Evacuations ordered as L.A., Southern California and Southwest brace for heavy rain, mudslides
Several inches of rain will soak Los Angeles and Southern California as a Pacific storm strengthens with the risk of flash flooding, debris flows, and travel delays expanding inland over the Southwest.
AccuWeather’s Ken Clark says a powerful storm system from the Pacific will bring drenching rainfall and an increased risk of flash flooding and mudslides to Southern California this weekend.
Another round of heavy rain is expected across Southern California and parts of the Southwest, including Los Angeles, as a storm strengthens this weekend. AccuWeather meteorologists warn that torrential rain could lead to flash flooding, mudslides and washed-out roads, making travel difficult or dangerous.
The bulk of the rain will focus on the southern half of California and will spread inland over the deserts in Nevada, southeastern California and Arizona. In the central part of the state, rain may return after a lull during the weekend.
Evacuation orders have been issued in areas around burn scars from recent wildfires, including the Eaton Fire and Palisades Fire.
Near the apex of the storm, around Los Angeles, 2-4 inches of rain is forecast from Friday night to Sunday. Some parts of the Los Angeles area are expected to receive close to 6 inches of rain.
South- and west-facing mountainsides along the coast could receive 6-10 inches of rain from both parts of the storm.
Rapid runoff on steep terrain will likely cause flash flooding, mudslides and debris flows. As of Saturday morning, there have already been reports of mudslides in Santa Barbara County. Some roads may be washed out or become impassable. The heaviest rain is forecast to fall on Saturday evening in the greater Los Angeles area.
Some hillsides may become unstable due to the weight of the water and slippery topsoil on top of the bedrock in the days that follow.
The expected rainfall is three to six times the region’s historical November average and could rival some of the biggest winter storms of recent years. Rainfall from this storm alone may account for one-quarter to one-third of the region's entire annual historical rainfall.
Some media sources have described the storm as an atmospheric river. AccuWeather meteorologists analyze a great deal of data to make that determination, including the length of the moisture plume that develops over the Pacific and extends inland.
This moisture stream is shorter and on the lower end of the atmospheric river scale. A medium- to high-end atmospheric river is not needed to produce torrential rainfall and widespread flooding.
During an Atmospheric River, narrow columns of tropical moisture cause enhanced rain and snow for the western U.S.
The threat of torrential rain and flash flooding will extend beyond Los Angeles and the Transverse Ranges into the deserts of Southern California. San Diego, Santa Barbara, San Bernardino and Palm Springs, California, are among the major cities in the southern part of the state at risk for travel disruptions, damage and dangerous conditions from the storm.
Heavy rain may even reach Death Valley, bringing the risk of washouts on roads that traverse the remote national park.
Las Vegas, as well as Yuma and Flagstaff, Arizona, are forecast to receive one or more rounds of heavy rain and flooding issues this weekend.
Some areas will also experience thunderstorms, a few of which could become severe with damaging wind gusts or hail. Isolated waterspouts or brief tornadoes could occur from the strongest storms.
Motorists should avoid driving through flooded roads. The water may rise rapidly or be much deeper than it appears, causing vehicles to stall. The road surface may have been washed away or weakened due to the high water.
As colder air moves in, higher elevations in Southern and Central California are expected to receive several inches of snow. A couple of feet of snow may blanket the ridges and peaks in the Sierra Nevada and other high ranges in the region. However, snow levels will remain above pass elevations.
Depending on the number and intensity of the storms, the month may end up among the wettest Novembers in terms of rainfall.
Another storm will drop southward along the California coast from Sunday night to Monday. At this time, the rain with this storm will be significantly less intense and more intermittent for most areas. However, there can be a few locations that pick up an inch or two of rain near the coast, which may aggravate the flash flooding and debris flow situation and cleanup. Snow levels with this storm will dip to pass levels in the Sierra Nevada.
After a period of dry weather following the Monday storm, additional storms may track into California later in the month.
The storm this weekend alone will help ease drought conditions in the Southwest, as significant rain is expected to fall on parts of the Colorado River basin. However, many more storms will be needed to reverse the decline in water levels on lakes Mead and Powell.
Meanwhile, water levels in many of California's reservoirs are at normal to above-normal capacity for mid-November. The rain and moist vegetation will knock down the wildfire potential in the short term.
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