CW3E AR Update: 18 September 2020 Outlook

September 18, 2020

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A Potentially Strong Atmospheric River Could Douse the Pacific Northwest Next Week

  • Model forecasts are currently indicating the potential for a strong AR to make landfall over the PNW next week, but large ensemble spread in IVT forecasts is leading to considerable uncertainty in AR Scale (ranging from no AR to AR 5 in some locations)
  • Forecasts of maximum IVT magnitude over the Washington Coast range from < 400 kg m–1 s–1 to > 1200 kg m–1 s–1
  • While forecast uncertainty is currently high, more than 4 inches of precipitation are possible over the Olympic Peninsula during the next 7 days (Note: the 7-day forecast may not encompass the entirety of this event)

Click images to see loops of GFS IVT/IWV analyses and forecasts

Valid 1200 UTC 18 September – 1200 UTC 28 September 2020








Summary provided by C. Hecht, C. Castellano, B. Kawzenuk, J. Kalansky, and F. M. Ralph; 18 September 2020

*Outlook products are considered experimental