An unsettled weather pattern is set to dominate the U.S. West Coast through early next week, with multiple atmospheric rivers (ARs) poised to deliver heavy precipitation, raising concerns about flooding, landslides, and widespread disruptions. This follows a potent AR event on March 23 that already triggered flooding and a landslide in British Columbia.
A second, more intense AR is forecast to slam into the West Coast on Wednesday, March 26, targeting coastal Oregon with moderate AR conditions (Integrated Vapor Transport, IVT, ≥500 kg/m/s). Fueled by a strong low-pressure system stalling offshore, this storm's cyclonic flow could extend AR conditions (IVT ≥250 kg/m/s) through March 28.
Expect heavy rain, with western Washington, western Oregon, and far Northern California in the crosshairs for 50–125 mm (2–5 inches) of precipitation. The Olympic Mountains and Oregon-California border could see even higher totals.
Uncertainty looms as a third AR is projected to strike California on Sunday, March 30. The Global Forecast System (GFS) predicts a powerful southwesterly IVT hitting Central California, while the European Centre (ECMWF) leans toward a weaker, westerly flow over Southern California. The Center for Western Weather and Water Extremes (CW3E) AR Landfall Tool suggests a 60–80% probability of AR conditions persisting into April 1–2, with coastal Washington, Oregon, and Northern California facing a >90% chance of significant impacts on March 26.
Ongoing AR (March 25): The Olympic Peninsula and Washington Cascades could see an additional 25–50 mm (1–2 inches) of rain, with a marginal excessive rainfall risk (≥5%; level 1 of 4) through 05:00 PST.
Second AR (March 26–28): Western Washington, Oregon, and far Northern California are braced for 50–125 mm (2–5 inches), with potential for more in elevated areas.
Snowfall: Warm temperatures will limit snow accumulation, with freezing levels in the Washington Cascades spiking to 3,050 m (10,000 feet) before plunging to 1,830 m (6,000 feet) post-AR.
Northern and Central California face a wild card in the coming days. Ensemble forecasts from GEFS and ECMWF predict over 100 mm (4 inches) of mean areal precipitation in the Upper Yuba watershed, but the range is staggering—some models suggest as little as 50 mm (2 inches), while others warn of totals exceeding 175 mm (7 inches). This uncertainty, driven by shifting AR trajectories, could spell trouble for flood-prone regions.
The relentless parade of atmospheric rivers threatens to overwhelm the West Coast with heavy rain, potential flooding, and landslides. Residents should prepare for travel disruptions and monitor local warnings as these powerful systems unfold. Stay tuned for updates as forecast confidence sharpens closer to the weekend. Forecast data sourced from NOAA, CW3E, GFS, and ECMWF models.
