CW3E AR Update: 11 October 2023 Outlook

October 11, 2023

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Several ARs to Move Across the Pacific Northwest During the Next Week

  • Several Atmospheric Rivers (ARs) will impinge on the Washington, Oregon, and Northern California coasts beginning Friday (Oct 13) and continuing into early next week
  • Weak AR1-2 conditions (based on the Ralph et al. 2019 AR Scale) are likely Friday afternoon through Sunday (Oct 15) along the WA/OR coastal areas with the 1st and 2nd ARs
  • The jet stream will remain very active across the North Pacific Ocean early next week, providing optimal conditions for continued AR activity in the Monday (Oct 16) to Wednesday (Oct 18) timeframe
  • However, there is considerable model uncertainty surrounding the details of the 3rd AR
  • In total, AR1 or stronger conditions are likely (90%) from Point Reyes, CA and northward around Monday. There is a moderate chance (70%) of up to AR3 conditions along the WA and OR coasts during this time and a low (20%) chance for AR5 conditions along the OR coast
  • Through the next seven days, 2-5” of rain are expected along the coastal mountains and Cascades with localized higher amounts possible
  • Snow levels will remain elevated and mostly above 8,000’ through the event
  • While notable rain is forecast and area rivers will rise, currently no rivers are forecast to exceed flood stage
  • With much more uncertainty, there is potential for a 4th AR later next week

Click images to see loops of GFS IVT and IWV forecasts

Valid 0000 UTC 11 October – 1200 UTC 17 October 2023









Summary provided by P. Iniguez, C. Castellano, M. Steen, and S. Bartlett; 11 October 2023

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