CW3E AR Update: 13 March 2026 Outlook

March 13, 2026

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Potential Long-Duration Atmospheric River to Bring Heavy Precipitation to Washington

  • Ensemble guidance is showing high confidence in a prolonged period of atmospheric river (AR) conditions over the Pacific Northwest beginning this weekend and continuing through next week.
  • Following the AR currently bringing precipitation to the PNW, an AR fueled by ample low-latitude moisture strengthening over Hawai’i is forecast to propagate northeast toward British Columbia and the Pacific Northwest over the next couple days.
  • The core of the next AR is forecast to make landfall primarily over the British Columbia coast, with weak AR conditions initially forecast over the Pacific Northwest.
  • A shortwave trough is forecast to drive the core of the next AR south over the Pacific Northwest. There is potential for a second pulse of strong IVT extending the AR conditions between Wed 18 and Thu 19 Mar.
  • The forecast confidence in the southerly shift of the AR has increased in the last 36-hours./li>
  • There is still large uncertainty in the forecast onset of AR conditions, timing and magnitude of maximum IVT, and duration of AR conditions.
  • There is also large uncertainty in the precipitation forecasts over coastal and higher elevations of Washington between Sun 15 Mar and Fri 20 Mar.
  • Freezing levels are forecast to rise substantially at the onset of this event across the Pacific Northwest. The GEFS ensemble mean indicates that freezing levels are forecast to rise from ~2,000 feet at 11 PM PT Sun 15 Mar to > 8,000 feet by 11 PM PT Mon 16 Mar over the Olympic Peninsula and the Washington Cascades.
  • The much higher forecast freezing levels suggest that most of the precipitation across Washington/Pacific Northwest is forecast to fall as rain, potentially leading to snowmelt and rain-on-snow following the recent heavy snowfall.
  • While hydrologic impacts are expected in Washington, the locations and magnitudes are currently unknown due to uncertainty in the forecast of the next AR and the extent of lowland snow from the current AR impacting the Pacific Northwest.
  • Continue to monitor local NWS Weather Forecast Offices and the Northwest River Forecast Center for the most up to date forecast information.

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

Valid 0000 UTC 14 March 2026 – 0600 UTC 21 March 2026

Summary provided by M. Steen, C. Castellano, S. Bartlett and M. Warner; 13 March 2026

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