A winter storm in Montana and Wyoming has prompted forecasters to issue a warning that people could become stranded in the mountains if they travel in bad weather.

National Weather Service (NWS) meteorologists in the Billings, Montana office issued the winter storm warning early Tuesday morning. The warning is in effect for the Pryor Mountains and northern Bighorn Mountains in Montana and the northeastern Bighorn Mountains in Wyoming until noon Wednesday local time.

The warning urged people to postpone travel if possible as up to 20 inches of snow was expected. Bad weather would likely make traveling along Highway 14 “very difficult.”

“The hazardous conditions will impact backcountry recreation through Wednesday morning,” the warning said.

Conditions were expected to be so extreme that forecasters suggested people stock their cars with survival supplies in case they became stranded in the mountains.

“People should think about postponing all travel. If the trip is absolutely necessary, drive with extreme caution. “Consider bringing a winter storm kit that includes things like tire chains, jumper cables, flashlight, shovel, blankets and extra clothing,” the warning said. “Also, take water, a first aid kit and anything else that will help you survive in the event of a stranding.”

NWS meteorologist Luke Arends recounted Newsweek that you should always travel with winter survival gear. He said the snow was related to a typical fall system for the region.

“It's what we call a trough that's moving inland from the Pacific Northwest and moving through our area,” Arends said.

Arends said the heaviest snow will fall on the higher peaks of the Bighorn Mountains on the northern slopes. Lower amounts of up to 12 inches are forecast for the Pryor Mountains. Some foothills could also see some snow, and Arends said although temperatures are still too warm for snow in Sheridan County, Wyoming, it could start to snow in that area as temperatures rise later in the day sink.

Rain will fall in areas where temperatures do not fall below freezing.

The best chance of snow will be Tuesday afternoon. Snowfall will ease overnight and into Wednesday morning.

Another system will move into the area later this week, but Arends said it likely won't produce any more snow. Temperatures will remain close to the seasonal average for the rest of the week.

Winter storm warnings were also issued in South Dakota and Wyoming. Winter weather advisories were more widespread, extending into Utah and Colorado and were accompanied by freeze warnings and warnings.