CW3E AR Update: 30 December 2025 Outlook

December 30, 2025

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Two Atmospheric Rivers to Bring Precipitation to California

  • Two atmospheric rivers (ARs) are forecast to impact over California in the next five days.
  • The first AR is forecast to make landfall along the southern California coast tonight as a subtropical moisture plume in the Northeast Pacific is driven northward by a mid-level cutoff low.
  • A deepening shortwave trough over the Northeast Pacific is forecast to facilitate cyclogenesis in the vicinity of remnant moisture from an AR that previously made landfall over British Columbia, restrengthening what is forecast to be the second AR to make landfall over California.
  • Precipitation totals are forecast to be highest over the northern Sierra Nevada. Models are forecasting multiple days of moderate-to-heavy precipitation from 1 Jan through 4 Jan for the New Bullards Bar Catchment in the Northern Sierra Nevada foothills.
  • The Weather Prediction Center (WPC) has issued slight risk (level 2 of 4) excessive rainfall outlooks (EROs) over coastal southern California and marginal risk (level 1 of 4) EROs over coastal central California on Days 2 and 3 due to heavy precipitation associated with the first AR.
  • Additionally, the WPC issued marginal risk EROs over the Sierra Nevada and coastal northern California on Days 3 through 5 and over coastal central California on Day 4 due to the precipitation associated with the second AR and surface low.
  • Precipitation is more likely to fall as rain during the first AR as the freezing levels will still be high over the Sierra Nevada. Significant snowfall is more likely during the second AR as as freezing levels continue to fall.
  • Significant riverine flooding is not currently expected as shown by the joint DWR/CNRFC forecasts. As these storms progress, it is recommended to pay close attention to the DWR/CNRFC for changes in river forecasts or to local NWS offices for flood guidance.

Click images to see loops of West-WRF IVT and IWV forecasts

Valid 0000 UTC 31 December 2025 – 0000 UTC 5 January 2026

Summary provided by M. Steen, C. Castellano, and J. Kalansky; 30 December 2025

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*Outlook products are considered experimental

For any unfamiliar terms, please refer to the American Meteorological Society Glossary.