Storm to heighten flooding, mudslide risk in fire-scarred Southern California

By Renee Duff, AccuWeather meteorologist
January 09, 2018, 3:07:49 PM EST

A powerful storm will plow into California with heavy rain, mountain snow, gusty winds and a significant mudslide threat into Tuesday night.

“This storm will be significant for Southern California due to the dry start to the rainy season,” AccuWeather Meteorologist Jordan Root said.

The risk of fast-moving mudslides and debris flows will be high given the amount and intensity of rainfall expected over recent burn-scar locations.

SoCal Storm 1.9 AM

Ahead of the storm, evacuations were ordered for the Thomas, Whittier, Sherpa and Rey fire burn scars, Santa Barbara County officials announced in a press release on Sunday.

The Thomas Fire, which is California’s largest wildfire on record, has left nearly 282,000 acres of charred land in its wake. Containment on the fire stands at 92 percent.

Mandatory evacuations were ordered on Monday afternoon for areas impacted by the Creek Fire near Sylmar, California as rain moved through the region.

“A connection of tropical moisture will be present and will help aid in bringing heavy rain to parts of the state,” Root said.

Los Angeles and other Southern California cities may pick up an inch or more of rain, which would make it the biggest rainstorm since last February.

“The foothill and mountain areas, especially areas facing south and west, will receive the heaviest rain with 3 to 6 inches possible,” Root said. “This may lead to flooding and debris flows, especially near burn-scar areas.”

Santa Barbara, Ventura and Los Angeles counties will face the heaviest rainfall into Tuesday afternoon.

Static Tuesday SW

Heavy rain fell on Northern California into early Tuesday morning with approximately 3.50 inches of rain falling on San Francisco and Sacramento.

While rainfall is forecast to be more sporadic over Northern California for the balance of the storm, heavy rain will focus on Southern California for the storm's duration into Tuesday night.

Motorists should slow down to lower the risk of hydroplaning and be on the lookout for road washouts and debris flows.

Damage and road closures were reported around Santa Barbara County early Tuesday morning, according to local officials. A mudslide has closed a stretch of U.S. Highway 101 in Montecito with people reportedly trapped in their cars, according to NBC Los Angeles.

Thunderstorms with small hail and frequent lightning are not out of the question, especially across central and southern portions of the state. Brief waterspouts can form over the coastal waters and spread inland for a time.

Gusty winds will continue to kick up along the coast and over the mountains as the storm approaches and swings inland, according to AccuWeather Senior Meteorologist Ken Clark. Sporadic power outages are possible. Gusts between 50 and 75 mph have occurred over the Coast Ranges.

Into Tuesday night, soaking rain, along with gusty winds, will spread into the Desert Southwest, including in Las Vegas and Phoenix. Localized flash flooding is possible in the arid landscape.

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“While there will be plenty of negatives with this storm, it will also prove to be beneficial as it will provide some much-needed rain,” Root said.

All of Southern California is abnormally dry or experiencing a moderate drought, according to the United States Drought Monitor. Conditions have been even drier across the Four Corners region, where severe drought is occurring.

The rainfall will put a dent in precipitation deficits, as well as put an end to the wildfire season.

Heavy snow piling up in the highest terrain of the Sierra Nevada will be a boost to the ski industry and California’s water supply for the coming summer.

This past week, measurements by California’s Department of Water Resources revealed that the Sierra Nevada snowpack is around 3 percent of normal for this point in the winter season, according to the Associated Press.

As the storm pushes inland, locally heavy snow will spread across the various ranges of the Intermountain West into Wednesday.

Static Rockies Snow Through Wednesday

This storm will not mark the start of a stormier pattern in the Southwest.

In the wake of the storm a weak to moderate Santa Ana event is likely prior to the end of the week. However, with wet fuels this time around, the risk of new wildfire ignition is minimal.

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