Pineapple Express to soak western US with rain, snow

Days of rain are forecast to hit portions of the Northwest and California, bringing the risk of flooding and landslides. While the rain may subside a little more quickly in some locations, snow is expected to take its place and bring a new set of challenges, AccuWeather meteorologists warn.
"A major weather event, known as an atmospheric river, is forecast to unfold Friday and continue into the middle of next week, sending waves of moisture to the West Coast," said AccuWeather Senior Meteorologist Adam Douty.
An atmospheric river is a phenomenon that occurs when moisture consolidates and travels a long distance only to be deposited someplace else. This can happen anywhere in the globe but is often noticed along the West Coast of the United States. The funneling of tropical moisture, specifically from the central Pacific, near Hawaii, into the U.S. is known as the Pineapple Express.
Over the next week, the Pineapple Express is expected to unload on the Pacific Northwest and the northern half of California, bringing the risk of flooding rain and snow.
The winter months are typically the wettest time of the year for California and the Northwest, so the region is no stranger to rain and snow in late January and February. However, it's been abnormally dry since the start of 2025.
San Francisco has reported only 0.13 of an inch of rain since Jan. 1, when the historical average for the month is around 3.9 inches. Redding, California, has reported 0.63 of an inch, a minuscule 10% of the norm for January. The recent dry conditions could further the risk of flooding as heavy rain moves into the region.
Through Monday, the atmospheric river is expected to point right to the Northern California coast, bringing with it the biggest rainstorm so far this year.
With so much rain in just a few days, there will be a heightened risk of flooding. In the more mountainous terrain, landslides will also be a concern. Both flooding and landslides could lead to travel delays or even road closures. Air travel is also expected to be impacted given the multiday event of gusty winds and rain.
Widespread rainfall amounts of 1-2 inches are expected for San Francisco and the Bay Area northward to northwestern Oregon, with over half a foot of rain in portions of Northern California. An AccuWeather Local StormMax™ of 24 inches is most likely in this area.
In addition to heavy rain falling in the valleys, higher terrain is also expected to be impacted.
"Unlike with many other winter storms in the past two years, temperatures will be too high for significant snowfall in the Sierra Nevada," Douty said.
Snow levels in the Sierra will be lowest, around 7,000 feet, as the storm moves in Friday afternoon and evening, Douty noted, adding that snow levels will rise to almost 9,000 feet and stay there through the weekend. Snow at this high altitude is well above pass level.
The mountains, currently covered in feet of snow, can expect several inches of rain, further raising concerns of flooding.Have the app? Unlock AccuWeather Alerts™ with Premium+
Another wave of moisture is expected early next week and may bring a push of colder air and the risk of snow in the higher terrain of Northern California.
"Snow levels are then expected to fall early next week which will bring potential travel impacts across the passes," Douty warned.
The Pacific Northwest will also be impacted by the atmospheric river, with waves of rain and snow forecast to hit the area.
The bulk of the precipitation is forecast through Friday night. The highest rain amounts, on the order of 1-2 inches, is expected across coastal Washington and Oregon.
In contrast to locations farther south in California, the mountains of the Cascades and northern Rockies in Idaho can expect rounds of snow.
Snow levels will be lowering into Friday night with slow and slippery travel through Snoqualmie Pass on Interstate 90.
By the start of the weekend, most of the moisture from the atmospheric river will be pushed into Northern California. While heavy rainfall is expected to end in most of Washington and Oregon by that time, showery and wintry conditions are expected to continue.
This weekend, there will most likely be a dry zone to the immediate east of the Cascades. Still, some rain and wet snow can fall in eastern parts of Washington and Oregon on Saturday night and Sunday.
"Enough cold air is expected to infiltrate the Northwest in time for the weekend for continued snow showers in the mountains. However, flakes may also reach the lowland areas," Douty said.
Snowflakes are possible in the major cities of Portland and Seattle as temperatures fall on Saturday night. There is even the potential for Seattle to get some accumulating snow.
Seattle has yet to have any accumulating snow this winter, but its last experienced measurable snow occurred on March 3, 2024, when 0.3 of an inch fell.
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.

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