March 14 (UPI) -- It's way too early to write winter off in the western United States as a combination of an injection of Arctic air and a developing storm will set the stage for soaking coastal rain, travel-snarling snow and frigid conditions.
A push of Arctic air will invade the northern Rockies and interior Northwest this weekend.
Even though the surge of Arctic air appears to be more gradual than some blasts that have invaded the region in years past, by the middle of this weekend, some locations will measure temperatures 50 degrees to 70 degrees Fahrenheit lower when compared to midweek highs.
Factoring in AccuWeather RealFeel Temperatures, the nighttime hours may feel as much as 80 degrees colder when compared to Wednesday afternoon in Montana, northeastern Idaho and northern Wyoming, with values plummeting well below zero in these areas.
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But even near the coast, where places such as Portland, Ore., had a high near 60 at midweek, actual temperatures are forecast to dip into the middle 20s at night this weekend, when some snowflakes may be flying.
Freezing levels will plunge to most valley floors across the interior Northwest and are likely to end up within a couple hundred feet around Puget Sound, Wash.
Travel over the passes will become slippery and difficult. Blizzard conditions can occur for a time, including Lookout, Homestake and Bozeman passes in Montana along Interstate 90, as well as Marias Pass, along U.S. Route 2 in Montana.
Several inches of snow is forecast in Spokane, Wash. Meanwhile, Great Falls, Mont., can expect a foot or more of snow to pile up over the weekend.
"This particular setup may deprive the Washington and Oregon Cascades of more than a foot of snow, but the eastern slopes of the northern Rockies, and especially the Sierra Nevada, can pick up several feet of snow from the storm," AccuWeather chief on-air meteorologist Bernie Rayno said.
The heavy and sudden amount of snow over the high country will raise the risk of avalanches.
It is possible that I-80 at Donner Pass, Calif., may close for a time due to heavy snow and blizzard conditions.
The pattern that continues into early next week over California may end up being a "March miracle" in terms of precipitation, especially with the potential for 3 feet to 5 feet of snow to fall on the high country through Tuesday.
The Sierra Nevada got off to a good start with early-season heavy snowfall events from November to December. However, most of January and February were void of snow, resulting in a large snowfall deficit for the mountain range.
At the end of February, a survey conducted by the Department of Water Resources at the Phillips Station in the Sierra Nevada of California revealed a mere 29 inches of snow depth with a water equivalent of 11.5 inches. This was less than 50 percent of average for the season so far.
Rain will spread southward along the Pacific coast as the storm spins just offshore.
"The storm should deliver a thorough soaking to most coastal areas from Oregon this weekend through Northern California early next week," Rayno said.
"For these coastal areas, we are probably looking at a general 0.50 of an inch to an inch of rain with locally higher amounts, especially on mountainsides, in the lower elevations," he added.
The rainfall is especially important for Northern California as a storm bypassed the region and aimed at Southern California this past week. Areas over the southern third of the state picked up between 0.50 of an inch and 2 inches of rain.
Rain and mountain snow are forecast to spread into Southern California during the middle and latter part of next week as well. Rainfall may be similar to that of Northern California or greater.
"It does look like freezing levels will dip enough over Southern California for snow to fall on Cajon and Tejon passes during the second half of the week," Rayno said.
Once the storm pivots toward Southern California, rain and high country snow will spread inland well over the Southwest late next week. The new storm is likely to unleash a second soaking in a week's time. The storm that affected the Southwest this past week deposited about 0.31 of an inch of rain in Tucson, Ariz., to 1.28 inches of rain in Las Vegas and 2.18 inches of rain in Yuma, Ariz.
As stormy and cold weather lingers in the West, one or more large outbreaks of severe weather may unfold over the Central states, where warm and humid air is likely to surge northward later next week.
