CW3E AR Update: 10 March 2025 Outlook

March 10, 2025

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Multiple Atmospheric Rivers Forecast to Impact US West Coast This Week into This Weekend

  • A weak atmospheric river (AR) is forecast to make landfall over coastal Oregon late Tue 11 Mar.
  • As the upstream trough amplifies off the California coast, the AR is forecast to intensify over California, potentially bringing moderate AR conditions (IVT ≥ 500 kg m−1 s−1) to the Bay Area and Sacramento Valley.
  • A second and potentially stronger AR is forecast to make landfall over the US West Coast this weekend in association with a strong low-pressure system.
  • The GEFS control member is forecasting an AR 1 (based on the Ralph et al. 2019 AR Scale) over the Bay Area in association with the first AR.
  • While moisture will be somewhat limited with these ARs, strong dynamical forcing and a favorable direction of moisture transport will likely facilitate heavy precipitation over the US West Coast.
  • The first AR is forecast to produce 2–5 inches of precipitation in the Northern California Coast Ranges, Sierra Nevada, and eastern Transverse Ranges, and 1–3 inches of precipitation elsewhere in coastal California.
  • The NWS Weather Prediction Center (WPC) has issued a slight risk excessive rainfall outlook (ERO) for the Transverse Ranges and a marginal risk ERO for the rest of coastal California, the Sacramento Valley, and the Sierra Nevada foothills.
  • Low freezing levels during the first AR will facilitate heavy snowfall accumulations (at least 12–36 inches) above 4,000 feet throughout the Sierra Nevada. Major-to-extreme winter storm impacts are expected in these areas.
  • Model differences in the evolution of the second AR and associated upstream trough are leading to large differences in forecast precipitation over California during the next 10 days. The EPS is favoring much higher precipitation totals over coastal California and the Sierra Nevada compared to GEFS.

Click images to see loops of GFS IVT and IWV forecasts

Valid 1200 UTC 10 March 2025 – 0000 UTC 18 March 2025

Summary provided by C. Castellano and M. Steen; 10 March 2025

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*Outlook products are considered experimental

For any unfamiliar terms, please refer to the American Meteorological Society Glossary.