A winter storm threw about 20 inches of snow into northern Arizona on Sunday, with more expected today.

The National Weather Service has issued a Winter Storm Warning for the Kaibab Plateau, parts of the Mogollon Rim, Kokonino Plateau, the mountains of Yavapai County, the White Mountains, and northern Gila County through 11 pm Tuesday.

Snow rates can average up to 1 inch per hour.

With more snow expected, Northern Arizona University has already announced the cancellation of the first day of classes on Tuesday, as well as the Flagstaff Unified School District. Other local schools may follow suit.

The Arizona Department of Transportation warned Monday afternoon that winter weather would create dangerous travel conditions, with 35 mph wind gusts and snow-covered smooth roads.

Conditions are set to improve on Wednesday, with light snow showers likely to return on Thursday.

Real-time highway conditions are available on ADOT’s Arizona Traveler Information site at: az511.gov Or call 511.