Posted at 11:49 AM
Guest post by Rebecca Lindsey, Managing Editor of NOAA's Climate.gov, with contributions from Caitlyn Kennedy and Susan Osborne
Minnesota. Maine. Upstate New York. The Allegheny Mountains of Pennsylvania and West Virginia. Practically anywhere in Idaho. And of course, the Rockies or the Sierra Nevada Mountains. These are the parts of the Lower 48 states where weather history suggests you want to be if you're looking for the best chance of a white Christmas.
The map at right shows the historical probability of there being at least one inch of snow on the ground in the Lower 48 on December 25. (Sorry, Alaska, your historical observation network is too sparse to allow scientists to confidently estimate the probability of a white Christmas across the state’s vast terrain.) Darkest gray shows places where the probability is less than 10 percent. (Sorry West Coast, Gulf Coast, Deep South!) White shows probabilities greater than 90 percent.
If you’d like to pinpoint the probability where you’ll be spending Christmas, you can explore an interactive version of the map at Climate.gov, where you can zoom in to see values for specific stations used to make the map.
These probabilities are based on the latest (1981-2010) U.S. Climate Normals, a data product from NOAA's National Centers for Environmental Information (NCEI). The “Normals” are the latest three-decade averages of several climatological measurements; they are what your local TV weathercaster is referring to when he or she tells you what the day’s normal high and low temperatures are. The collection contains daily and monthly values for temperature, precipitation, snowfall, heating and cooling degree days, frost/freeze dates, and growing-degree days, calculated from observations at approximately 9,800 stations operated by NOAA’s National Weather Service.
Of course, climate history only provides a guide to where snow on the ground is more likely on December 25; the actual conditions on Christmas Day in any year may vary widely because…well, because weather isn’t climate. For prediction of your actual weather on Christmas Day, check out your local forecast at Weather.gov.
If you would like to keep track of the snowfall across the United States on a daily basis, see the National Operational Hydrologic Remote Sensing Center’s National Snow Analyses. For a more detailed explanation of the analysis behind NOAA’s “probability of a white Christmas” map, you can read White Christmas? An Application of NOAA’s 1981-2010 Daily Normals, a scientific paper by NCEI scientists published in the Bulletin of the American Meteorological Society. You can also download a spreadsheet to see the full list of stations and their historical probabilities.
This post was adapted from Climate.gov’s article about the map, which was collaboration between Climate.gov and NCEI. It was first published on December 11, 2013, and is reviewed each year and updated as needed.