CW3E AR Update: 20 December 2023 Outlook

December 20, 2023

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Atmospheric River Forecast for US West Coast Landfall on Christmas

  • An Atmospheric River (AR) is forecast to make landfall in the Pacific Northwest (PNW) early Mon 25 Dec and continue through Wed 27 Dec.
  • The GEFS control run is forecasting AR3 to AR4 conditions (based on Ralph et al. 2019 AR scale) for the PNW.
  • Due to the long lead time with this event, there is uncertainty in the AR landfall timing and duration in the GEFS, ECMWF EPS and West-WRF Ensemble.
  • The NWS Weather Prediction Center (WPC) is currently forecasting 3-day precipitation totals ≥ 2” with highest precipitation totals over the Olympic Peninsula and CA/OR border.
  • The NWS Climate Prediction Center’s Day 8-14 Hazard Outlook shows risks of heavy precipitation, heavy snow and high winds for Northern CA from 12/27 through 12/30.

Click images to see loops of GFS IVT and IWV forecasts

Valid 0600 UTC 24 December 2023 – 0000 UTC 28 December 2023












Summary provided by M. Steen, S. Bartlett, and S. Roj; 20 December 2023

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