Northern Rockies Face Early Snowstorm as Temperatures Plunge

A major shift in western US weather will bring the season's first widespread snowfall to the Northern Rockies from Saturday, Oct. 10, through Monday, Oct. 12, as a powerful cold front drives temperatures sharply lower. Forecasters expect heavy mountain snow, gusty winds and rain, with moisture from the remnants of eastern Pacific Hurricane Rachel contributing to the unusual early-season system.

The National Oceanic and Atmospheric Administration's Weather Prediction Center expects accumulating snow across the region, while AccuWeather forecasts up to 6-12 inches at elevations as low as 4,000 feet. The highest terrain could receive about a foot, and some mountain passes may experience travel disruptions.

The Weather Prediction Center described the approaching event in its Oct. 7 update: "The first widespread snowfall of the season is expected across the Northern Rockies this weekend into early next week," the agency said.

AccuWeather senior meteorologist Brett Anderson outlined the expected snowfall amounts and timing in his forecast.

"This will be a significant early-season snowfall for 6-12 inches of snow at elevations as low as 4,000 feet in the northern part of the Rockies from Saturday [Oct. 10] through Monday [Oct. 12]," said Brett Anderson, senior meteorologist at AccuWeather.

AccuWeather senior meteorologist Adam Douty said snow levels would fall below those seen during recent high-elevation snowfall in the Cascades and northern Rockies.

"While there has been some high-elevation snow in recent weeks in the Cascades and northern Rockies, snow levels will dip much lower in portions of Idaho, Montana and Wyoming," said Adam Douty, senior meteorologist at AccuWeather.

Douty also noted that some valleys could experience their first snowfall of the season while higher elevations receive heavier accumulations.

"Snow will fall for the first time in some of the valley locations in this region, with heavy snow over the higher terrain," said Adam Douty, senior meteorologist at AccuWeather.

The Weather Prediction Center said moisture associated with Rachel's remnants would interact with a broad low-pressure trough, bringing heavy rainfall and localized flash flooding from the Southwest and Great Basin into the Rockies and northern Plains on Sunday, Oct. 11, and Monday, Oct. 12.

"Furthermore, cold air surging behind the cold front will lower snow levels, leading to accumulating snow over high elevations across the northern Rockies through Monday [Oct. 12] causing possible minor to moderate impacts," the Weather Prediction Center said.

The National Weather Service office in Missoula, Montana, highlighted the unusual arrival of tropical-system moisture in the region.

"This is a very rare circumstance, but moisture from the remnants of Hurricane Rachel will track northeastwards from California and Nevada towards the Yellowstone and Wyoming area," the National Weather Service in Missoula said.

Western Montana will also face strong winds ahead of the cold front on Friday. National Weather Service meteorologist Trent Smith warned that the combination of gusty winds and dry conditions could push many areas, particularly southwestern Montana, toward critical wildfire conditions.

Smith characterized the approaching system as "a taste of winter."

He described the expected conditions across the region.

"That’s going to be bringing a lot of moisture, a lot of cold air and a lot of wind to the region," said Trent Smith, meteorologist with the National Weather Service.

Smith said the combination of cold air and precipitation could produce substantial accumulations along the Continental Divide and affect mountain-pass travel.

"We are looking at the potential of about maybe up to a foot of snow in the higher terrain along the Continental Divide, and maybe a couple of inches on the mountain passes which could have a pretty good impact," said Trent Smith, meteorologist with the National Weather Service.

In western Montana, valleys east of Highway 93 could receive 1-3 inches of slushy snow from Saturday night into Sunday. The Missoula and Bitterroot valleys may see scattered rain and snowflakes, although forecasters do not expect accumulation there.

Visitors to Glacier National Park should prepare for heavy snow, according to AccuWeather. Yellowstone National Park could also see accumulating snow at intermediate and high elevations.

The Weather Prediction Center said the approaching system would also mark a broader change after several weeks of unusual warmth across the West.

"A long-duration October heatwave across portions of California and the Desert Southwest is showing signs of easing as a major shift in the upper-air pattern is in store for the western U.S.," the Weather Prediction Center said.

AccuWeather senior meteorologist Alex Sosnowski attributed the developing storm to a significant change in the jet stream's position.

"A major pattern change is coming to the western United States this weekend, as the jet stream takes a plunge, helping to fuel a substantial early-season snowstorm for parts of the Rockies," said Alex Sosnowski, senior meteorologist at AccuWeather.

Forecasters also warned that the snow's consistency could create infrastructure problems, particularly where trees and power lines remain vulnerable to additional weight.

"The snow is expected to be heavy and wet with this event, which may weigh down power lines and trees," the Weather Prediction Center said.

Temperatures in western Montana are forecast to run 15-20 degrees below seasonal averages during the weekend. According to the Montana Public Radio report, temperatures should rebound into the 50s and 60s next week, although highs in the upper 70s are expected to become less common.