CW3E AR Update: 27 January 2025 Outlook

January 27, 2025

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Unsettled Weather Pattern Likely to Return to US West Coast This Week

  • Multiple tropical moisture exports (TMEs) are forecast to develop over the Northeast Pacific this week, leading to landfalling atmospheric river (AR) activity over the US West Coast.
  • The first AR is forecast to bring weak AR conditions (IVT < 500 kg m−1 s−1) to Oregon and Northern California late Thu 30 Jan into Fri 31 Dec.
  • After the initial AR landfall, a second AR is forecast to overtake the first AR and potentially stall over the US West Coast into early next week, which could result in significant precipitation amounts.
  • Ensemble and deterministic models are showing large uncertainty in the evolution of these ARs and associated precipitation after the initial AR landfall.
  • The EPS is showing a higher likelihood of landfalling AR activity continuing into early next week compared to GEFS. The EPS control run is also forecasting an AR 3 in Northern California (based on the Ralph et al. 2019 AR Scale), whereas the GEFS control is only forecasting an AR 1.
  • Compared to the deterministic GFS, the deterministic ECMWF is also forecasting stronger moisture transport over Oregon and Northern California after the initial AR landfall, as well as a more northerly track for the second AR.
  • In general, EPS is forecasting higher precipitation totals across western Oregon and Northern California during the next 10 days compared to GEFS. The deterministic ECMWF is forecasting > 10 inches of total precipitation near the Oregon/California border through the middle of next week.

Click images to see loops of GFS IVT and IWV forecasts

Valid 0000 UTC 27 January 2025 – 1200 UTC 3 February 2025

Summary provided by C. Castellano, J. Kalansky, and M. Steen; 27 January 2025

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*Outlook products are considered experimental

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