By AccuWeather Meteorologist
Published Dec. 26, 2021 1:18 PM EST | Updated Dec. 27, 2021 9:26 PM EST
The onslaught of storms that have marched into the western United States has undoubtedly created headaches for travelers and residents at times, but it has also proven to be very beneficial in building up an expansive snowpack across most mountain ranges in the region. Looking ahead to the final week of 2021, the cold and unsettled weather regime is expected to continue.
The stormy pattern across California has been a blessing for easing drought concerns so far this fall and winter, with the entire Sierra Nevada Mountain Range now running above historical snowpack averages. With consistently cold conditions slated to remain anchored over the mountains, those numbers will continue to rise as the calendar turns to 2022.
Reservoir levels across the lower terrain and foothills of California have also continued to experience an uptick in water levels, as consistently stormy weather has bumped levels upward.
Farther north across Washington's Cascade Mountain Range, most basins are within 10-20% of their historical snow water equivalent at this point in the season.
While the consistently unsettled weather regime has greatly benefited the mountain ranges, it has also resulted in numerous weather-related headaches for residents that reside at lower elevations.
Both Los Angeles and San Francisco have observed around 200% of average rainfall so far this month, resulting in episodes of flash flooding and travel nightmares at times. Through Dec. 25, San Francisco has had 14 days with measurable precipitation, tallying up a whopping 8.57 inches.
Across the Southwest, places like Flagstaff and Phoenix, Arizona, have experienced their fair share of wet weather as well, as both cities observed an inch or more of precipitation on Christmas Eve.
Looking ahead, there's more on the way across the West.
Winter weather advisories as well as winter storm watches and warnings are in place across a wide swath of the western United States as of Sunday, Dec. 26.
Record-challenging cold weather will remain in place across the Northwest early this week, resulting in impressively low snow levels. In some locales Sunday morning, snow was reported down to sea level in Washington.
Heavy snow was reported in the Seattle metropolitan area during the pre-dawn hours on Sunday and snow continued throughout much of the day.
Snow dealt a severe blow to operations at the Seattle-Tacoma International Airport on Sunday. At one point Sunday afternoon, more than 360 flight delays and almost 290 cancellations were reported as crews worked around the clock to clear runways and deice aircraft.
"Snow totals for the Seattle area ended up being generally on the order of 2-4 inches on Sunday, with northern areas experiencing locally higher accumulations," AccuWeather Meteorologist Mary Gilbert said.
The Emerald City averages around 6.8 inches of snowfall per year.
Another storm may bring a chance for additional snowflakes Wednesday night through Thursday night, but milder air may limit any chances for accumulations in the city itself.
A similar snowy scene is expected to extend down the Interstate 5 corridor from Washington southward through Oregon into Northern California into Monday night.
As the storm shifts southward early this week, another burst of heavy snow will sweep into the mountainous terrain of California, piling up feet of snow across the Sierra Nevada. Extremely difficult, if not impossible travel conditions are likely along most mountain pass roads including Donner, Echo, Carson, Sonora and Tioga passes.
"The heavy snow will continue to create travel and logistical challenges across the passes as this will lead to another round of pass closures and the need for chains on most vehicles. This includes those who are traveling back from the holidays or are traveling to the ski resorts," AccuWeather Senior Meteorologist Tyler Roys explained.
Snow levels fell throughout the day on Monday across Central and Northern California from around 2,000 feet. Snow levels could go down to as low as a few hundred feet by Monday night, making for difficult travel along roadways that normally do not deal with wintry conditions.
While the heaviest snow on Monday will occur across the Sierra Nevada, wintry conditions will not be limited to just the states bordering the Pacific Ocean. A plume of moisture will stream into the Intermountain West, bringing along snow to places like Idaho's Snake River Valley, Salt Lake City and into the mountainous terrain of western Wyoming.
On Monday, the snow caused power outages across portions of California, including Nevada City. The heavy snowfall there knocked trees into power lines, leaving homes and businesses without power.
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The storm will continue to shift southeastward into the Four Corners Region by Monday night. The high terrain of Utah's southern Wasatch Range, Arizona's Grand Canyon and Mogollan Rim and New Mexico's Colorado Plateau and Sangro de Cristo Mountains can all expect a fresh blanket of snow before conditions briefly settle down by midweek.
This storm won't be the only weather-maker to talk about across the West either, as the active pattern will continue with another storm moving into Oregon and California on Tuesday. Again with cold air in place, impressively low snow levels are expected.
While the cold and snowy pattern has ski-lovers jumping for joy, the fresh powder will come along with hidden dangers. A major risk for avalanches is expected as a result of the rounds of snowfall across the mountainous terrain. For the thrill-seekers looking to get out into the back country, this is risk is especially dangerous and proper precautions should be exercised.
From midweek into the upcoming weekend, the storm slated to bring another round of wet and snowy weather is expected to pivot southward along the West Coast, bringing a renewed threat across the lower terrain for flooding to California and the Southwest as well as feet of snow in the mountainous terrain. On top of that, yet another storm is expected to usher in rain and snow across the Northwest between Thursday and Friday.
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