Forecasters are predicting a big change in the weather across Montana this week with much colder temperatures and snow.

According to the National Weather Service office in Missoula, a much colder airmass from northwest Canada will spread south and enter northcentral Montana Tuesday before expanding across the remainder of the state Tuesday night through Wednesday.

While snowfall totals aren’t expected to be substantial locally, Libby, Troy and Eureka area residents can expect overnight lows in the teens and daytime highs ranging from the mid 30s to mid 40s for the rest of the week.

Tuesday night and Wednesday may see snow accumulation of about one inch. Tuesday, the snow level is predicted to drop to 2,800 feet.

Conditions will include patchy fog first thing in the morning on Wednesday night and Thursday as well as partly sunny conditions from Thursday through Sunday.

Out at Happy’s Inn, the chance of accumulating snow is similar while temperatures are predicted to be colder on average.

In the Marion area, temperatures will also be colder and one to two inches of snow is possible.

West Glacier has a winter storm watch for Tuesday and Wednesday with three to eight inches of snow in the forecast.

On the Continental Divide, a winter storm watch is in effect for Tuesday and Wednesday with the possibility of four to 10 inches in the East Glacier Park region.

Officials say travel could be very difficult to impossible and tire chains may be required for some vehicles. Those in the backcountry should ensure they have appropriate knowledge and gear and may want to consider alternate plans. The hazardous conditions could impact the Tuesday evening and Wednesday morning commutes.

In other Western Montana locales, varying degrees of snow accumulation are predicted.

Heavy snow is possible with total snow accumulations between three and 12 inches possible in Homestake Pass, Highway 12 Garrison to Elliston, MacDonald Pass, Butte, Georgetown Lake, Highway 83 Seeley Lake to Condon, Interstate 90 East Missoula to Bearmouth, and Highway 200 Bonner to Greenough.

In central Montana, including Great Falls, a winter storm watch is in effect Tuesday and Wednesday with five to eight inches at lower elevations and eight to 15 inches in the mountains.

Helena may see three to seven inches of snow.

To the West, the Weather Service says winter storm could have impacts on roads through mountain passes in Washington, including Stevens, Blewett, Loup Loup, Sherman and Lookout.