CW3E Event Summary: 11-13 January 2021

January 14, 2021

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An Extreme Atmospheric River brought AR 5 Conditions and Widespread Hydrologic Impacts to the Pacific Northwest

• The AR initially made landfall at ~00 UTC 12 January and brought an initial pulse of IVT magnitudes >750 kg m^–1 s^–1
• A mesoscale frontal wave developed along the northern periphery of the initial AR, strengthened and moved onshore at ~00 UTC 13 January
• The secondary pulse of AR conditions was much stronger than the first (>1000 kg m^–1 s^–1) and helped to prolong the overall duration of the event, resulting in AR 5 conditions
• More than 5 inches of precipitation fell in portions of the Pacific Coast Ranges and Cascades, with the highest amounts (locally > 10 inches) in the Olympic Peninsula and extreme northwestern Oregon
• Heavy rainfall on saturated/nearly saturated soils produced widespread flooding and landslides
• High winds also caused significant tree damage and power outages in western WA and northwestern OR

Images from CIMSS/University of Wisconsin

Click images to see loops of GFS IVT/IWV analyses Valid 0000 UTC 10 January – 1200 UTC 14 January

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