CW3E AR Update: 12 November 2025 Outlook

November 12, 2025

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Atmospheric River Forecast to Bring Heavy Precipitation to California Later this Week

  • A strong atmospheric river (AR) that developed offshore today in association with a deep trough and area of enhanced subtropical moisture is forecast to move onshore with IVT >750 kg m-1 s-1 forecast over Northern California this evening.
  • Recent model runs have slowed the progression of this system, leading to increased duration of AR conditions along the coast and enhancing the potential for high-impact precipitation over California through the rest of this week.
  • The GEFS and ECMWF ensemble control members are forecasting AR 5/AR 3 conditions respectively along coastal Northern and Central California and AR 2/AR 3 conditions over coastal Southern California, although there is still uncertainty in the duration and intensity of AR conditions due to uncertainties in the progression of the cutoff low over the region.
  • The NWS Weather Prediction Center (WPC) is forecasting a broad region of 2–4 in. of precipitation over much of California, with areas of >4 in. forecast over the coastal ranges of Northern & Central California, along the Sierra Nevada, and in the Transverse Ranges. Model precipitation totals from the GFS and ECMWF are forecast to exceed 5-10% of annual rainfall over multiple catchments.
  • The NWS WPC has issued marginal risk (level 1 of 4; ≥5% probability of flash flooding) and slight risk (level 2 of 4; ≥15% probability of flash flooding) excessive rainfall outlooks (EROs) over Northern & Central California for 4 AM Wed 12 Nov–4 AM Fri 14 Nov and for Central & Southern California for 4 AM Fri 14 Nov–4 AM Sun 16 Nov to highlight the potential for flash flooding from this AR.
  • Freezing levels are forecast to remain relatively elevated during this AR due to the slow progression of the upper level cutoff and cold air behind the system, which will likely limit significant snowfall totals to the highest terrain along the Sierra Nevada.
  • Although this AR will bring beneficial precipitation to areas of Southern California that are currently experiencing drought, there is also an increased chance of localized flash flooding due to short-duration high-intensity precipitation and multi-day rainfall totals particularly over recent burn scars.

Click images to see loops of GFS IVT and 500 hPa Abs. Vort. forecasts

Valid 0000 UTC 12 November 2025 – 1200 UTC 16 November 2025

Summary provided by S. Bartlett, C. Castellano, M. Steen, S. Roj, B. Moore, J. Cordeira, and J. Kalansky, ; 12 November 2025

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