White Christmas less likely for many, the Grinch to blame is climate change

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Snowplows are working Monday, January 28, 2013 to clear the streets of Salt Lake City following a snowstorm. New data analysis suggests some of us are less likely to have a White Christmas. (Scott G Winterton, Deseret News)

Estimated reading time: 4-5 minutes

NEW YORK – After all these years, Bing Crosby still fuels our dreams of a “White Christmas”. But new data analysis suggests some of us might be better off leaving that Christmas morning snow dream to holiday classics.

When meteorologists talk about “normal” or “average” weather, they are primarily referring to a set of data that takes into account conditions over the past three decades. This so-called normal data was updated this year and now includes more recent weather conditions – from 1991 to 2020 – which have tended to be milder and less snowy due to the climate crisis.

This week, scientists with the National Oceanic and Atmospheric Administration used that data to update the chances of at least an inch of snow on the ground on December 25.

So, cross your fingers and use the map below to see if there is at least a small chance to build Frosty on Christmas Day.

The greatest risk of snow on the ground on Christmas Day is roughly where you would expect; parts of North Dakota, Minnesota and Wisconsin have greater than 90% chance, as well as upstate New York and interior New England.

The cold, mountainous regions of the west also have a high risk of snowfall on December 25.

But what’s not clear about the map above is where those odds have changed. CNN has calculated the numbers for more than 2,000 locations that have already had a chance to have a White Christmas in normal NOAA data.

An astounding 64% of these places have a reduced likelihood of a White Christmas in the new normal data compared to the average for the past 30 years (which took into account weather conditions from 1981 to 2010).

This preliminary set of NOAA maps shows the maximum temperature change at the peak of each season between old climate normals (1981-2010) and new climate normals (1991-2020). (Photo: NOAA)

Only 31% of the stations increased their probability, leaving 4% of the locations remaining roughly the same.

“If you’re tempted to compare the two maps for signs of the influence of long-term warming, keep a few points in mind,” writes Rebecca Lindsey of NOAA. “From a normal 30-year period to the next, two decades of data are the same; only one in three decades is new. “

This means that the change from one normal to another can be relatively small since you are only changing one third of the data. “It also means that in some places the changes could be the result of natural decadal variability,” says Lindsey.

For example, take New York City in the first half of the 20th century, where you can see this decadal variability at work. Around 1940, when Irving Berlin wrote the song “White Christmas”, it had been a decade since there had been no Christmas snow in New York City, where he lived.

The city had an impressive run of White Christmases from 1911 to 1920 and then again in the late 1940s. After a lull, the 1960s produced another excellent decade for Christmas snow in Central Park.

Then the model switched to a much less frequent cadence. And there have only been four White Christmases in New York City since 1970. Since 2009, the town of “Miracle on 34th Street” has had no snow on the ground for Santa’s landing.

You can’t build a similar timeline for every location. In many places, weather data was extremely scarce prior to the 1980s. But the trend seen here in this new set of White Christmas probabilities echoes the changes scientists have seen in the United States.

“The spatial footprints of climate change that we expected from our modeling studies are visible in national patterns of change in temperature and precipitation normals,” Lindsey writes. “So it’s no surprise that there are subtle differences between the 1981-2020 version of the White Christmas Card and the 1991-2020 version that are consistent with the reality of long-term warming.”

Parts of the South, for example, had at least a small chance to see snow on Christmas Day. But that luck has faded in the latest data. It makes sense when you look at how the average December temperatures warmed up in the southeast.

The connection to how temperatures have changed is strong in the United States.

It may take another decade or two of record keeping to find out exactly how much the climate crisis is impacting your White Christmas dreams. But don’t go full Scrooge – there are always outliers.

“Although the map shows the historical probability that at least 1 inch of snow will be observed on December 25, actual conditions in any year can vary significantly from these as the weather conditions present will determine the snow on the ground or snowfall on Christmas Day, ”Lindsey adds optimistically. “These probabilities are only useful as a guide to show where snow on the ground is most likely.”

What if you always wonder – like the Haynes sisters in a “White Christmas” – “What is a Christmas without snow?” Take it from this writer who lives in the South and has just had his dreams shattered with the new probabilities: A Christmas without snow is Christmas again!

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