(CNN) — Those heading home from Christmas destinations could face travel woes, particularly around the Rockies and upper Midwest.

Blizzard conditions are sweeping through Arizona, Colorado, New Mexico, and extending up into the Dakotas, bringing potentially dangerous black ice to roadways.

By Sunday morning, more than eight inches of snow blanketed parts of northern Utah and southeastern Idaho.

But for most, the weather outside isn't so frightful -- especially if you're in the central and eastern United States.

It's a mild Christmas, with warmer than usual temperatures for December, particularly in the Southeast: Atlanta is forecast to reach a high near 70 on Christmas Day, while a balmy 80 is expected in Orlando.

Forecast highs for Sunday are 5 to 15 degrees above average from the Plains to the East Coast, according to the National Weather Service.

With such mellow weather, airports weren't the nightmare that many have come to dread during the holiday season.

The United States had about 100 flight delays by Sunday morning, and 1,000 on Saturday, according to the FlightAware flight tracking website

Snow on the Western front

A major winter storm that brought heavy rain along the West Coast and widespread, heavy snow in the Rockies moved east, producing blizzard conditions and bringing a whiteout Christmas across parts of the Northern Plains.

The National Weather Service in Bismarck warned that traveling would be "dangerous if not impossible" on Christmas and into Monday.

26.8 million people were under some form of a winter weather advisory, watch, or warning across the United States.

Blizzard watches remain in effect in the Northern Tier through Monday morning.

Unseasonable warmth

CNN

Warm air is being pushing into the Midwest and Northeastern United States, bringing an unusually mild Christmas to cities that typically get snow this time of year.

Instead of a white Christmas, a swath of rain will expand from the Great Lakes, bringing a wet Christmas to New York, Boston and Massachusetts.

Atlanta set a record high temperature for Christmas Eve at 73 -- one degree higher than the previous record set in 2015.