CW3E AR Update: 30 October 2023 Outlook

October 30, 2023

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Multiple Atmospheric Rivers Forecast to Impact Pacific Northwest and Northern California

  • Multiple atmospheric rivers (AR) are forecast to make landfall in the Pacific Northwest over the next 7 days, the first late Wed 1 Nov
  • AR2 conditions (based on Ralph et al. scale) are forecast during the first AR, with a ~24 hour period of IVT >800 kg m-1 s-1 forecast for Washington to Northern California in both the GFS and ECMWF
  • There is disagreement in the timing, strength and duration of the ARs that follow between the models
  • The GFS is forecasting AR1 conditions during the second AR along the coast of Central Oregon into Northern California early Sat 4 Nov, with a ~15 hour period of IVT >700 kg m-1 s-1 forecast in this region
  • The second AR is forecast to make landfall late Fri 3 Nov in the ECMWF, where EPS ensemble members are forecasting the second AR to be stronger and for AR conditions to persist longer than the GEFS, resulting in significant differences in precipitation forecasts
  • GEFS ensemble members show uncertainty of the forecast conditions for the third AR to register on the Ralph et al. scale, while the EPS shows many members forecasting AR conditions persisting from the second AR through to the third with the arrival of the next moisture corridor
  • The NWS Weather Prediction Center (WPC) is forecasting precipitation totals >1.5 inches during the first AR for the Olympic Peninsula, Cascade Range and Washington and Oregon Coasts
  • Precipitation associated with these ARs are forecast to be primarily beneficial to the Pacific Northwest where widespread drought conditions are present, with no river levels forecast to rise above action stage within the boundaries of the NWS Northwest River Forecast center
  • Most of the precipitation is expected to fall as rain, with freezing levels forecast to stay above 6000 feet throughout these events

Click images to see loops of GFS IVT and IWV forecasts

Valid 1800 UTC 01 November – 0600 UTC 06 November 2023











Summary provided by M. Steen, P. Iniguez, S. Bartlett, C. Castellano, S. Roj and J. Kalansky; 30 October 2023

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