CW3E AR Update: 13 March 2023 Outlook

March 13, 2023

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Strong Atmospheric River to Bring Additional Heavy Precipitation and Flooding to California

  • Another atmospheric river (AR) will impact California this evening into Wednesday
  • AR3 conditions (based on the Ralph et al. 2019 AR Scale) are forecast near Santa Cruz, CA, while AR2 conditions are forecast over much of the remainder of coastal California between Sonoma County and San Diego County
  • Strong upslope moisture flux will support heavy precipitation over the Sierra Nevada, Central California Coast Ranges, and Transverse Ranges
  • The NWS Weather Prediction Center (WPC) is forecasting at least 3–7 inches of precipitation in these areas over the next 3 days, as well as 1–3 inches of precipitation in the lower elevations of coastal Southern California
  • Moderate precipitation amounts of 1–3 inches are also forecast in the higher terrain of the Colorado River Basin due to inland penetration of the AR
  • Heavy rain falling in areas with saturated soil conditions and high river/stream levels will likely produce major hydrologic impacts throughout California
  • The NWS WPC has issued a moderate-to-high risk of rainfall exceeding flash flood guidance in the vicinity of the Sierra Nevada, Coast Ranges, and Transverse Ranges through Wednesday morning
  • The California–Nevada River Forecast Center is currently forecasting 13 stream gages to rise above flood stage over the next 5 days
  • Similar to the previous storm, freezing levels will be relatively high, and a majority of the precipitation is forecast to fall as rain in watersheds along the Sierra Nevada
  • Extreme winter storm impacts are expected in the higher terrain of the Sierra Nevada, where up to 5 feet of snow are possible

Click images to see loops of GFS IVT and IWV forecasts

Valid 1200 UTC 13 March – 1200 UTC 16 March 2023










Summary provided by C. Castellano, S. Bartlett, J. Kalansky, and S. Roj; 13 March 2023

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