Incoming New Year’s storm renews flood and debris flow threats in California

By CNN Meteorologist Briana Waxman, Chris Dolce

(CNN) — Another series of atmospheric river-enhanced storms will soak California as the new year begins, bringing a flood threat and evacuation warnings back to the state just days after a destructive Christmas-week storm.

The midweek storm lacks the extreme ingredients of last week’s flooding, but it arrives in a state already pushed to its limits. With soil having little room to absorb additional water, rainfall rates rather than totals will determine where problems emerge.

Southern California, including Los Angeles, is the area of most concern, but the rest of the state will see more rain that could slow down travel.

“Since the ground is so saturated from the super soaking Christmas storm, almost all rainfall will become runoff. This will allow flooding to occur with less rain amounts and rates than is typical,” the National Weather Service in Los Angeles said.

California Gov. Gavin Newsom prepositioned crews and equipment ahead of the rain to respond to flooding and debris flows in Los Angeles and Ventura counties.

Evacuation warnings have been issued for the second time in a week in parts of Los Angeles County recently burned by wildfires. The storms present a heightened threat of debris flows and flash flooding in these areas, which are the most incapable of absorbing heavy rain.

The voluntary warnings begin at 11 a.m. PT and are meant to give residents time to prepare with heaviest rain moving in Wednesday night.

Those warnings include the greater Wrightwood area, which was devastated by debris flows and flash flooding on Christmas Eve. Residents had to frantically flee their homes as a torrent of debris rushed through town and encased homes and cars in feet of mud.

No evacuations have been ordered for Wrightwood proper in San Bernardino County, but they are in effect just to its west across the county line in Los Angeles County.

The storm is expected to reach Southern California New Year’s Eve, then spread north through much of the state into New Year’s Day. Much of Southern California is in a Level 2 of 4 flooding rain threat Wednesday and Thursday, the Weather Prediction Center said.

Coastal and valley areas such as downtown Los Angeles could see 1 to 3 inches of rain, with 2 to 5 inches possible in foothills and mountains.

Light rain began in Southern California Wednesday morning, but the most worrisome downpours arrive around the stroke of midnight and will last through noon on New Year’s Day. Rainfall should ease through the afternoon hours.

The timing is bad news for the 137th Tournament of Roses Parade Thursday morning in Pasadena. This is expected to be the first wet Rose Parade since 2006, according to the National Weather Service.

Rain arriving Wednesday night will affect parade-goers camping along the route, with downpours continuing into Thursday morning.

This system is only the first of three in a conga line that could affect the waterlogged state through early next week.

Conditions change late Friday into Saturday as colder air drops snow below major pass levels, including Interstate 80 through Donner Pass.

Over a foot of snow is likely at Sierra Nevada ski resorts, though exact totals remain uncertain and could make mountain travel hazardous.

An avalanche last Friday killed a ski patroller and left another patroller injured at the Mammoth Mountain Ski Area in the eastern Sierra, according to the resort. It happened after feet of snow buried the mountain range last week.

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