Pittsburgh region won't see a white Christmas, like most years

If you are pining for that nostalgic white Christmas depicted on holiday greeting cards with billowing swirls of clean snow, don’t look to the Pittsburgh region this weekend.

Christmas Day will be unseasonably warm, with a potential high of 57 degrees and a low of 42, said David Shallenberger, lead meteorologist with the National Weather Service office in Moon Township.

But that shouldn’t be surprising.

The Pittsburgh region sees an official white Christmas about 30% of the time, according to an analysis of NWS data for the last 70 years.

By comparison, the ridges of Laurel Summit in Westmoreland County have about a 66% chance of snow, on average, according to the National Oceanic and Atmospheric Administration (NOAA).

Since 1871, the Pittsburgh region has had at least a tenth of an inch of snow on the ground on 56 Christmas Days, records show.

Officially, though, at least an inch is required — not counting snowfall during the day — to be considered a white Christmas, per the NWS. There have been 22 of those since 1948, when local NWS records are available for daily snow totals.

Small decline nationally

Less of the country has snow for Christmas than in the 1980s, an Associated Press analysis of U.S. snow measurements found. That’s especially true in a belt across the nation’s midsection — from Baltimore to Denver and a few hundred miles farther north.

What snow that does fall doesn’t measure up to past depths, according to the AP analysis.

Nationally, scientists say the decline in the number of white Christmases is relatively small and caution about drawing conclusions.

The average December temperature in the continental U.S. was a tad below freezing from 1981 to 1990, federal weather records show. And from 2011 to 2020, it was up to an average slightly above 35 degrees, considerably above the freezing mark.

From 1981-90, on average, almost 47% of the country had snow on the ground Christmas Day, with an average depth of 3.5 inches, according to an analysis the University of Arizona completed for The Associated Press. From 2011-20, Christmas snow cover was down to 38%, with an average depth of 2.7 inches.

In 20 to 30 years “with climate warming, the prospects of a white Christmas in many parts of the U.S.A. will be slim indeed,” said Mark Serreze, director of the National Snow and Ice Data Center in Boulder, Colo.

A data set from Rutgers University’s global snow lab finds continental U.S. snow in the last week of December slightly increasing, not decreasing, said climate scientist David Robinson, whose data based on satellite imagery goes back to 1966.

“There’s no trend. You just don’t see it,” Robinson said.

Often people in their 60s and 70s think there are fewer white Christmases, he added, because the 1960s had more than usual white Christmases.

Bigger than one day

That certainly was the case in the Pittsburgh region.

The decade of the 1960s here saw snow on the ground in all but one year, NWS data shows. That included six official white Christmases.

Snowfall on Dec. 25 in Southwestern Pennsylvani actually has increased slightly, by a tenth of an inch, while snow depth has decreased by two-tenths of an inch in the last 70 years, according to Shallenberger.

“Looking at the data for one day doesn’t tell us that much about what is generally happening to our snow and temperatures during a season for a month,” he said.

If measuring just Christmas temperatures, there is not much of a change over the last 70 years, Shallenberger said. However, looking at the month of December since 1950, highs for December have dropped about 2 degrees, he said.

Although the service has kept records since 1871, the earliest readings were taken at previous locations, including Pittsburgh, which is notably warmer than Moon Township, Shallenberger said.

“You still have variability in your temperatures and the amount of snow, but the temperatures are getting warmer with less snow over time,” he said.

Whether it’s snowy or warm, the weather can be highly variable on Christmas day, no matter the long-term trends.

Although warm temperatures are expected Saturday, two dozen Christmas Days over the past 150 years that have been 50 degrees or warmer, according to NWS data. The record is 67 degrees – set in 1895.

“I don’t think anyone can deny we are looking at a warming trend, but pegging it to one day doesn’t say enough for the season.”