CW3E AR Update: 19 December 2025 Outlook

December 19, 2025

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Active Period with Multiple Atmospheric Rivers Forecast over California this Weekend into Next Week

An atmospheric river (AR) currently located over the US West Coast is forecast to shift southward into Northern and Central California through early Sat 20 Dec. This AR will be followed by a second AR that is forecast to develop late Sat 20 Dec and bring AR conditions to Northern and Central California through Mon 22 Dec.
A third, stronger AR is forecast to develop in association with a mid-level trough on Tue 23 Dec and bring strong southwesterly IVT >750 m^-1 s^-1 over Central and Southern California through Thu 25 Dec.
CW3E’s West-WRF ensemble control member is forecasting AR3 conditions along coastal Northern California with the first and second ARs and AR3 conditions along coastal Central and Southern California with the third AR.
CW3E’s ECMWF AR Landfall tool is showing high confidence (90–100% probability of IVT >250 m^-1 s^-1) over coastal Northern and Central California with the first and second ARs during Sat 20 Dec–Mon 22 Dec, followed by a period of high confidence (75–95% probability) in AR conditions over Central and Southern California during Tue 23 Dec–Thu 25 Dec.
The NWS Weather Prediction Center (WPC) is forecasting 7-day rainfall amounts of 10–20 in. over the Sierra Nevada, 7–10 in. over the Coast Ranges of Northern and Central California, and 3–7 in. over the Transverse Ranges in Southern California.
WPC has also issued marginal risk (level 1 of 4; ≥5% probability of flash flooding) excessive rainfall outlooks (EROs) over Northern California for Fri 19 Dec–Wed 24 Dec and slight risk (level 2 of 4; ≥15% prob.) EROs for Sun 21 Dec–Wed 24 Dec.
Despite these high precipitation totals, significant riverine flooding is not currently forecast in California as shown by the joint DWR/CNRFC forecasts. As these storms progress and soil conditions become more saturated, it is recommended to pay close attention to the DWR/CNRFC forecasts for changes in river forecasts or to the local NWS offices for local flood guidance.
Freezing levels over the Sierra Nevada with the first and second AR are forecast to start above ~9,000 feet and gradually lower to ~7,000 ft during the third AR. This will limit significant snowfall with the first and second AR, and facilitate significant snowfall accumulations during the third AR, particularly in the Central and Southern Sierra Nevada.