BUTTE, Mont. — Montana’s first significant winter storm of the season is moving into the state this weekend, with the National Weather Service warning that portions of Interstate 90 could see heavy snow, blowing snow, slushy pavement and rapidly deteriorating travel conditions from Saturday evening through Monday morning.
The storm is expected to hit some of the most important mountain sections of I-90, including Homestake Pass, Bozeman Pass, the Butte corridor, and stretches east of Missoula toward Bearmouth and eastward from Big Timber toward Livingston.
Winter Storm Warnings are in effect from 6 p.m. Saturday through 6 a.m. Monday for Homestake Pass and Bozeman Pass, where forecasters expect some of the most significant travel impacts.
The National Weather Service in Great Falls is forecasting 6 to 14 inches of snow in the Elkhorn and Boulder Mountains, including Homestake Pass, with wind gusts up to 40 mph. Bozeman Pass and the Big Belt, Bridger and Castle Mountains are under a separate warning calling for 6 to 13 inches of snow with gusts as high as 40 mph.
Forecasters warned that travel could become “very difficult” in those areas.
Farther east, a Winter Weather Advisory covers the I-90 corridor from Big Timber to Livingston and over Bozeman Pass, where 2 to 6 inches of wet snow and blowing snow are expected. Winds may also gust to 40 mph, creating reduced visibility and areas of slushy or snow-covered pavement.
Western Montana will also see impacts.
The National Weather Service in Missoula has placed I-90 from East Missoula to Bearmouth under a Winter Weather Advisory from Saturday evening through Monday morning, with 2 to 6 inches of snow possible and winds gusting to 40 mph.
Warm pavement may delay accumulation — then conditions could change quickly
One of the unusual features of this storm is the sharp transition from recent warm weather to winter conditions.
The National Weather Service in Missoula said road temperatures remain relatively warm after several mild days, meaning much of the initial snow may melt when it first reaches paved surfaces.
That could create deceptive conditions early in the storm.
Forecasters expect roads to begin wet before becoming slushy as temperatures fall and snowfall rates increase.
At mountain passes, the National Weather Service says snow may eventually accumulate on top of that slushy base, creating exactly the kind of changing traction conditions that can become dangerous for heavy commercial vehicles.
The agency said snow levels will drop enough by Saturday evening for snow to reach many valleys across west-central, northwest and southwest Montana.
Homestake, Rogers and MacDonald passes could each receive more than four to six inches by Monday morning, according to the Missoula forecast discussion.
I-90 truck traffic faces multiple trouble spots
For professional drivers, the storm’s timing and geography are particularly important.
Interstate 90 crosses several major mountain passes through Montana and carries significant east-west commercial freight traffic between Idaho, Montana, Wyoming, the Dakotas and points farther east.
The I-90 sections most likely to see winter-driving problems include:
East Missoula to Bearmouth — 2 to 6 inches possible under a Winter Weather Advisory.
Garrison and the Butte area — snow spreading into the corridor Saturday afternoon and evening, with nearby higher terrain under stronger warnings.
Homestake Pass east of Butte — 6 to 14 inches possible with 40 mph wind gusts under a Winter Storm Warning.
Bozeman Pass — 6 to 13 inches possible in the surrounding mountains with 40 mph gusts, while the broader I-90 corridor toward Livingston could see slushy roads, blowing snow and reduced visibility.
Big Timber to Livingston — 2 to 6 inches of wet snow and blowing snow, with the National Weather Service specifically warning of difficult travel on I-90.
For empty or lightly loaded trailers, gusty winds may create an additional stability concern, especially in exposed areas and while crossing mountain passes.
Wet, heavy snow could also bring down branches and power lines
This is not expected to be a dry, powdery winter storm.
The National Weather Service repeatedly describes the expected snow as wet and heavy, particularly across the higher terrain.
That matters because wet snow combined with 35- to 45-mph wind gusts can weigh down trees and power lines.
Forecasters say isolated power outages are possible across parts of central and southwest Montana.
Heavy wet snow can also complicate truck travel by building up on equipment, reducing visibility and creating slush before roads become fully snow covered.
Highest totals could approach 20 inches away from I-90
The most extreme snowfall totals are forecast north and west of the main I-90 corridor.
Areas around the Southern Rocky Mountain Front, MacDonald Pass and portions of central Montana could receive 10 to 20 inches of snow, with gusts as high as 45 mph.
The Absaroka, Beartooth and Crazy mountains could receive 10 to 18 inches in the highest terrain.
Those higher totals illustrate the strength of the system even though lower-elevation highways may initially see more rain, wet pavement and slush before accumulating snow develops.
Truckers should expect conditions to worsen after dark
The timing could be especially important for overnight commercial traffic.
The strongest winter conditions across many I-90 passes are expected after sunset Saturday and through Sunday night, when pavement temperatures fall and snow begins sticking more efficiently.
The National Weather Service said accumulation on paved surfaces will be most likely from the evening through late morning hours.
That means drivers who encounter only wet pavement Saturday afternoon could face dramatically different conditions several hours later.
A road that is simply wet entering a pass may be snow covered or slushy by the time a driver reaches the summit or begins descending the other side.
For tractor-trailers, that transition can affect braking distance, traction and downhill speed control.
Drivers should also be prepared for changing visibility where blowing snow develops.
MDT cameras and 511 will be critical through the weekend
The Montana Department of Transportation maintains live highway cameras across the state, including at Garrison, Homestake Pass and Bozeman Pass, allowing drivers to check actual roadway conditions before committing to mountain routes.
The National Weather Service is urging motorists who must travel to carry extra food, water and a flashlight and to check Montana’s 511 system for the latest highway conditions.
At the time of the latest Saturday morning observations, winter conditions had not yet fully developed across several I-90 locations, but warnings remain in place as colder air moves into the state.
The first real winter test of the season
The rapid change in Montana’s weather is notable.
Just days ago, parts of the state were dealing with unusually warm temperatures and fire-weather concerns.
Now, the National Weather Service is describing the incoming system as the first winter storm of the season, with heavy snow, strong winds and hard freezes expected across parts of the state.
For the trucking industry, that means winter-driving conditions are arriving quickly and well before many drivers may have fully transitioned into winter operating habits.
The biggest concern along Interstate 90 will be the combination of wet pavement, falling temperatures, heavy snow and wind across the mountain passes.
For drivers crossing Montana this weekend, the safest approach will be to treat the storm as a full winter event, not an early-season nuisance.
Conditions could deteriorate quickly from Saturday evening through Monday morning, particularly at Homestake Pass, Bozeman Pass and other elevated sections of the I-90 corridor.
