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The first significant storm of the winter season may bring drenching rain and heavy mountain snow to the southwestern United States, including Southern California, early this week.
The weather pattern began to change across the region during the first few days of 2018 as a small amount of moisture began to flow in from the Pacific Ocean and into California.
"More rain fell from Wednesday to Friday night (0.52 of an inch) in San Francisco than during all of December (0.07 of an inch)," AccuWeather Meteorologist Renee Duff said.
This trend will continue and is poised to ramp up as a storm affects California and much of the Southwest spanning Monday through Tuesday night.
The new storm has the potential to bring an inch or more of rain to Los Angeles and other areas along the Southern California coast.
Heavy rain is in store along the western- and southern-facing slopes of the mountains. Several inches of rain may fall on these areas.
It may be the biggest rainstorm since last February for Southern California.
"Should that amount of rain materialize, it is enough to raise the risk of flash and urban flooding in Southern California from Monday night to Tuesday night," according to AccuWeather Senior Meteorologist Ken Clark.
Ahead of the storm, evacuations have been ordered for the Thomas, Whittier, Sherpa and Rey fire burn scars, Santa Barbara County officials announced in a press release on Sunday.
The last time downtown Los Angeles received measurable rain (0.01 of an inch or greater) was on Nov. 17. The last time there was 0.10 of an inch of rain in the city was Oct. 20.
Rainfall typically ramps up during the autumn and peaks during the middle of the winter in coastal Southern California. On average, 2.33 inches of rain falls on Downtown Los Angeles during December, with 3.12 inches in January, 4.17 inches in February and 2.43 inches in March.
The latest United States Drought Monitor report places much of Southern California in abnormally dry to moderate drought conditions.
Many locations in Northern California have received sub-par rainfall since September as well. Both San Francisco and Sacramento have received less than 50 percent of their average rainfall of 8 and 7 inches, respectively.
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The storm is likely to spread at least some rain over much of the lower elevations of California, Nevada, Utah and Arizona.
The major cities of San Francisco, San Diego and Sacramento are all likely to get a soaking from the storm. Some rain is also expected in Las Vegas, Phoenix and Salt Lake City.
"In addition to the risk of flooding, mudslides may occur with the greatest risk in recent burn scar locations," Clark said.
At particular risk is the massive scar left behind from the Thomas Fire, which is still active but 92 percent contained. The Thomas Fire is the largest wildfire on record in California and has charred close to 282,000 acres, according to Inciweb.
Despite the risk of debris flows, any non-destructive rainfall will be welcomed and should finally bring an end to the wildfire season in Southern California. Recent rainfall has ended the wildfire danger in Northern California.
Heavy snow is likely in the Sierra Nevada and the various mountain ranges that riddle the Southwest as the storm moves inland.
The snowiest places in the high country may receive a couple of feet of snow.
The snow will be a boost for the ski resorts in the region, which have seen little to no snow so far this season.
A change from rain to snow is expected to create slow travel over I-80's Donner Pass in California Monday night into Tuesday. Snow levels may dip as low as Cajon and Tejon passes in Southern California at the tail-end of the storm as well.
"The storm will kick up gusty winds along the coast and over the mountains as the storm approaches and swings inland," Clark said. The gusty winds will spread to the deserts on Tuesday.
In the wake of the storm, showers may linger in parts of Northern California at midweek. However, dry weather is expected to return for another stretch until perhaps the middle of the month.
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