Pre-Christmas storm with rain, wind and snow to roll into western US

By Alex Sosnowski, AccuWeather senior meteorologist

December 20,2016, 12:00:57PM,EST

 

 

A pre-Christmas storm with rain, wind and mountain snow will affect much of the western United States.

While the storm will bring another dose of drought-denting rain and dump more snow onto the ski slopes, it has the potential to cause major travel disruptions.
Enough rain can fall on the urban areas of California to cause sporadic flash flooding. Motorists should allow extra time to travel and reduce their speed on area highways and city streets. Airline delays are likely at the major hubs.
Drenching rain will first arrive in southern Oregon and northern California early on Friday morning.

From there, precipitation will push southward and inland during Friday midday, afternoon and night.
A thorough soaking is in store for San Francisco and much of the Bay Area, as well as Sacramento, California, and Medford, Oregon.
The storm will bring a period of drenching rain across much of Southern California as well. Areas from San Bernardino and Los Angeles to San Diego could be hit with heavy rain on Friday night into Saturday morning. Spotty rain showers may linger into Saturday afternoon.
Showers will also reach the deserts from Palm Springs, California, to Las Vegas and Phoenix on Saturday.
As the moisture encounters the mountains, it will be released in the form of accumulating snow.
As the storm advances Friday night and Saturday, colder air will be drawn inland and southward, according to AccuWeather Senior Meteorologist Henry Margusity.

"The advancing colder air will cause snow levels to lower to or below pass levels such as Siskiyou Summit along Interstate 5, Donner Pass along I-80, Cajon Pass along I-15 and Tejon Pass along I-5," Margusity said.
Motorists heading over these passes should make sure their vehicle is equipped to handle slippery, snowcovered roads.
From 1 to 2 feet of snow is likely to fall on the high country of the Sierra Nevada and southern Cascades from Friday into Saturday.
The storm will also bring significant precipitation across the Intermountain West during Friday night and Saturday. The same cold air invasion from California and Oregon will cause a rain/snow mix in valley locations to transition to snow.
Up to a few inches of snow can accumulate in the basins and valleys from northern Nevada to much of Utah and southern Idaho. Local amounts topping a foot are likely over the Wasatch Range and the Uinta Mountains.
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A little snow can also fall on the mountains of northern Arizona and New Mexico with enough to make for slippery travel along portions of I-40.
The storm will also pack gusty winds along the coast and over the mountains. Seas will be rough for a time Friday night into Saturday.
Strong winds will advance inland over the passes and are likely to cause blowing and drifting snow. The strongest winds will occur across the desert areas of New Mexico and Texas during Saturday night and Christmas Day.

By Christmas Day, the same storm will spread snow and wind to the eastern slopes of the Rockies and northern Plains with difficult travel conditions likely from Denver to Minneapolis.