CW3E Event Summary: 9-12 December 2022

December 14, 2022

Click here for a pdf of this information.

Atmospheric River with Strong Dynamical Forcing Produced Heavy Precipitation Throughout California

  • An upper-level trough over the Gulf of Alaska on 9 December deepened along the US West Coast producing a landfalling atmospheric river (AR) and heavy orographic precipitation
  • The landfalling AR was ranked as an AR2 (based on the Ralph et al. 2019 AR Scale) along the Oregon coast and an AR1 along the Central California coast
  • The deterministic GFS struggled to forecast the AR location, magnitude, and orientation at lead times > 3 days
  • The storm produced heavy precipitation along the Central California coast between the San Francisco Bay area and Santa Barbara
  • Mining Ridge received 12.80 inches of precipitation over a 72-hour period ending 9 AM 12 Dec; an R-Cat 2 according to the Ralph and Dettinger (2012) classification
  • The largest snowfall totals (> 6 feet) were observed across the higher terrain of the Sierra Nevada with the Klamath mountains receiving 1-3 feet of snowfall
  • CW3E’s surface meteorology station at Seven Oaks Dam observed 1 inch of rain during the event. Approximately 20% of water year normal precipitation has fallen at the station
  • Recent storms in California have been cold, efficient snow producers leading to a discrepancy between water year to date precipitation and current snowpack in the Sierra Nevada
  • The AR resulted in multiple rainfall-related swift water rescues, snowfall-related road closures, and dangerous backcountry avalanche conditions
  • As part of CW3E’s ongoing Atmospheric River Reconnaissance research field campaign, two flights originating from Hawaii sampled atmospheric conditions upstream of this AR in the North Pacific

Click images to see loops of NAM IVT/IWV analyses

Valid 0000 UTC 8 December – 1800 UTC 12 December 2022











Summary provided by Shawn Roj, Samuel Bartlett, Matthew Steen, Jay Cordeira, Jon Rutz, Chris Castellano, J. Kalansky, B. Kawzenuk, F.M. Ralph; 14 Dec 2022

To sign up for email alerts when CW3E post new AR updates click here.

*Outlook products are considered experimental