UPDATE, Sunday, June 28, 11:50 AM MT: The heavy snow zones, the Lemhi, Bitterroot, Sapphire, Anaconda Pintler and Big Hole ranges, hold their winter storm warnings through Monday. The Great Falls office now names Homestake Pass on Interstate 90 directly in its winter weather advisory, in the Elkhorn and Boulder Mountains zone, alongside Macdonald Pass on US 12 and the Yellowstone gateway passes. That advisory runs until noon Monday and calls for up to 5 inches of snow above 6,500 feet, with localized amounts over 9 inches near the highest peaks. Check Montana 511 for live pass conditions.
More than a foot of snow is now forecast across parts of Idaho and western Montana, with two National Weather Service offices upgrading the Lemhi, Bitterroot, Anaconda Pintler and Big Hole high country to Winter Storm Warnings. The storm could also leave slush on lower-elevation highways, including Interstate 90 near Homestake Pass.
Peak Driving Danger WindowNow through 9 AM Monday in Idaho and the western Montana ranges, and through noon Monday in the Big Hole country, with snow heaviest overnight and early in the morning.
Winter Storm Warnings Expand Across Idaho and Montana
The late-June storm forecasters warned about has moved over the Northern Rockies, and the snow is piling up on the high passes of Idaho and Montana. Just days after temperatures reached the 80s and low 90s in the valleys, winter has returned to the highest elevations. By Sunday morning, Winter Storm Warnings covered parts of Idaho and western Montana, with more than a foot of snow forecast on the tallest peaks through Monday.
The Missoula office kept its winter storm warning in force for Western and Eastern Lemhi County, the Bitterroot and Sapphire ranges, and the Butte and Blackfoot region above 6,500 feet, running until 9 AM Monday. Totals of 4 to 8 inches are expected, with 8 to 16 inches across the Anaconda Pintler Mountains near Georgetown Lake and up to 12 inches on the highest Lemhi peaks. Forecasters added that west winds of 10 to 20 mph, gusting to 30, will drive the wet snow and deepen the chill.
Farther east, the Great Falls office raised Northwest Beaverhead County to a winter storm warning of its own, in effect until noon Monday. That zone, which takes in Chief Joseph Pass, Big Hole Pass, Wisdom, Wise River and Dewey, can expect 2 to 6 inches at pass level and more than a foot in the higher terrain.
Where The Warning Hits The RoadZone
Alert
Snow
Key routes
Anaconda Pintler / Butte and Blackfoot (MT)
Winter Storm Warning
4 to 8 inches, 8 to 16 on Anaconda Pintler
Georgetown Lake area
Western and Eastern Lemhi County (ID)
Winter Storm Warning
4 to 8 inches, up to 12 on peaks
Highway 28 Tendoy to Lone Pine, Lemhi Pass, Bannock Pass
Bitterroot and Sapphire Mountains (MT)
Winter Storm Warning
4 to 8 inches
US 93 over Lost Trail Pass
Northwest Beaverhead County (MT)
Winter Storm Warning
2 to 6 inches at pass level, over a foot up high
Chief Joseph Pass, Big Hole Pass
Yellowstone gateway zones (MT)
Winter Weather Advisory
Up to 4 inches, localized over 8 on peaks
US 20 Targhee Pass, I-15 Monida Pass
For drivers, the storm reaches several named routes. The warning covers Idaho Highway 28 between Tendoy and Lone Pine, Lemhi Pass and Bannock Pass, and US 93 over Lost Trail Pass in the Bitterroot zone. Lemhi Pass, an unpaved Continental Divide crossing at 7,373 feet, is among the first to turn to mud and snow. Lower down, the Missoula office said snow levels could briefly drop far enough to leave minor slushy accumulation on Interstate 90 at Homestake Pass and on US 12 over Macdonald Pass, both near Butte and Helena. The office advised that "persons should consider delaying travel across the backcountry and higher elevations."
Roads approaching Yellowstone National Park are expected to see lighter snowfall than the Bitterroot and Lemhi regions. Targhee Pass on US 20 and Monida Pass on Interstate 15 remain under a Winter Weather Advisory, with up to 4 inches of snow expected and locally higher totals on the surrounding peaks.
Late-June winter storm warnings are uncommon across the Northern Rockies, arriving at a time when many travellers are towing campers, motorcycles are out in force, and few drivers expect winter conditions.
What Drivers Should Do- Check Idaho 511 and Montana 511 for live pass conditions before you leave.
- Carry chains or traction devices if you plan to cross any of these passes.
- Pack a winter kit even in summer: blanket, water, flashlight, shovel and warm layers.
- Slow down on bridges and shaded curves, where wet snow freezes first.
- Build in extra time, and be ready to turn back if a pass closes.
Low valleys, including Salmon and the towns along US 93, are seeing rain rather than snow. The heavy snow is a high-country story, focused on the passes and peaks, and totals can still shift through Monday. Anyone crossing these routes should check the road first.
Conditions are expected to change quickly through Monday as snow levels fluctuate. Anyone planning to cross the higher passes should check Idaho 511 or Montana 511 before setting out, as additional warnings or changing road conditions remain possible.