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How the odds of a white Christmas have changed
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How the odds of a white Christmas have changed


Meteorologists refer to “normal” and “average” weather in general when they talk about the data set that includes conditions over the past three decades. This so-called “average” weather refers to a data set that takes into account conditions over the past three decades. normals data was updated this year, and now includes more recent weather — from 1991 to 2020 — which has tended to be milder and less snowy due to the climate crisis.

You can cross your fingers and use this map to see if Frosty still has a chance of being built on Christmas Day.

The ground has the highest snow chance Christmas Day is pretty typical. There are parts of North Dakota, Minnesota, and Wisconsin that have chances greater than 90%. Upstate New York and the interior of New England also have chances.

Also, snow is possible in the West’s mountainous regions on December 25.

The map above doesn’t show where these probabilities have changed. CNN analyzed the data for more than 2000 locations that have ever experienced a white Christmas according to NOAA’s normals data.

A remarkable 64% of these locations have a lower chance of having a white Christmas, according to the new normals data. This is compared to the 30-year average which took into account weather conditions from 1981 to 2010.

Only 31% increased the probability of stations, while 4% of locations remained the same.

“If you find yourself tempted by the temptation to compare the two maps looking for signs of long-term heating, there are a few things you should keep in mind,” Rebecca Lindsey, NOAA. “From one 30 year normals period to another, two decades worth of data are the same; only a decade out of three of them is new.”

This means that the difference between one normal and another can be very small as you only have to change a third. Lindsey explains that some changes could be caused by natural decadal variability.

Take New York City in its first half of 20th century. Here you can see the decadal variability at work. Irving Berlin’s song “White Christmas” was written in 1940. It had been a decade that there had been snow in New York City.

From 1911 to 1920, the city experienced a string of white Christmases. This continued until the end of the 1940s. After a brief lull, the 1960s saw another decade of snow in Central Park.

The pattern has changed to a less frequent cadence. Since 1970, New York City has seen only four white Christmases. Since 2009, Santa’s landing has been impossible in the city of Miracle on 34th Street.

You can’t create a similar timeline for each location. Many places have very little weather data prior to the 1980s. The trend shown in this new set white Christmas probabilities mirrors the changes scientists have observed across the US.

“The spatial fingerprints that climate change would be expected based on our modeling studies can be seen in national patterns of change in temperature and precipitation NormalsLindsey wrote. “So, it’s not surprising there are subtle differences between the 1981-2020 and 1991-2020 versions of the white Christmas map that are consistent with long-term warming.”
Parts of the South had at most a slight chance of getting snow on Christmas Day. The latest data shows that this chance has decreased. It makes sense when you consider how average December temperaturesAcross the Southeast, it has warmed.

All across the US, there is strong evidence of a connection between how temperatures have changed and how they have changed. The Northern Plains showed the lowest average temperature in the new normals data. However, white Christmas chances increased in that region.

This preliminary set of maps from NOAA show the change in maximum temperature in the peak of each season between the old climate normals (1981-2010) and the new climate normals (1991-2020).

It could take another decade of record-keeping before we can see how the climate crisis is affecting white Christmas dreams. But don’t go full Scrooge — there are always outliers.

Lindsey optimistically says that the map shows the historical probability for at least 1 in snow to be observed on December 25. However, the actual conditions in any given year will vary because of the weather patterns. “These probabilities can only be used as a guide to show where snowfall is more likely.

And if you are still wondering — like the Haynes sisters in a “White Christmas” — “What is a Christmas with no snow?” This writer lives in the South and has just seen his dreams crushed by new probabilities.
In the words of Clark Griswold:“We’re going to press on, and it’s gonna be the hap-hap-hap-happiest Christmas since Bing Crosby tap danced with Danny [bleepin’] Kaye.”

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