CW3E Event Summary: 28 February – 3 March 2024

8 March 2024

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Atmospheric River and Winter Storm Produce Heavy Snow Across Western US

  • An atmospheric river (AR) and a slow-moving mid-level trough fueled a long-duration precipitation event over the Western US during 28 Feb – 3 Mar.

The AR:

  • The AR made landfall over the Pacific Northwest late on 27 Feb, producing AR2 conditions (based on the Ralph et al. 2019 AR Scale) along the coast of southern Washington, Oregon, and far Northern California.
  • After the initial landfalling AR weakened, a second pulse of moisture transport brought another period of AR conditions to Northern and Central California.
  • The initial AR landfall and the second pulse of moisture transport combined to produce AR1–2 conditions in the foothills of the Sierra Nevada and played a key role in supporting very heavy snowfall accumulations.


  • The heaviest precipitation (> 6 inches liquid equivalent) was observed in the Pacific Coast Ranges and Sierra Nevada.
  • An estimated 4–10 feet of snow fell in the Northern and Central Sierra Nevada, with the highest totals near Lake Tahoe.
  • About 2–4 feet of snow fell in the Olympic Mountains, Cascades, Klamath Mountains, and Southern Sierra Nevada.
  • Low freezing levels also facilitated significant snowfall accumulations (> 12 inches) in the Willapa Hills, Oregon Coast Ranges, and Northern California Coast Ranges.
  • This event provided a substantial boost to seasonal snowpack in the Sierra Nevada, with many stations reporting snow water equivalent (SWE) increases of 8–12 inches (~20–30% of the typical peak SWE) over a 5-day period.
  • Heavy snowfall and high winds created extremely dangerous travel conditions, resulting in closures of I-80 and US-395.

Click images to see loops of GFS 500-hPa Geopotential Height/Vorticity and IVT analyses

Valid: 1200 UTC 27 February – 1200 UTC 4 March 2024

Valid: 0000 UTC 28 February – 0000 UTC 2 March 2024


















Summary provided by C. Castellano, S. Bartlett, P. Iniguez, J. Kalansky, and G. Lewis; 8 Mar 2024

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