HELENA, Mont. (AP) — The first major snowstorm of the season is expected to hit the northern Cascades and Rockies and move into North Dakota this week, sending residents searching for their winter coats, gloves and boots and facing much different driving conditions after a warm fall in many places.

The National Weather Service is warning of hazardous travel on snowy mountain passes and ice on some highways when snow initially melts and then freezes as road temperatures drop.

The storm is forecast to begin Tuesday with rain at lower elevations in Washington and snow in the mountains before spreading snow across northern Idaho, Montana, northwestern Wyoming and North Dakota.

Cold air moving down from northwestern Canada will combine with a moist Pacific weather system leading to freezing temperatures and snowfall amounts up to 18 inches (46 centimeters) in the mountains of Montana, the National Weather Service forecasts. Some higher elevations in the northern Rockies could see snow totals of 2 feet (61 centimeters) or more.

Central Montana will see the worst of the snow, said Matt Ludwig, a meteorologist with the National Weather Service in Great Falls.

“We kind of are the bull’s-eye,” he said.

The first snowfall of the season “is always the most dangerous because people just aren’t used to it yet” after driving for months on mostly dry pavement, Ludwig said. Drivers aren’t used to dealing with less traction, slower speeds and longer stopping distances, he said.

The forecasted snow prompted residents to make appointments to get their snow tires put on and caused some to realize their underground sprinkler systems needed service.

Things started picking up at Eagle Tire in Helena, Montana, where crews swapped out regular tires for snow tires on 30 vehicles on Monday, manager Payton Lester said. He said they had about 40 more appointments to do the same Tuesday.

At Spieker Sprinklers in Helena, the winterization program is full and they had to turn away callers Tuesday, owner Joe Spieker said.

The storm brings a sharp change in weather. Helena tied record temperatures in the lower 80s late last week, which is about 25 degrees above average for this time of year, Ludwig said. Great Falls also had a day in the low 80s late last week, and now those cities could see 8 inches (20 centimeters) of snow by Wednesday.

“If that’s not a shock to your system, I don’t know what is,” Ludwig said.