CW3E AR Update: 9 March 2026 Outlook

March 9, 2026

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Atmospheric Rivers Forecast to Bring Heavy Rain and Snow to the Pacific Northwest

  • An atmospheric river (AR) featuring multiple pulses of moisture transport is forecast to make landfall over the Pacific Northwest late Tue 10 Mar and continue to impact the region into early Sat 14 Mar.
  • After the initial AR begins to weaken, a second and potentially stronger AR associated with a northward surge of tropical and subtropical moisture is forecast to make landfall between British Columbia and Oregon early Sun 15 Mar, but there is considerable uncertainty in the landfall location and evolution of this AR.
  • CW3E’s West-WRF ensemble is showing a ≥75% probability of an AR 3 or greater (based on the Ralph et al. 2019 AR Scale) over southwestern Washington and northwestern Oregon in association with the first AR period.
  • There is still considerable uncertainty in the timing and magnitude of the individual IVT pulses during the first AR period, as well as the start/end time of AR conditions.
  • Marginal risk excessive rainfall outlooks (EROs) have been issued in portions of southwestern Washington and northwestern Oregon for Wed 11 Mar through early Sat 14 Mar due to heavy rainfall during the first AR period.
  • The NWS Weather Prediction Center is forecasting 7–15 inches of total precipitation in the Olympic Mountains, northern Oregon Coast Ranges, Washington Cascades, and northern Oregon Cascades over the next 7 days.
  • Freezing levels in western Washington are forecast to fluctuate during the first AR period, but will likely be low enough to facilitate significant snowfall accumulations above 3,000 feet in the Olympic Mountains and Cascades.
  • Total snowfall accumulations are forecast to exceed 48 inches in the higher terrain of the Olympic Mountains and Washington Cascades by early Sat 14 Mar.
  • Heavy precipitation from these ARs is forecast to result in river/stream level rises in western Washington and northwestern Oregon over the next 10 days. Four stream gages are currently forecast to rise above flood stage.
  • CW3E’s AR Recon field campaign is planning a sequence of flights to sample these ARs, nearby essential atmospheric structures, and regions of high forecast sensitivity with the goal of improving precipitation forecasts.

Click images to see loops of West-WRF IVT and IWV forecasts

Valid 0000 UTC 9 March 2026 – 1200 UTC 16 March 2026

Summary provided by C. Castellano, S. Bartlett, M. Steen, and A. Wilson; 9 March 2026

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*Outlook products are considered experimental

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