaho, and 260% of historical levels in Great Falls, Montana.
Precipitation from most of the storms into early next week will steer clear of Central and Southern California.
While some low intensity wind events are forecast for coastal areas of Southern California into next week, rain from recent storms should have the landscape and vegetation moist enough to keep the risk of wildfire ignition low, Zehr said.
Want next-level safety, ad-free? Unlock advanced, hyperlocal severe weather alerts when you subscribe to Premium+ on the AccuWeather app. AccuWeather Alerts™ are prompted by our expert meteorologists who monitor and analyze dangerous weather risks 24/7 to keep you and your family safer.
Report a Typo
