Two atmospheric rivers forecast to make landfall over the Pacific Northwest and northern California

Two atmospheric rivers (ARs) are forecast to hit the Pacific Northwest and northern California from late Thursday, October 23, through Monday, October 27.

The first and stronger AR is expected to make landfall over Washington late Thursday, move south along the coast, and dissipate over northern California by Sunday, October 26.

AR3 conditions with integrated vapor transport (IVT) values of over 800 kg m^-1s^-1 are forecast over western Washington, with some models forecasting AR4 intensity.

According to the Center for Western Weather and Water Extremes (CW3E) forecast models, show a probability of 80 to 100% of AR conditions (IVT > 250 kg m^-1s^-1) along the Washington, Oregon, and northern California coastlines due to the first AR’s impact

A mesoscale frontal wave (MFW) is forecast to develop within this first AR, producing a secondary low-pressure center offshore and a dual peak in IVT for coastal Oregon and Washington. This could locally intensify rainfall rates, prolonging AR conditions through late Saturday, October 25.

A second, weaker, and more zonally oriented AR is forecast to make landfall on, bringing additional moisture to southern Oregon and northern California. Forecast remains uncertain for this AR; the ECMWF model shows a stronger low-pressure area and higher IVT, while the GFS forecasts a weaker feature and shorter duration.

The Weather Prediction Center (WPC) has forecast 50–100 mm (2–4 inches) of rainfall across coastal Washington, Oregon, and northern California through Sunday.

Locally higher totals of 130 mm (5 inches) over the Olympic Peninsula, the Cascades, and the coastal ranges of Oregon and northern California. A Marginal Risk for Excessive Rainfall has been issued for these regions from Friday through Sunday due to the risk of flash floods.

Freezing levels are expected to begin near 2 400 m (8 000 feet), resulting in rainfall over most elevated terrain early in the event, before dropping below 1 200 m (4 000 feet) on Sunday. Falling freezing levels imply high-elevation snow accumulation and increase the risk of rain-on-snow runoff where snowpack exists.

NWS Portland has issued gale watches along the Oregon Coast and warned of high surf and sneaker-wave risk. NWS Medford reports hazardous beach conditions, strong coastal winds, and potential snowfall exceeding 400 mm (16 inches) over the Cascades.

Ensemble precipitation forecasts for representative watersheds show totals near 50 mm (2 inches) over the Snoqualmie Basin and 70–120 mm (3–5 inches) over the Lower Klamath Basin, consistent with the spread among GEFS and EPS members.

CW3E’s landfall tool indicates a 70–85 percent probability of renewed AR activity after October 27, beginning October 31 or November 1 along the Pacific Northwest and northern California coasts.

References:

¹ AR Update – CW3e – October 22, 2025

Rishav Kothari

I am an Assistant Editor and Severe Weather & Science Journalist at The Watchers, specializing in real-time severe weather coverage, geophysical event reporting, and research-driven scientific analysis. You can reach me at rishav(at)watchers(.)news.

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