There’s an actual scientific definition of a ‘white Christmas’

By Allison Chinchar | CNN meteorologist

While nearly 100% of Christmas movies show beautiful blankets of fresh, fluffy snow on Christmas morning, the reality is only about a dozen states have more than a 70% chance of waking up to snow on average each year.

According to the National Oceanic and Atmospheric Administration (NOAA), a “white Christmas” is defined as having one inch or more of snow on the ground Christmas morning.

Statistical data was compiled from the averages of several climatological measurements between 1981 and 2010, including daily and monthly normal temperature, precipitation, snowfall, heating and cooling degree days, frost/freeze dates and growing degree days. They were calculated from observations at nearly 10,000 official weather stations across the country.

While the map shows the climatological probability of snow-covered ground on December 25, the actual conditions on any given year may vary widely. It is also important to note that just because a certain location may have at least 1 inch of snow on the ground doesn’t mean it is fresh snow. That 1 inch could have come down two days prior, but very cold temperatures kept the snow in place for Christmas Day.

Who has the best odds?

For the contiguous United States, the best odds exist in the Mountain West, Upper Midwest and interior portions of the Northeast.

“Aspen, Colorado, is just one of about a dozen locations boasting a 100% historical probability of seeing a white Christmas,” NOAA says on their white Christmas historical site.

Other locations such as Crater Lake, Oregon, Steamboat Springs, Colorado, and Marquette, Michigan, are also high certainty locations.

Or you could head to Hawaii — yes, you read that correctly.

Hawaii’s two mountain peaks, Mauna Kea and Mauna Loa, both which sit at more than 13,000 feet above sea level, are the only two locations that see snow annually in Hawaii. And, yes, both summits have fresh snow on them every single year, mainly because the wet season in Hawaii runs from October to April and temperatures regularly drop below freezing on the summits from November to March.

The summit on Haleakala in Maui, which tops out at over 10,000 feet, can also see some occasional snow cover. The Mauna Kea Weather Center has several live camera feeds you can peak at to see if the summit is covered in snow.

If snow is what you seek, you should probably avoid southern California, lower elevations of Arizona and New Mexico and the Gulf Coast region. Berkeley, California, Tempe, Arizona, and Orlando, Florida, all have a statistical chance of zero percent for having a white Christmas.

However, just because you live in a southern state doesn’t mean a white Christmas is impossible.

In 2010, Atlanta picked up 1.3 inches of snow on Christmas Day.

In 1989, people in Charleston, South Carolina woke up to 4 inches of snow on the ground. Technically, no new snow fell on Christmas Day but was leftover from the day before, since temperatures Christmas Eve night stayed below freezing.

Northern Texas is no stranger to the occasional snowflake on Christmas, but what about farther south near the Mexican border? In 2004, Brownsville, Texas, picked up 1.5 inches of snow on Christmas morning. Nearby South Padre Island picked up 2.5 inches, and Corpus Christi saw 4 inches of powder.

What about Alaska?

Alaska sounds like it would be the most obvious on the NOAA list, right? Interestingly, though, Christmas isn’t the ideal time for snow in Alaska.

“In many locations, October is the snowiest month of the year,” said Brian Brettschneider, a research physical scientist with the National Weather Service. “In the core winter months, the air is so cold that it just cannot hold much moisture. You end up getting a lot of very small snow events.”

In fact, northern Alaska usually has already picked up more than 50% of its seasonal snowfall by Christmas Day. Again, climatology plays a big role in this.

“March-May is the climatologically driest time of year,” Brettschneider said. “Even though the air can hold more moisture by then, and even though it is usually cold enough for snow, there just aren’t any storms to lift the air.”

This is unique compared to almost every other area of the US. For example, St. Louis, Chicago, and Pittsburgh pick up more 70% of their seasonal snowfall after Christmas.

For Boston, New York and Philadelphia, it’s over 80% after the holiday. Raleigh, North Carolina, Memphis, Tennessee, and Norfolk, Virginia, pick up nearly 90% after Christmas.

However, it is Alaska’s remote nature that prevents it from being included on NOAA’s list for a white Christmas.

“The station network in Alaska is too sparse to allow scientists to interpolate with confidence,” NOAA’s climate website states.

Simply meaning, they are excluded from the NOAA white Christmas map because there aren’t enough weather stations that can provide reliable data to predict “white Christmas odds” with confidence.

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