How Much Rain Will SoCal’s Atmospheric River Storm Bring? Risks Explained
An atmospheric river is set to impact Southern California this week, bringing with it notable amounts of rainfall and associated risks. Meteorologist Ryan Kittell from the National Weather Service in Oxnard has described the event as a long-duration storm expected to last for several hours across the region.
Rainfall Forecast and Timing
The storm is predicted to peak in Los Angeles during two main periods: Thursday night into early Friday and then again on Saturday. Saturday poses a particular challenge for forecasters due to uncertainty surrounding the storm’s track.
- Thursday: Rainfall will begin with about 0.1 to 0.2 inches expected across L.A. County, increasing to 0.75 to 1.5 inches overnight.
- Friday: Daytime rainfall is estimated at 0.5 to 1 inch for coasts and valleys and 0.75 to 2 inches in the mountains.
- Saturday: Additional rainfall of 0.5 to 1 inch expected during the day, with total accumulations possibly reaching up to 2.35 inches for coasts and valleys and 3 to 5 inches in mountainous regions.
- Sunday: As the storm dissipates, expected rainfall drops to 0.1 inch or less.
Evacuation Warnings and Risks
Evacuation warnings have been issued from 6 PM Thursday to 11 AM Sunday for areas near recent burn scars. This includes areas affected by the Palisades, Eaton, Kenneth, Sunset, and Hurst fires.
The potential for flash flooding and debris flows is significant, particularly on Saturday. Peak rainfall rates could reach up to 1 inch per hour, exceeding the critical threshold for triggering debris flows. Winds may also be a factor, with gusts reaching 50 mph in the Grapevine area.
Impacts on Traffic and Safety
Topanga Canyon Boulevard will close due to the risk of heavy debris flows, starting at 10 PM Thursday. This closure may extend into the weekend. The storm is also expected to impact traffic in Los Angeles and Ventura counties, leading to congestion and travel delays.
Significance for Fire Season
Forecasters note that widespread rainfall of 3 to 4 inches in lower elevations is typically required to effectively conclude the fire season. Downtown Los Angeles already recorded 1.38 inches of rain on October 14. The region experienced above-normal rainfall last winter, culminating in a significant storm event in February that contributed to ending the high-risk fire weather season.
This upcoming atmospheric river event could play a crucial role in mitigating fire risks in Southern California, contributing to the much-needed rainfall as the fire season winds down.
