CW3E Event Summary: 19-26 February 2023

3 March 2023

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Active Weather Pattern Brings Heavy Rain and Low-Elevation Snow to Western US

  • An atmospheric river (AR) made landfall over the Pacific Northwest on 19 February
  • AR 1/AR 2 conditions (based on the Ralph et al. 2019 AR Scale) were observed across much of coastal Washington
  • The storm produced more than 6 inches of storm-total precipitation in Western Washington and up to 2 feet of snow in the Washington Cascades
  • As the AR propagated south along the US West Coast and dissipated, an upper-level shortwave trough and associated area of low pressure formed over British Columbia
  • As this trough deepened along the US West Coast, unsettled weather with low-elevation snow continued
  • A second AR formed in association with the trough and made landfall over Central California on 24 February
  • This storm featured strong upper-level dynamics and a favorable moisture flux direction for heavy orographic precipitation along the Transverse Ranges of Southern California
  • The heaviest storm-total precipitation, >10 inches, fell in the western Transverse Range with accumulations >6 inches elsewhere in the Transverse Ranges and the southern Sierra Nevada.
  • More than 36 inches of snow fell throughout the Transverse Ranges with >72 inches in parts of the southern Sierra Nevada
  • Very low freezing levels and ample moisture allowed for snow in locations that rarely see snow accumulations
  • The combination of heavy rainfall and high antecedent soil moisture and streamflow conditions led to riverine and urban flooding

Click images to see loops of NAM IVT/IWV analyses

Valid 0000 UTC 18 February – 1800 UTC 27 February 2023






















Summary provided by Shawn Roj, Samuel Bartlett, Chris Castellano, J. Kalansky, F.M. Ralph; 3 Mar 2023

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