Winter has made an unusual return to the Northern Rockies as a late-June storm brings heavy snowfall to the mountains of Idaho and Montana, prompting expanded Winter Storm Warnings and hazardous travel conditions across several high-elevation passes.
The National Weather Service has upgraded the Lemhi, Bitterroot, Sapphire, Anaconda Pintler and Big Hole mountain ranges to Winter Storm Warnings, with more than a foot of snow forecast in the highest elevations through Monday. Forecasters say the most dangerous travel conditions will occur overnight into Monday morning.
Heavy Snow Expected Across High Elevations
The National Weather Service office in Missoula has kept Winter Storm Warnings in effect until 9 a.m. Monday for Western and Eastern Lemhi County, the Bitterroot and Sapphire ranges, and the Butte and Blackfoot region above 6,500 feet.
Snowfall totals of 4 to 8 inches are expected across much of the warning area, while the Anaconda Pintler Mountains near Georgetown Lake could receive between 8 and 16 inches. The highest peaks of the Lemhi Range may see up to 12 inches of snow. West winds of 10 to 20 mph, with gusts reaching 30 mph, are expected to produce blowing wet snow and reduced visibility.
Farther east, the National Weather Service office in Great Falls has issued a Winter Storm Warning through noon Monday for northwest Beaverhead County, including Chief Joseph Pass, Big Hole Pass, Wisdom, Wise River and Dewey. Snowfall of 2 to 6 inches is forecast at pass level, with more than 12 inches possible across the surrounding high terrain.
Mountain Passes Face Hazardous Travel
Several key mountain routes are expected to experience difficult driving conditions. The warnings include Idaho Highway 28 between Tendoy and Lone Pine, Lemhi Pass, Bannock Pass and US Highway 93 over Lost Trail Pass.
The Great Falls office also highlighted Interstate 90 at Homestake Pass in its Winter Weather Advisory, alongside US Highway 12 over Macdonald Pass and routes leading toward Yellowstone National Park. The advisory remains in effect until noon Monday and forecasts up to 5 inches of snow above 6,500 feet, with isolated amounts exceeding 9 inches on the highest peaks.
Forecasters warned that snow levels could briefly fall low enough to create slushy accumulations on Interstate 90 near Homestake Pass and on US 12 over Macdonald Pass, potentially impacting travel even at lower elevations.
Motorists are encouraged to check current road conditions before traveling through the mountains. Live updates are available through Montana 511.
Yellowstone Routes See Lighter Snowfall
Roads approaching Yellowstone National Park are expected to receive lighter snowfall than areas farther west. Targhee Pass on US Highway 20 and Monida Pass on Interstate 15 remain under a Winter Weather Advisory, with up to 4 inches of snow forecast and locally higher amounts on nearby peaks.
While late-season snow is not unheard of in the Northern Rockies, widespread Winter Storm Warnings at the end of June are unusual. The storm arrives as many summer travelers are using mountain highways with recreational vehicles, trailers and motorcycles, increasing the risk of weather-related travel disruptions.
