USA – Atmospheric River Causes Floods and Mudflows in California

A convergence of strong Pacific storms – a “bomb cyclone” and an “atmospheric river” – triggered floods, mudflows and wind damage in California on 24 October. The storm also affected parts of Washington state and Oregon. Wind damage caused power outages affecting 400,000 people. Two people were killed when a tree fell on a vehicle near Preston, Washington.

Atmospheric River in California, USA, 23 October 2021. Image: NWS Prediction Center

As of 25 October parts of northern California were worst affected by the heavy rain. National Weather Service (NWS) Bay Area said downtown San Francisco saw its fourth wettest day ever, with 4.02″ / 102 mm of rain falling on 24 October, 2021.

Flooding was reported across the San Francisco Bay Area, including in Berkeley and Oakland. Swollen rivers caused flooding in Napa and Sonoma counties. Some homes were evacuated in Santa Rosa, Sonoma county, after several creeks broke their banks.

Landslides blocked a stretch of Highway 70 in Butte and Plumas counties after rain fell in areas of the Dixie Fire burn scar. Sections of Highways 16 and 20 were closed in due to mudslides in Colusa and Yolo counties.

Evacuation warnings or orders were issued in burn scar areas of parts of Fresno, San Mateo, Santa Cruz and Santa Barbara counties.

NWS Bay Area said the impact of the atmospheric river is edging southwards and, as of early 25 October was beginning to impact Monterey County.

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