CW3E AR Update: 14 October 2021 Outlook

October 14, 2021

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Prolonged Period of Active Weather Expected in the Pacific Northwest

• An atmospheric river (AR) will make landfall across Washington early Friday morning
• AR 3 conditions (based on the Ralph et al. 2019 AR Scale) are forecasted in coastal Washington
• Limited moisture and weak storm dynamics are expected to constrain precipitation totals outside of the Olympic Peninsula and North Cascades
• After a brief lull, a period of very active weather is forecasted to impact to the U.S. West Coast, with a series of landfalling ARs becoming increasingly likely during 20–24 October
• The highest forecast confidence in landfalling AR activity during this period is in Northern California, Oregon, and Washington, but there is considerable uncertainty in the evolution of these ARs and their associated low-pressure systems

Click images to see loops of GFS IVT & IWV forecasts Valid 1200 UTC 14 October – 0000 UTC 18 October 2021

Summary provided by C. Castellano, C. Hecht, B. Kawzenuk, J. Kalansky, and F. M. Ralph; 14 October 2021

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