Climate Matters has expanded geographically, so we updated our historical chance of a White Christmas analysis to 244 cities in the U.S. — covering all Nielsen markets. White Christmas is defined here as having at least an inch of snow on the ground on Christmas Day. In addition, the analysis includes the record highest snow depth
in each city on Christmas Day.But as the world warms, the overall area of North America covered by snow is decreasing. One reason is because an increasing percentage of winter precipitation is falling as rain instead of snow in many locations. A Climate Central report found that between sea level and 5,000 feet in elevation across the Western U.S., a smaller percentage of winter precipitation is falling as snow.
However, the relationship is more complex at each local level. Rising temperatures can cause some individual storms to produce more snow, where temperatures are still well enough below freezing. That’s because for every 1°F rise in temperature, the atmosphere can hold 4 percent more water vapor. In turn, more water is available to fall as snow or rain.
METHODOLOGY: The White Christmas graphic illustrates the probability of 1”+ of snow depth based on analysis of the 1981-2010 NOAA/NCEI climatological normal. Record snow depth for each city comes from the Applied Climate Information System. North American snow cover data is from Rutgers University Global Snow Lab. Each point represents the average annual snow depth from July to June. Data begins in 1973, when satellite resolution was upgraded for suitable snow depth mapping accuracy.