Chance of ‘Major Impacts’ From Threatening Snowstorm Explained

Some parts of western Montana have a 50 percent chance of “major impacts” from an early-season snowstorm approaching the state this week.
National Weather Service (NWS) meteorologists issued a winter weather advisory for an area on Montana’s western side on late Wednesday morning. The advisory was issued by the Missoula office and will remain in place for western Lemhi County, eastern Lemhi County, Bitterroot/Sapphire Mountains and Butte/Blackfoot Region from 6 a.m. local time Thursday morning through 6 a.m. local time Friday morning.
There is a high chance for “moderate impacts” from the storm, the NWS office said, and a 50 percent chance for “isolated major impacts.”
“Wet snow expected above 6500 feet,” the advisory said. “Likelihood of moderate impacts from 3 to 6 inches of snow is greater than 90 percent, and up to a 50 percent chance of isolated major impacts from 6 to 10 inches or more of snow.”
NWS meteorologist Brian Conlan told Newsweek that snow this early in the fall season is not uncommon.
“About 10 days ago, we had snow levels down to high 5,000s, low 6,000s to the point where they had to close the Going to the Sun Road at Glacier National Park,” he said. “The late August stuff probably happens every two to three years, but at this point in time climatologically, snow levels can get down to 6,500 feet.”
Impacts of the impending storm could affect recreators, such as those hunting, hiking or camping. Conlan said they should prepare for wet, cold conditions on Thursday.
Areas most likely to experience impacts are Bannock Pass, Georgetown Lake, Lemhi Pass, Highway 28 from Tendoy to Lone Pine, Highway 93 from Sula to Lost Trail Pass, and Williams Creek Summit.
“For MODERATE to MAJOR impacts from snow, backcountry users should prepare for wet and raw conditions. Hazardous traveling conditions on backcountry roads is possible,” the advisory said. “Slow down and use caution while traveling. The latest road conditions for the state you are calling from can be obtained by calling 5 1 1.”
“Outdoor recreationalists should be prepared for winter conditions,” the advisory added. “Snowfall could impact roads and cold temperatures may result in hypothermia.”
The snow will likely melt by Saturday, Conlan said.
The storm is part of a weather system expected to impact the northern U.S. through the end of the week, an NWS forecast said. Parts of Idaho and northwest Wyoming also might be affected. In addition to snow at around 6,500 feet in elevation, the system also will bring “moderate to heavy rain and gusty winds” to parts of the Intermountain West and northern Rockies.
The storm will be driven by a deep upper low crossing from the Northwest on Wednesday before churning over the northern Rockies on Thursday. Most of the impactful precipitation will be confined to the northern Rockies and the High Plains in Montana. A few inches of rainfall could produce flooding throughout northwest Montana, prompting a “Slight Risk (level 2/4) of Excessive Rainfall both today and Thursday.”