One of the coldest storms of the winter with rain, low snow levels and thunderstorms will roll across California and the deserts and mountains of the Southwest through the middle of the week, threatening major travel disruptions.
The storm began to impact northern California Monday night, but the greatest impact in Southern California is coming late Tuesday and Tuesday night.
The storm will then swing eastward across Nevada, Arizona, Utah, New Mexico and Colorado Tuesday night and Wednesday with temperatures plunging to very chilly levels.
Temperatures will be slashed by 20 to 30 degrees in many locations of the Southwest U.S., when compared to highs from the past weekend.
The storm is expected to eventually affect a large part of the nation through the week with adverse weather conditions ranging from snow and ice to rain and severe thunderstorms.
The storm will bring snow and slippery travel to the Grapevine, other passes and the high deserts. Some of these roads may close for a time, due to sudden heavy snow and whiteout conditions.
There is the potential for people to get stuck venturing over the passes of Southern California Tuesday evening.
With this setup, snow can cap the coast ranges throughout California.
According to Western Weather Expert Ken Clark, "Snow will mix in as low as 2,000 feet in northern California and to 2,500 feet in southern California with several inches of snow as low as 3,000 feet."
A foot of snow can fall on the resorts in the northern Sierra Nevada with 1 to 2 feet of snow in the southern Sierra Nevada.
"The greatest impacts will be the Grapevine, Highway 14 through Soledad Canyon, I-8 across southern San Diego County and some of the higher passes on I-15 before Primm," according to Clark.
While the storm is not likely to unload a half a foot of rain, it can bring enough rain to be of benefit for the drought situation. Moisture will reach the deserts.
"On average, from one-third to two-thirds of an inch of cold rain is forecast to fall in the central and northern areas of California with one-half to one inch of rain in Southern California," Clark said.
Unfortunately, much of the rain will fall during a 6- to 12-hour period, which can cause flash and urban flooding. There could be a few incidents of mudslides (debris flows).
Gusty winds will kick up dust over the deserts ahead of the rain Monday night and Tuesday.
Snow can mix in around Las Vegas with the cold storm Tuesday night. Up to a half a foot of snow can fall on Salt Lake City with a foot or more possible in the Wasatch Range.
"A foot of snow or more is possible over Rim Country at elevations at and above 6,500 feet with several inches of snow around 5,000 feet," Clark stated.
Overall, snow levels in Arizona will drop to around 3,000 feet with several inches and slippery travel just above that level.
Motorists should expect difficult travel along I-40 Tuesday night and Wednesday and may want to select a more southern route as heavy snow will also fall across the mountains of northern New Mexico.
Other major routes affected include I-5, I-15, I-17, I-70 and I-80 in the Southwest U.S.
There should be more than enough rain to settle the dust in the desert areas. With very little moisture over the winter, any rainfall will be welcomed.
One-quarter to one-half of an inch of rain on average is expected in the deserts.
During the middle of the week, the storm will also swing farther east over the Colorado Rockies and Great Plains.
A blizzard could affect areas from the central Rockies to the central Plains Wednesday night into Thursday. There is also the risk of a major severe weather outbreak over the southern Plains and lower Mississippi Valley.
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