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How has your odds of a white Christmas changed?

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

So cross your fingers and use the map below to see if there’s at least a small chance of building Frosty on Christmas Day.

Most likely there is snow on the ground Christmas Day is about where you expect it to be; parts of North Dakota, Minnesota and Wisconsin have a higher than 90% chance, along with upstate New York and interior New England.

It is cold in the western mountainous areas, with a high possibility of snow on December 25.

But what is not clear from the map above is where these probabilities have changed. CNN has collected numbers for more than 2,000 locations that have had a white Christmas opportunity in NOAA’s regular data.

A staggering 64% of those locations are less likely to have a White Christmas in the new normal than the previous 30-year average (taking into account the weather from 1981 to 2010).

Only 31% of the stations increased their probability, and 4% of the positions remained the same.

Rebecca Lindsey from NOAA writes: “If you want to compare two maps for signs of the effects of long-term warming, keep a few things in mind. “From a standard 30-year period to the next, two decades of data are the same; only one out of three decades is new.”

This means that the change from one normal to another can be relatively small since you change only a third of the data. “It also means that in some locations the changes may be the result of natural degenerate variability,” says Lindsey.

Take, for example, New York City in the first half of the 20th century, where you can see this decadent transformation taking place. Around 1940, when Irving Berlin wrote the song “White Christmas,” a decade had passed since it snowed for Christmas in New York City, where he lived.

The city saw an impressive series of white Christmases from 1911 to 1920 and then again in the late 40s. After a lull, the 1960s produced a fantastic decade. another for snow at Christmas in Central Park.

After that, the pattern switched to a much less frequent span. And there have only been four white Christmases in New York City since 1970. As of 2009, the “Miracle on 34th Street” city has had no snow on the ground for Santa to land.

You can’t build the same timeline for every location. In many places, weather data was sparse prior to the 1980s. But the trends seen here in this new set of white Christmas probabilities echo changes scientists have seen across the United States. .

“The spatial fingerprint of climate change that we expect based on our modeling studies is visible in National models of temperature change and precipitation Indicator“, Lindsey wrote. So it’s not surprising that there are some slight differences between the 1981-2020 version of the white Christmas map and the 1991-2020 version consistent with the realities of long-term warming. ”
For instance, areas in the South used to have at least a small chance of seeing snow on Christmas Day. But that chance has faded in the latest data. It makes sense when you look at how average temperature in december has warmed all over the Southeast.

The link between temperature has varied greatly across the United States. The only region showing cooler average temperatures in the new benchmark data is the Northern Plains, where the chance of a white Christmas also increases.

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

It may take another decade or two of writing to know exactly how much of an impact the climate crisis will have on your white Christmas dreams. But don’t use Scrooge fully – there are always exceptions.

“While the map shows the historical probability that at least 1 inch of snow will be observed on December 25, the actual conditions in any given year can vary widely from these conditions. as current weather patterns will determine snow on the ground or snowfall on Christmas Day,” adds optimistic Lindsey. “These probabilities are only useful as a guide to indicate where there is more snow on the ground.”

And if you’re still wondering – like the Haynes sisters in a “White Christmas” – “What is Christmas without snow?” Let’s take that from a writer who lives here in the South and has just seen his dreams dashed with new probabilities: A Christmas without snow is still Christmas!
In the words of Clark Griswolds: “We’ll move on, and we’ll have the happiest Christmas since Bing Crosby danced with Danny. [bleepin’] Kaye. “

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