FLAGSTAFF, Ariz.—The unseasonably warm weather in Arizona came to an end this week as a storm system approached carrying rain and snow.

The storm will hit western Arizona on Thursday afternoon and spread eastward through Friday morning, dropping up to 10 inches of snow in cities along the Mogollon Rim and three-quarters of an inch of rain in southwestern and central Arizona. More snowfall is expected in mountainous areas around the state.

The National Weather Service said Interstate 17 south of Flagstaff and parts of Interstate 40 will be slick and snow-covered, and back country roads might become impassable. The storm also will dump heavy snow in parts of New Mexico, adding to what was the state's first significant winter storm earlier this week.

Northern Arizona University has pushed back its Friday morning commencement ceremony and combined two scheduled for later in the day because of the storm. The university urged students who don't plan to participate or attend graduation to leave campus as early as possible Thursday to avoid bad weather and cut down on traffic across campus Friday.

Flagstaff, which typically would have nearly 18 inches of snow by now from the winter season that starts in September, has had only 1.1 inches so far, said Chris Outler, a meteorologist with the National Weather Service in Flagstaff. The temperatures in the mountain city have been about 7 degrees above normal, but the average will come down with Thursday's storm.

The snow that is on the way "is kind of what we come to expect this time of year, but it's just been so long since we've had anything," Outler said.

The average snowfall in December is 17.9 inches.

Window Rock on the Navajo Nation is expected to get up to 6 inches of snow in the upcoming storm, and forecasters are calling for up to 8 inches in Show Low. Winslow and Holbrook along Interstate 40 largely will be sheltered from snow, as well as other elevations below 5,000 feet, Outler said.

Rain is a certainty for Tucson, Phoenix and outlying areas Thursday night, with lingering showers on Friday, forecasters said.

The National Weather Service in Albuquerque, N.M., said the mountains of northern and central New Mexico will be likely to see significant snow.

Several inches of snow will fall in lower elevations along and west of the Continental Divide. Officials say travelers should be especially careful on Interstate 40 between Grants and Gallup on Friday.