CW3E AR Update: 16 March 2026 Outlook

March 16, 2026

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Long-Duration Atmospheric River to Impact Washington This Week

  • An atmospheric river (AR) currently centered over British Columbia is forecast to drift southward tonight and stall over Washington and northern Oregon through Fri 20 Mar.
  • CW3E’s West-WRF ensemble is showing ≥60% likelihood of an AR 4 (based on the Ralph et al. 2019 AR Scale) over coastal Washington and ≥80% likelihood of an AR 3 over the Washington Cascade foothills.
  • There is still considerable uncertainty in the timing and magnitude of peak IVT due to forecast uncertainty in multiple possible pulses of moisture transport over the duration of the event.
  • Compared to the West-WRF initialized with GFS, the West-WRF initialized with ECMWF is forecasting a stronger final pulse of moisture transport on Fri 20 Mar, as well as longer persistence of AR conditions over the Pacific Northwest into early Sat 21 Mar.
  • The AR is forecast to produce 5–10 inches of additional precipitation over the Olympic Peninsula and North Cascades this week.
  • Marginal risk excessive rainfall outlooks (EROs) have been issued for the Olympic Peninsula and the North Cascades from Tue 17 Mar through early Fri 20 Mar due to the combination of high snow levels, melting snowpack, and multiple days of moderate rainfall.
  • Freezing levels in western Washington are forecast to remain above 7,000 feet throughout the duration of the AR, resulting in nearly all the precipitation falling as rain and facilitating rain-on-snow in areas that received heavy snowfall last week.
  • Rivers/streams in western and central Washington are forecast to rise this week due to the combination of snowmelt and rainfall. Four stream gages are currently forecast to rise above flood stage, with many others forecast to rise above action/bankfull stage.

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

Valid 0000 UTC 16 March 2026 – 0000 UTC 21 March 2026

Summary provided by C. Castellano, S. Bartlett, J. Kalansky, and M. Warner; 16 March 2026

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*Outlook products are considered experimental

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