CW3E AR Update: 26 March 2025 Outlook

March 26, 2025

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Pair of Atmospheric Rivers Forecast to Impact the US West Coast

AR Summary:

  • An atmospheric river (AR) that made landfall today will continue to impact the Pacific Northwest into early Fri 28 Mar.
  • There is potential for an impactful AR to landfall over California next week, but model-to-model uncertainty is high.
  • The GFS is forecasting a strong AR to make landfall along the CA coast and penetrate inland to the Sierra Nevada with optimal landfall direction for orographic precipitation enhancement.
  • The dynamics over the NE Pacific are much different in the ECMWF, resulting in the AR briefly making landfall along the USWC with suboptimal landfall direction, limiting the precipitation impact.

Precipitation Forecasts:

  • The NWS Weather Prediction Center (WPC) is forecasting at least 4-7 inches inches of precipitation over the Olympic Peninsula, Oregon, and the Northern California Coast Ranges with the first AR./li>
  • The GFS forecast for precipitation with the second AR is greater than the ECMWF due to the forecast differences in the AR.
  • The GFS is forecasting 7+ inches across the California Coast Ranges and Sierra Nevada, with highest totals of 10+ inches over the Sierra Nevada while the ECMWF is forecasting 2-4 inches over the Northern Sierra Nevada and Oregon and Northern California Coast Ranges.

Flooding and Streamflow:

  • The NWS WPC has issued a marginal risk Excessive Rainfall Outlook (ERO) (level 1 of 4, 5% chance of flash flood conditions) over the Cascades in Washington and Oregon on Day 1 (24-h period ending 5 AM PT Thu 27 Mar) and over coastal Washington, Oregon, and Northern California on Day 2 (24-h period ending 5 AM PT Fri 28 Mar).
  • The NWS Northwest River Forecast Center is forecasting three gauges in Oregon to exceed minor flood stage and one gauge in Oregon to exceed moderate flood stage over the next 10 days.

Click images to see loops of GFS IVT and IWV forecasts

Valid 1200 UTC 26 March 2025 – 1500 UTC 28 March 2025

Summary provided by M. Steen, C. Castellano, and S. Bartlett; 26 March 2025

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*Outlook products are considered experimental

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