CW3E AR Update: 28 March 2025 Outlook

March 28, 2025

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Forecast Update on Potential Atmospheric River Event Next Week

• CW3E’s previous outlook (posted on Wed 26 Mar) highlighted the strong signal for a high-impact atmospheric river (AR) in California next week in NCEP model guidance, as well as the substantial model-to-model differences between NCEP and ECMWF.
• While today’s 00Z model runs continued to show uncertainty in the forecast, the most recent 12Z NCEP guidance has shifted towards the ECMWF, which has been favoring a much weaker event for the past several days.
• Although a high-impact AR now appears unlikely, an unsettled weather pattern will bring precipitation to much of the western US through the middle of next week.
• A mid-level trough over the Northeast Pacific is forecast to produce 2–5 inches of precipitation in the Klamath Mountains, Shasta County, and Northern Sierra Nevada between Sun 30 Mar and Wed 2 Apr.
• The NWS Weather Prediction Center (WPC) has issued a marginal risk excessive rainfall outlook (ERO) for the Klamath Mountains and Northern California Coast Ranges Mon 31 Mar into early Tue 1 Apr.

Click images to see loops of GFS IVT and IWV forecasts Valid 1200 UTC 28 March 2025 – 0000 UTC 5 April 2025

Summary provided by C. Castellano; 28 March 2025

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*Outlook products are considered experimental

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