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Fox News Weather Center

Chilliest Air Since Last April to Unload Mountain Snow in Western US This Week

Dramatically cooler air will sweep through the West and will be accompanied by accumulating snow in some locations.

Rain, Mountain Snow and Strong Winds Across the West

Temperatures will plunge 15-30 degrees Fahrenheit over much of the interior West as the leading edge of the cool air arrives.

Preceding the arrival of the chilly air will be gusty winds that can kick up dust from the deserts of California to the high plains of eastern Wyoming. The dust can cause sudden low visibility.

In many areas, the chilly air outbreak will deliver the lowest temperatures since last spring.

The list of cities that will experience their chilliest air in months includes Los Angeles and Sacramento, California; Phoenix and Flagstaff, Arizona; Las Vegas; Salt Lake City; Portland and Pendleton, Oregon; Seattle and Spokane, Washington; Boise and Pocatello, Idaho; Missoula and Great Falls, Montana; Jackson, Wyoming; and Aspen, Colorado.

The weather pattern will bring the coldest nights and the chilliest days since April in many locations.

Nighttime temperatures will dip well down into the teens and 20s in the mountains and deserts from Montana and Idaho to northern Arizona.

On the coldest days, temperatures will be held to the 30s in the mountains and in some of the northern high desert areas of the Great Basin.

Along with the outbreak will be areas of snow.

According to AccuWeather Senior Meteorologist Brian Wimer, snow will be mostly confined to the higher elevations of the southern Sierra Nevada, Wasatch Range and Rockies through midweek.

"Enough snow can fall over the higher passes to make roads slushy and snow-covered. Up to a foot of snow is forecast over the highest elevations," Wimer said. "However, enough snow can reach the valley floors in northern Nevada and Utah and in the lower elevations in Montana to whiten non-paved surfaces."

Snow will impact Donner Pass along Interstate-80 into Tuesday. Most of the snow is over in the northern Cascades, including along I-90.

The snow will tend to melt as it falls on the pavement along much of I-80 in Nevada through the middle of the week.

Farther east, road surfaces can get slippery over the higher terrain along I-15 in Utah, Idaho and Montana, I-70 in Colorado and I-80 in Utah and western Wyoming during the middle days of the week.

Motorists should be alert for areas of black ice over the mountains and colder valleys at night, even where rain fell during the day.

The air is not likely to get cold enough for snow to fall on Cajon and Tejon passes in Southern California and in the Denver metro area.

Mostly rain is in store for I-40 in Arizona. However, there may be snow showers at the tail end of the storm on Wednesday, which could cause slippery spots at night.

The mountains of northern New Mexico, which received some snow late last week, could get a bit more snow late this week.

According to AccuWeather Senior Meteorologist Ken Clark, "While the snow will be significant in the Sierra Nevada, it will be a drop in the bucket compared to what is needed."

The high country of the Sierra Nevada receives an average of 300 to 500 inches of snow per year according to the Central Sierra Snow Laboratory.

Snowfall in recent years has been much less than average and above-average temperatures have greatly reduced the existing snowpack. Sierra Nevada snowpack was determined to be the lowest in 500 years on April 1, 2015.

Approximately 30 percent of California's water supply originates from the Sierra Nevada snowpack.

Enough snow to cover a three-story building or more will have to fall on the Sierra Nevada and Cascades this winter to have a significant impact on the drought.

"At least the storm this week is a small step in the right direction," Clark said.