Debris Flow — San Bernardino County Mountains, California

2010-12-20 · San Bernardino County Mountains, California

Event narrative

Highway 330, one of the main routes to Big Bear in the San Bernardino Mountains, collapsed near mile marker 35 on December 20. The force of the water coming down the mountain washed the hillside out from underneath the road itself, causing the collapse. Repairs to the road could take up to 2 years and $15 million.

Wider weather episode

A large Pacific plume of moisture ahead of an advancing trough of low pressure brought heavy rain and periods of serious flooding for nearly a week. The plume of moisture responsible was a form of an Atmospheric River. The mountain areas, particularly the San Bernardino range, experienced record large rainfall totals and many areas of flash flooding, debris flows and mud slides. Most rivers in the county warning area reached flood stage. Other effects include numerous traffic collisions, roadway flooding and closures, swift water rescues, beach closures and millions of dollars in damage to homes, businesses and infrastructure. Along with numerous city and governor-declared States of Emergency, President Obama proclaimed a Federal disaster declaration for 10 counties in California, including all four counties comprising the SGX CWA.

Source: NOAA Storm Events Database, event_id 272621. Narrative written by the NWS forecast office that issued the report.