CW3E AR Update: 17 February 2023 Outlook

February 17, 2023

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Atmospheric River Forecast to Bring Precipitation to the Pacific Northwest and Northern California

  • An atmospheric river (AR) is forecast to make landfall in the Pacific Northwest on Sunday and bring precipitation to Washington, Oregon, and Northern California through mid-day on Wednesday
  • IVT > 600 kg m-1 s-1 is forecast during landfall along the coast of Washington, bringing AR 2 conditions (based on the Ralph et al. 2019 AR Scale) to coastal locations of the Pacific Northwest
  • This AR is forecast propagate over the ridge positioned in the eastern North Pacific, bringing primarily northwesterly/westerly IVT to the US West Coast, eventually dissipating along the coast of California by late Wednesday
  • A weak mesoscale frontal wave is forecast to occur during the mid-stage of this AR over the Gulf of Alaska, which will have weak secondary cyclogenesis in association with a mid-level shortwave trough
  • The 00Z GFS is forecasting a stronger and longer duration period of AR conditions for points along the coast as compared to the ECWMF, with the GFS bringing AR conditions south to coastal locations in Northern California
  • The 00Z GFS is forecasting greater 7-day watershed precipitation totals throughout northern California, Oregon, and Washington than the 00Z ECMWF, especially within coastal watersheds along the CA/OR border and the Oregon Cascades
  • The 12Z GEFS ensemble is forecasting snow levels to fall dramatically from > 3,000 m to near sea level by 12Z 22 Feb for much of Northern California and the Sierra Nevada Mountains, resulting in the potential for snowfall accumulation at lower elevations than usual elevations

Click images to see loops of GFS IVT and IWV forecasts

Valid 1200 UTC 18 February – 1800 UTC 22 February 2023







Summary provided by S. Bartlett, S. Roj, C. Castellano, and F. M. Ralph; 17 February 2023

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