CW3E AR Update: 6 October 2023 Outlook

October 6, 2023

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Pair of Atmospheric Rivers Forecast to Impact Pacific Northwest and Northern California

• A pair of atmospheric rivers (AR) are forecast to make landfall in the Pacific Northwest, the first early on Mon 9 Oct and the second on Tues 10 Oct
• AR1 conditions (based on Ralph et al. scale) are forecast during the first AR, with a ~24 hour period of IVT >500 kg m-1 s-1 forecast for Washington to Northern California
• AR2 conditions are forecast during the second AR for a more southerly latitude range along the coast of Central Oregon into Northern California, with a ~42 hour period of IVT >250 kg m-1 s-1 forecast in this region
• The 00Z GFS and 00Z ECMWF are forecasting 1 to 3 inches of precipitation over much of western Washington and Oregon over the next 10 days. Some of the precipitation is forecast to fall after the ARs
• The NWS Weather Prediction Center (WPC) is forecasting 7-day precipitation totals >3 inches over the Olympic Peninsula and 1-2 inches along the Oregon and Washington coasts and the windward (west) side of the Cascade Range
• 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

Click images to see loops of GFS IVT and IWV forecasts Valid 1800 UTC 08 October – 0600 UTC 11 October 2023

Summary provided by M. Steen, P. Iniguez and S. Bartlett; 6 October 2023

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