Atmospheric river could snarl travel in the West as Christmas approaches
By
Jessica Storm, AccuWeather Meteorologist
Published Dec 19, 2021 7:15 AM EDT
|
Updated Dec 21, 2021 6:21 AM EDT
An atmospheric river, or a plume of tropical moisture in the atmosphere, is expected to build into the western coast of the United States this week, bringing inordinate amounts of rain and snow to the drought-weary West and impacting travel as Christmas grows near.
Rain and snow have been slamming the Northwest this weekend, particularly around Portland and Pendleton, Oregon, where thick snowflakes were falling across portions of Clark, Multnomah and Clackamas counties on Saturday night and Sunday morning. Rain fell at Santiam Junction, as shown on highway cameras.
Flakes were sticking to cars and grass in Vancouver, Washington, but melted upon contact with roadways, while heavy snowfall was filmed in the Corbett area of Multnomah County, causing roads to become slick. Portland also recorded its first measurable snowfall of the season with 0.2 of an inch as of Sunday morning, before the city even fell below freezing.
Camp Bonneville, Washington, recorded 4 inches of snow as of early Sunday morning, with Camas, Washington, not too far behind with 2.8 inches of snow. By Sunday afternoon, a total of 18 inches of snow had fallen in Lucerne, Washington, with several other locations reporting above a foot.
Heavy rain caused the Marys River near Philomath, Oregon, to approach major flooding stage on Monday evening, which typically results in lowland and agricultural flooding, according to the NWS.
Earlier last week, the Southwest also had its fair share of precipitation as moisture moved onshore and brought over 3 inches of rain to San Francisco in one day on Dec. 13. Los Angeles International Airport reported over an inch of rain the following day, Dec. 14, while downtown received over 2 inches.
The storm track delivering this precipitation continued to target the northern half of the West on Sunday as most of the Southwest experienced dry conditions.
The opposite was true across the Northwest as valley rain and mountain snow continued to fall on Sunday. Rain continued in Portland and Eugene, Oregon, while snow fell late Sunday in Great Falls and Bozeman, Montana. From there, the focus of rain and snow began to vary each day and meander north and south.
Precipitation shifted northward on Monday and encompassed parts of northern Oregon and southern Washington.
Rain drenched parts of the Oregon and Washington coasts as snow (blue) fell over the interior and reached portions of northern Idaho and western Montana, on Monday, Dec. 20, 2021. (AccuWeather)
On Tuesday, the storm track is then forecast to shift southward, returning the focus of precipitation to the Southwest, but there can still be some lingering snow and rain in the coastal Northwest early in the week.
"The storm still spinning offshore will send another cold front toward the coast," AccuWeather Meteorologist Ryan Adamson said.
On Wednesday evening, a major storm is likely to begin across the West, producing rain and snow from Washington to Southern California.
"A sharp dip in the jet stream later this week will set the stage for a building atmospheric river into the West," said AccuWeather Senior Meteorologist Matt Rinde.
Cities in California like Redding, Sacramento, San Francisco, Fresno and Los Angeles can all experience 1-2 inches of rainfall from Wednesday afternoon through Saturday morning, with higher amounts in the mountains where temperatures are high enough for rain to fall.
"This pattern will lead to another round of heavy rain and mountain snow for the region," said Rinde.
AccuWeather Storm Warning Meteorologists are forecasting up to two feet of snow in the Cascades and 2-4 feet of snow across the Sierra Nevada from Tuesday evening to Saturday.
Such heavy precipitation could cause local flash flooding along with mudslides in burn scar areas, disrupting travel and producing extra traffic for shoppers. This could also delay last-minute packages before Christmas arrives. Motorists are urged to use caution and plan extra time to travel to their destinations.
CLICK HERE FOR THE FREE ACCUWEATHER APP
A winter storm watch has been issued for the Sierra Nevada Mountains through Sunday, warning commuters of difficult to impossible travel. Heavy snow can cause damage to trees and power lines across the area. By Monday evening, this had been upgraded to a winter storm warning in many areas in effect through the weekend.
"While this may be disruptive for holiday travelers, this is still a much-needed event for the region given the short-fall of rain for the last several years," Rinde said.
Nearly half of the West, which is comprised of Washington, Oregon, California, Nevada, Idaho, Montana, Utah, Arizona and New Mexico by the United States Drought Monitor, is in extreme drought. In fact, the only part of this region that is not at least abnormally dry is the far Northwest, where heavy rain flooded western Washington and northwestern Oregon earlier in the season.
Drought conditions are particularly bad across Central and Southern California, where over 80% of the state is in extreme drought and nearly a third in exceptional drought. Since the beginning of 2021, Los Angeles has only had 55% of its average precipitation, with Palmdale, California, at only a quarter of its yearly normal as the year approaches its end. Palm Springs, California, also makes the list with a third of its yearly average.
The storm may also drag enough cold air into the Northwest to drop snow levels below 1,000 feet in elevation, potentially bringing wintry weather to places like Seattle and Portland during the Christmas weekend, according to the long-range team.
"Air originating from Siberia will push southward across Alberta and southwestward across British Columbia Canada," AccuWeather Senior Meteorologist Brett Anderson said and added that some of this frigid air could spill into part of the northwestern U.S. this weekend.
This could result in disruptions to travel and commerce around the holiday, though ski resorts could have some success from consistent snow and cold conditions.
This active weather pattern is not expected to ease up too much next week, either, leading to post-holiday travel stress. AccuWeather forecasters will continue to monitor the upcoming storms and report with the latest updates.
For the latest weather news check back on AccuWeather.com. Watch the AccuWeather Network on DIRECTV, Frontier, Spectrum, fuboTV, Philo, and Verizon Fios. AccuWeather Now is now available on your preferred streaming platform.
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News / Winter Weather
Atmospheric river could snarl travel in the West as Christmas approaches
By Jessica Storm, AccuWeather Meteorologist
Published Dec 19, 2021 7:15 AM EDT | Updated Dec 21, 2021 6:21 AM EDT
An atmospheric river, or a plume of tropical moisture in the atmosphere, is expected to build into the western coast of the United States this week, bringing inordinate amounts of rain and snow to the drought-weary West and impacting travel as Christmas grows near.
Rain and snow have been slamming the Northwest this weekend, particularly around Portland and Pendleton, Oregon, where thick snowflakes were falling across portions of Clark, Multnomah and Clackamas counties on Saturday night and Sunday morning. Rain fell at Santiam Junction, as shown on highway cameras.
Flakes were sticking to cars and grass in Vancouver, Washington, but melted upon contact with roadways, while heavy snowfall was filmed in the Corbett area of Multnomah County, causing roads to become slick. Portland also recorded its first measurable snowfall of the season with 0.2 of an inch as of Sunday morning, before the city even fell below freezing.
Camp Bonneville, Washington, recorded 4 inches of snow as of early Sunday morning, with Camas, Washington, not too far behind with 2.8 inches of snow. By Sunday afternoon, a total of 18 inches of snow had fallen in Lucerne, Washington, with several other locations reporting above a foot.
Heavy rain caused the Marys River near Philomath, Oregon, to approach major flooding stage on Monday evening, which typically results in lowland and agricultural flooding, according to the NWS.
Earlier last week, the Southwest also had its fair share of precipitation as moisture moved onshore and brought over 3 inches of rain to San Francisco in one day on Dec. 13. Los Angeles International Airport reported over an inch of rain the following day, Dec. 14, while downtown received over 2 inches.
The storm track delivering this precipitation continued to target the northern half of the West on Sunday as most of the Southwest experienced dry conditions.
The opposite was true across the Northwest as valley rain and mountain snow continued to fall on Sunday. Rain continued in Portland and Eugene, Oregon, while snow fell late Sunday in Great Falls and Bozeman, Montana. From there, the focus of rain and snow began to vary each day and meander north and south.
Precipitation shifted northward on Monday and encompassed parts of northern Oregon and southern Washington.
Rain drenched parts of the Oregon and Washington coasts as snow (blue) fell over the interior and reached portions of northern Idaho and western Montana, on Monday, Dec. 20, 2021. (AccuWeather)
On Tuesday, the storm track is then forecast to shift southward, returning the focus of precipitation to the Southwest, but there can still be some lingering snow and rain in the coastal Northwest early in the week.
"The storm still spinning offshore will send another cold front toward the coast," AccuWeather Meteorologist Ryan Adamson said.
On Wednesday evening, a major storm is likely to begin across the West, producing rain and snow from Washington to Southern California.
"A sharp dip in the jet stream later this week will set the stage for a building atmospheric river into the West," said AccuWeather Senior Meteorologist Matt Rinde.
Cities in California like Redding, Sacramento, San Francisco, Fresno and Los Angeles can all experience 1-2 inches of rainfall from Wednesday afternoon through Saturday morning, with higher amounts in the mountains where temperatures are high enough for rain to fall.
"This pattern will lead to another round of heavy rain and mountain snow for the region," said Rinde.
AccuWeather Storm Warning Meteorologists are forecasting up to two feet of snow in the Cascades and 2-4 feet of snow across the Sierra Nevada from Tuesday evening to Saturday.
Such heavy precipitation could cause local flash flooding along with mudslides in burn scar areas, disrupting travel and producing extra traffic for shoppers. This could also delay last-minute packages before Christmas arrives. Motorists are urged to use caution and plan extra time to travel to their destinations.
CLICK HERE FOR THE FREE ACCUWEATHER APP
A winter storm watch has been issued for the Sierra Nevada Mountains through Sunday, warning commuters of difficult to impossible travel. Heavy snow can cause damage to trees and power lines across the area. By Monday evening, this had been upgraded to a winter storm warning in many areas in effect through the weekend.
"While this may be disruptive for holiday travelers, this is still a much-needed event for the region given the short-fall of rain for the last several years," Rinde said.
Nearly half of the West, which is comprised of Washington, Oregon, California, Nevada, Idaho, Montana, Utah, Arizona and New Mexico by the United States Drought Monitor, is in extreme drought. In fact, the only part of this region that is not at least abnormally dry is the far Northwest, where heavy rain flooded western Washington and northwestern Oregon earlier in the season.
Drought conditions are particularly bad across Central and Southern California, where over 80% of the state is in extreme drought and nearly a third in exceptional drought. Since the beginning of 2021, Los Angeles has only had 55% of its average precipitation, with Palmdale, California, at only a quarter of its yearly normal as the year approaches its end. Palm Springs, California, also makes the list with a third of its yearly average.
The storm may also drag enough cold air into the Northwest to drop snow levels below 1,000 feet in elevation, potentially bringing wintry weather to places like Seattle and Portland during the Christmas weekend, according to the long-range team.
"Air originating from Siberia will push southward across Alberta and southwestward across British Columbia Canada," AccuWeather Senior Meteorologist Brett Anderson said and added that some of this frigid air could spill into part of the northwestern U.S. this weekend.
This could result in disruptions to travel and commerce around the holiday, though ski resorts could have some success from consistent snow and cold conditions.
This active weather pattern is not expected to ease up too much next week, either, leading to post-holiday travel stress. AccuWeather forecasters will continue to monitor the upcoming storms and report with the latest updates.
In other news:
For the latest weather news check back on AccuWeather.com. Watch the AccuWeather Network on DIRECTV, Frontier, Spectrum, fuboTV, Philo, and Verizon Fios. AccuWeather Now is now available on your preferred streaming platform.
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