CW3E Event Summary: 31 January – 5 February 2025

12 February 2025

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Long-Duration Atmospheric River Produces Heavy Precipitation and Flooding in Northern California

The ARs:

  • A weak atmospheric river (AR) associated with a tropical moisture export (TME) made landfall over Washington, Oregon, and Northern California late 30 Jan.
  • A second AR associated with a much stronger TME made landfall early 1 Feb and stalled over Northern California for several days before finally dissipating early 5 Feb.
  • An AR 4 (based on the Ralph et al. 2019 AR Scale) was observed in coastal Northern California, with some locations experiencing > 100 hours of continuous AR conditions.
  • An AR 3 was also observed in northeastern California and northwestern Nevada due to inland penetration of the second AR.
  • CW3E’s AR Reconnaissance field campaign carried out eight IOPs that sampled both ARs, as well as nearby essential atmospheric structures and regions of forecast sensitivity.

Impacts:

  • At least 6–15 inches of total precipitation fell over the Northern California Coast Ranges, Klamath Mountains, southern Cascades, and Northern Sierra Nevada. A few stations recorded > 20 inches of precipitation.
  • While much of the precipitation in California fell as rain due to high freezing levels, these ARs produced an estimated 2–6 feet of snow in the highest elevations of the Klamath Mountains, southern Cascades, Northern Sierra Nevada, and Rocky Mountains in Central Idaho.
  • Heavy rainfall over multiple days caused riverine flooding in Northern California. The Pit River near Canby exceeded major flood stage.
  • The National Weather Service received numerous reports of landslides, debris flows, and flooding in Northern California.
  • Heavy snow and strong winds caused hazardous travel conditions in the higher terrain.

MIMIC-TPW2 Total Precipitable Water

Valid: 1200 UTC 29 January – 1200 UTC 5 February 2025

Click images to see loops of GFS IVT/IWV analyses

Valid 1200 UTC 29 January – 1200 UTC 5 February 2025


 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Summary provided by C. Castellano, S. Bartlett, L. DeHaan, S. Roj, M. Steen, S. Yoon, and J. Kalansky; 12 February 2025

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