Frigid air, snowstorm in store for the western US this week
An active weather pattern will unfold across the Northwest this week and usher in Arctic air and rounds of wintry weather.
AccuWeather meteorologists say an active weather pattern across the Western U.S. this week can pull in brisk, Arctic air and help produce areas of heavy mountain snow. In the upper levels of the atmosphere, the jet stream will begin to plunge southward during the first half of the week, which will help usher in a large storm to the Northwest.
Winter storm warnings are in place across the West, extending from the Washington Cascades to the Laguna and Cuyamaca Mountains east of San Diego.
Conditions across the West started off somewhat mild for many locations on Monday compared to the harsh cold that will arrive by midweek.
A fast-moving storm and its associated frontal boundary will swing through parts of the northern Rockies into the Upper Midwest and Great Lakes region from through the end of the day Tuesday. As this feature traverses across the northern tier of the Western and Central states, it will begin to pull chilly, Arctic air southward into the United States from Alberta and Saskatchewan.
Nature will start to give the West hints of what is to come, lowering temperatures on Tuesday across parts of Washington, Oregon, Idaho and Montana.
Another storm will follow closely behind the clipper storm, arriving in full force Tuesday in the Northwest. All eyes will be on this segment as it is expected to track southward and deepen as it brings cooler air, snow and gusty winds and as far south as the Four Corners.
By Tuesday night and Wednesday, disruptive high winds will shift into the Southwest, impacting many of the high deserts and mountainous regions of New Mexico, Arizona and Southern California. Gusty winds will even extend all the way to the coast, impacting the San Diego metro area with gusts as high as 50 mph.
Forecasters warn that strong winds across these areas on Monday and Tuesday can lead to travel slowdowns along area roadways and Interstates, such as Interstates 8, 10, 25 and 40. The strongest winds are likely to occur in portions of New Mexico and Arizona, where AccuWeather Local StormMax™ gusts near 100 mph are possible.
Occasional snowfall focused across the higher terrain of the northern Rockies Monday night. By Tuesday, periods of snow will reach southward into parts of Oregon, Northern and Central California, Nevada, Utah and Colorado while also persisting in the northern Rockies.
Several areas had already recorded 7 or more inches of snow as of Monday afternoon, including Battle Lake and Gillette, Wyoming. To the north in Montana, 5 inches of snow was observed near Hardin on Monday afternoon.
In Salt Lake City, rain showers are expected to change over to snow throughout Tuesday. Overnight on Tuesday, conditions will gradually transition over to periods of snow, which can persist through Wednesday and total 6-10 inches.
Stark temperature drops across interior West by midweek
As the storm plunges southward into parts of the Southwest late Tuesday into Wednesday, a dramatic temperature shift will occur from Montana to Utah and Colorado as brisk air is pulled from Canada.
"Temperature readings can drop quickly, likely falling between 20-40 degrees over 24 hours for most locations," said AccuWeather Meteorologist Brandon Buckingham.
In Billings, Montana, high temperatures on Wednesday may only reach -4 F, a noticeable difference from the expected Tuesday daytime high of 40 F. Similarly, in Casper, Wyoming, daytime highs from Tuesday to Wednesday can shift from 44 F to 4 F, with a Friday night low of -15 in the current forecast.
Other notable shifts in temperature from Tuesday to Wednesday can occur in Denver and Salt Lake City. Salt Lake City could observe a 24-hour temperature change of 17 F, while Denver can drop to around 29 F heading into midweek.
In the highest elevations of the Cascade Range, northern Rockies and Colorado Rockies, snowfall amounts can total up to 18-24 inches from Sunday to Wednesday with the AccuWeather Local StormMax™ of 60 inches.
Snow will continue to spread southward along the Sierra Nevada as well as mountains in Arizona and New Mexico through Wednesday night. In Arizona, the highest snowfall accumulations ranging from 6-12 inches are likely to dominate portions of the Kaibab Plateau, White Mountains and Mongollon Rim. Similarly, the highest peaks of the Sierra Nevada could observe amounts ranging from 6-12 inches from Tuesday to Wednesday.
Snow to dip to low levels in California
From Wednesday to Thursday, snow levels may dip to close to 1,500 feet in central California.
"This means that not only may some of the hills in the region receive a coating of snow, but snowflakes could make a rare appearance at some lower elevations," AccuWeather Senior Meteorologist Dave Houk said.
Since snow levels will dip to around 2,000 feet in Southern California, very hazardous road conditions are likely over the region's mountain passes Friday and Friday evening.
"Interstate 5 over The Grapevine, as well as Interstate 8 through the San Diego County mountains, are likely to see a period of very heavy snowfall and strong wind gusts. Travel is likely to become extremely difficult along these routes, and even road closures may occur," AccuWeather Meteorologist Andrew Johnson-Levine said.
Even Interstate 15, which is directed through Cajon Pass and is often at a low enough elevation to avoid snow, will not avoid wintry weather this time around. At least a few inches of snow can be expected here Friday night, adding to the logistical challenges that this storm may bring.
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Enough rain may fall at lower elevations in coastal Southern California from Thursday to Friday evening to make for slick roads as well as create incidents of flash flooding and debris flows. A general 1-4 inches of rain is likely with locally higher amounts over the lower south- and west-facing mountainsides.
Residents within the zone of the storm's impacts this week could face a variety of hazards ranging from blowing snow, wind-driven rain, difficult travel and road closures. Gusty winds could also raise the risk of vehicle blowovers, particularly with high-profile vehicles.
As this feature gradually tracks east of the Rocky Mountains from mid-to late week, it will continue to spread a swath of snow and the threat for ice from the Great Lakes to areas of the Northeast.
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