Many Coloradans dream of a white Christmas, but the chances of that happening in the Denver metro area this year are slim.Before making any predictions, let's get on the same page about what a white Christmas actually is.The National Weather Service (NWS) defines a white Christmas as "1 inch or more of snow on the ground Christmas morning." The map from the NWS shows the average probability of a white Christmas across the country. The closer to white an area is, the closer to a 100% chance of a white Christmas. So in Colorado's mountains, you're almost guaranteed a white Christmas. Crested Butte has a 99% chance of a white Christmas, according to the National Oceanic Atmospheric Administration (NOAA).In the southeastern corner of the state, it's closer to a 20% chance. And in Denver, it's between a 40% and 50% chance. That could mean a light shower later in the day.The map is just an average, so what actually happens will change from every year.For example, last year, it snowed in the metro on Christmas Eve. The day after Christmas, the northeastern plains saw blizzard conditions. But on Christmas Day itself, no snow was recorded on the ground at Denver International Airport. So even though it was snowy elsewhere, it doesn't go down in history as a white Christmas, at least in Denver.Most major U.S. cities historical chances of seeing a white Christmas are well below 50%, according to NOAA. And it's incredibly rare to have snowfall on Christmas in back-to-back years. It's only happened twice in Denver, most recently in 2014 and 2015.