CW3E Event Summary: 9-15 March 2023

20 March 2023

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Atmospheric Rivers Produce Heavy Precipitation and Flooding in California

• Two atmospheric rivers (ARs) made landfall over California during 9–15 Mar
• These ARs were characterized by the transport of very warm, moist air from the tropical North Pacific into the midlatitudes
• The first AR brought AR3 conditions (based on the Ralph et al. 2019 AR Scale) and IVT magnitudes > 750 kg m^-1 s^-1 to Monterey and Santa Cruz Counties
• The second AR brought AR2 conditions and IVT magnitudes > 500 kg m^-1 s^-1 to Central and Southern California
• The heaviest precipitation fell during the first AR in the Central and Southern Sierra Nevada, with some locations recording > 12 inches in a 3-day period and sustained precipitation rates > 0.5 inches/hour
• High freezing levels limited snowfall accumulations below 7,000 feet in both storms
• Snow survey stations located above 7,000 feet recorded 7-day SWE increases > 12 inches
• High reservoir inflows prompted dam operators to open the main spillway and increase releases to > 15,000 cfs at Oroville Dam after the first AR
• The combination of heavy rainfall and melting snowpack led to widespread riverine flooding across Northern and Central California
• The most destructive flooding occurred along the Pajaro River in the community of Pajaro, CA, and along the Kern River in Kernville, CA
• An EF-1 tornado caused structural damage to mobile homes and farms in Tuolumne County

Click images to see loops of GFS IVT/IWV analyses Valid 0000 UTC 9 March – 0000 UTC 16 March 2023

Summary provided by C. Castellano, S. Bartlett, S. Roj, and J. Kalansky; 20 Mar 2023

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