CW3E AR Update: 3 December 2021 Outlook

December 3, 2021

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Multiple atmospheric rivers are forecast to make landfall over the US West Coast

  • Two ARs and their parent lows are forecast to bring rain to the Pacific Northwest and parts of California over the next week
  • These ARs are primarily being steered by persistent high pressure in the Eastern Pacific, which is resulting in a northwesterly orientation as the ARs make it to California
  • Due to the northwesterly orientation of the IVT, the precipitation from these ARs will likely be much less than an AR of similar magnitude but a southwesterly orientation
  • The parent lows of these ARs are forecast to move inland over the Pacific Northwest, which may result in very low freezing levels and snow showers at low elevations
  • The WPC is currently forecasting ~3–5 inches of precipitation over the Cascades in Washington and 0.5 – 1.5 inches over the Sierra Nevada and Southern California Mountains

Click images to see loops of GFS IVT & IWV forecasts

Valid 1200 UTC 3 December – 0000 UTC 13 December 2021









Summary provided by C. Hecht, S. Roj, J. Cordeira, C. Castellano, B. Kawzenuk, J. Kalansky, and F. M. Ralph; 3 December 2021

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