In the 2020 Hallmark movie "One Royal Holiday," Connecticut is a winter wonderland on Christmas. In fact, snowstorms control much of the plot and end up providing a magical holiday setting that helps the two main characters fall in love.

While it's common in movies, how often does the Nutmeg state actually experience a white Christmas?

The National Atmospheric and Oceanic Administration (NOAA) defines a white Christmas as having at least one inch of snow on the ground at 7 a.m. EST Christmas morning, NOAA experts told Hearst Connecticut Media. Experts measure snow depth, which refers to the amount of snow remaining on the ground, as opposed to snowfall, the amount of snow that rains down in a specific period.

Based on this criteria, the last time the Bridgeport area had a white Christmas was in 2009, when the snow depth was five inches on Christmas Day, according to data from the National Weather Service (NWS) station at Igor I Sikorsky Memorial Airport in Stratford. In the decades prior, there are recorded white Christmases in 1995 and 1980, but the station did not measure the snow depth from 1996-1999.

Bridgeport saw some snow in 2017, 2012, 2008 and 2002, but it didn't accumulate enough to qualify as a white Christmas, according to the weather station.

Up north in the Hartford area, the most recent white Christmas occurred in 2021, with a snow depth of two inches on Christmas Day, according to the NWS station at Hartford-Bradley International Airport in Windsor Locks. Since 1980, a white Christmas has occurred in that area in 2002, 1995 and 1989, with some years experiencing periods of snowfall.

In Burlington, near Hartford, its most recent white Christmases occurred in 2021 and 2017, as well as in 2007, 2008 and 2009, according to the National Weather Service.

The Hartford-Bradley International Airport station didn't record the snow depth between 1996-1999 or from 2007-2016. From 1996-99, NOAA transitioned its primary surface weather observing network (ASOS), and there was no snow reporting during this period, John Bateman, a public affairs officer for NOAA, said.

After a storm brought more than half a foot of snow to some parts of Connecticut early December, residents may be wondering what the chances are for a festive flurry this year.

As of Wednesday, two major weather models forecasted snow for late Christmas Eve into Christmas day.

The Global Forecast Systems model, produced by NOAA's National Centers for Environmental Prediction, projects that most of the state will see around an inch of snow and the northwest corner could see nearly three. The European Center for Medium-Range Weather Forecast model from the United Kingdom lays down around a quarter to a half inch of snow for most of the state, except for the southeast corner on the coast. Both models suggest below-average temperatures on Christmas Day.

On the other hand, NOAA's Climate Prediction Center released its 8-14-day weather outlook for Dec. 24-30 on Monday and it favors higher-than-average temperatures, and also leans towards below-average precipitation in Connecticut.

Apart from temperature, a white Christmas is caused by a combination of other climate factors, such as the emergence of La Niña. The climate phenomenon occurs when the sea surface temperatures in the central and east-central equatorial region of the Pacific Ocean between Peru and Australia are unusually cooler than average. However, it looks like the event will be relatively short-lived and have a weak impact, experts say.

La Niña increases the chances of snow in Connecticut and across the northeastern U.S., but not by a significant amount, Jessica Spaccio, a climatologist at Northeast Regional Climate Center (NRCC) at Cornell University.

The average probability for a white Christmas in Bridgeport from 1991-2020 is 12 percent, but the probability increases to 25 during La Niña years, according to NRCC. For Hartford, that probability goes from 24 to 33.

"La Niña changes the pattern of the jet stream and how storms can come our way. And so sometimes during a La Niña the jet stream will come right across the Northeast, and storms will travel this way and bring snowfall," Spaccio said.

The chances of a white Christmas in Connecticut are dwindling due to climate change, and if the warming trend continues, the festive weather event may only occur in the movies.

Connecticut experienced one of its warmest autumns on record this year and 2024 is set to be the hottest on record for the state. This year's January-through-November period was the warmest on record, according to climate data from the National Centers for Environmental Information.

December 2023 was Hartford's second-warmest December on record and Bridgeport's fifth warmest. And climate change was responsible for warming up the state for nearly half of the month, according to an analysis by Climate Central, a non-profit group made up of scientists and communicators who study how our changing climate impacts people's lives.

The rest of the season is warming as well. Winters in New England are warming faster than in any other area of the contiguous United States, according to a 2024 analysis by the Washington Post. Since 1980, winter in Bridgeport has risen 0.82 degrees Fahrenheit per decade and winter in Hartford has warmed 1.04 degrees. It's unclear what the national rate is.

The proportion of winter precipitation falling as rain rather than snow has increased in the northeastern U.S. and the trend that is projected to continue over this century, according to Climate Central. Warmer winters are also generated by a lack of snow, as snow-free landscapes absorb more sunlight.

The majority of Hartford's winters since 2000, 15 out of 24, have seen snowfall that amounted to less than the winter average of 39.1 inches, according to the National Weather Service.

The milder conditions also lead to fewer days with measurable snow depth, because it melts shortly after hitting the ground, Spaccio said. By 2070, if greenhouse gas emissions continue to increase at the current rate, Connecticut will have less than 30 days of snow on the ground during the winter, according to NRCC predictions in 2019.

This means the region's winter recreation season is likely to become shorter and smaller. Industries like skiing, snowmobiling and ice fishing could face harsh blows, Spaccio said.

"Unfortunately for those that do want a white Christmas. Going forward, it's less and less likely. We've already seen a decrease and we expect that trend to continue," she said.