Songwriter Irving Berlin dreamed of a “White Christmas.” The National Oceanic and Atmospheric Administration (NOAA) went even further and calculated the historical probability of a white Christmas for the entire contiguous United States.

PHOTOS: Snowflakes Up Close and Personal

During the past 30 years, folks in the Rocky Mountains region, the upper Midwest and inland New England frequently fulfilled their dreams of a snowy Noel. Down in Dixie, from the Missouri boot heel to Florida, there was almost no chance of a white Christmas, barring the intervention of Snow Miser from the classic children’s special, “The Year Without a Santa Claus.”

NOAA’s map (shown above) shows the likelihood of having at least one inch of snow on the ground on December 25. NOAA climatologists created the map using data from 1981 to 2010. The measurements came from approximately 9,800 NOAA-operated weather stations. The scientists used a combination of daily and monthly normals of temperature, precipitation, snowfall, heating and cooling degree days, frost/freeze dates, and growing degree days, which is a calculation used to predict plant and animal development rates that are influenced by the weather.

ANALYSIS: Ice Age Drove Split Between Reindeer and Caribou

The map only provides probabilities of a snowy Christmas, not an actual forecast. To check actually conditions for Christmas in the United States, the National Weather Service’s website provides these maps of precipitation and temperature forecasts for December 25.

IMAGE: National Oceanic and Atmospheric Administration