New 'normal' reshaping white Christmas chances across U.S.

From Home Alone to It's a Wonderful Life, nearly every Christmas movie features a snow-covered landscape. But how realistic is it to wake up on Dec. 25 to a snowy scene? The odds are changing.

On Friday, NOAA released an update to its white Christmas climatology, or the chance for an inch of snow to be on the ground any given year on Dec. 25. This could be new snow falling on Christmas Day or snow still covering the ground from a recent storm.

Experts analyzed data from nearly 15,000 weather stations across the contiguous United States to show the likelihood of white Christmas dreams becoming a reality.

Meteorologists typically use 30-year averages for a snapshot of the recent climate for an area, including when snow usually falls. Previously, this meant using weather data from 1981 through 2010, but with the recent turning of the decade, the averages shifted to include observations from 1991 and 2020.

"The 1991-2020 Climate Normals are the latest three-decade averages of several climatological measurements," NOAA said in its press release.

Earlier this year, NOAA released new normals across the U.S. based on the shift in the years, but with the arrival of the holiday season, the agency released an updated look at average snowfall probabilities in late December specifically with Christmas in mind.

The odds of experiencing a white Christmas did not change for some areas, such as the coast of California and the Gulf Coast states, where there is almost no chance for snow on the ground on Dec. 25. Similarly, a white Christmas remained a certainty across the intermountain West, mountains of New England and parts of the Upper Midwest.

According to experts at NOAA, the chances for a white Christmas dropped as much as 10 across the central Plains, Midwest and parts of the Northeast. This includes Chicago, St. Louis, Detroit and Indianapolis but doesn't completely rule out the opportunity for fresh powder falling in time for the holidays.

Other regions of the country experienced more frequent snow on Christmas, including the Great Basin, the northern Plains and part of the Rocky Mountains.

According to the new 30-year averages, the possibility of experiencing a white Christmas in Denver dropped by 6.3 points, one of the highest drops of all of the major cities across the U.S.

The chances for snow on the ground on Dec. 25 in any given year also fell slightly in Boston, Philadelphia and Washington, D.C., while increasing slightly in New York City.

This map shows the updated white Christmas probabilities based on the 1991-2020 climate normals.

"While the map shows the historical probability that a snow depth of at least 1 inch will be observed on Dec. 25, the actual conditions in any year may vary widely from these because the weather patterns present will determine the snow on the ground or snowfall on Christmas Day," NOAA explained.

NOAA added that climate change is not behind every revision of the white Christmas climatology, but it did have an influence.

"It's not surprising that there are some subtle differences between the 1981-2010 version of the white Christmas map and the 1991-2020 version that are consistent with the reality of long-term warming. "