December 17, 2004 — Dreaming of a White Christmas? Well, depending on whom you talk to, that can mean many different things. For some, this question conjures up thoughts of a holiday song and/or film, but for NOAA it has an entirely different meaning. NOAA is more likely to define a “white Christmas” as an inch of snow or more on the ground at 7 a.m. on Christmas morning. Although you will have to wait for the NOAA National Weather Service forecast (or peak out the window on Christmas morning) to obtain information about snow on Christmas Day this year, ever wonder how you can find out if various parts of the country have had a white Christmas in past years?

NOAA Map Showing the Historical Frequency of White Christmases
To help answer this question the NOAA National Climatic Data Center has generated a map from its U.S. Climate Atlas showing the historical frequency (in percent) that a snow depth of at least one-inch was observed on the morning of December 25th (in the past). As you can see from the map to the right, the highest frequencies have been in northern and mountainous areas of the country. The frequency was computed using historical snow depth observations for December 25th for the full period of record for a given station (rather than just the 1961-1990 climatological normals period). This map is just one of 2,023 color maps of climatic elements included in the NOAA Climate Atlas, a CD which contains temperature, precipitation, snow, wind, pressure and other data that best portrays the U.S. climate. The period of record of the data for most of the maps is 1961-1990. See NCDC's sample maps and information about ordering this product. (Click on NOAA image above right for a larger view of the map showing the historical frequency of a snow depth of at least one-inch on Christmas Day. Please credit “NOAA.”)

NOAA Report on Historical Frequency of White Christmases in the Past
NCDC also has a separate “report,” which contains a table showing the historical frequency (in percent) for a snow depth of at least one-inch on Christmas morning, as well as the historical frequencies for a depth of at least five inches and 10 inches. The report also contains several figures showing these historical frequencies for the continental United States with city-by-city plots and with contours at 20 percent intervals. Unlike the map generated from the NOAA Climate Atlas (described above), only first order (i.e., major) stations with at least 25 years of data were used to generate this report and the ’61-’90 period was chosen to coincide with the standard period for computing climatological normals in effect at the time when the report was published. The complete report is available online. (Click on NOAA image above right for a larger view of the map showing the historical frequency of a snow depth of at least one-inch on Christmas Day in 20 percent intervals. Please credit “NOAA.”)

A table and one of the maps in this NOAA report shows that historically there has been a white Christmas (i.e., at least one-inch of snow on the ground by 7 a.m. Christmas morning) 100 percent of the time in two cities in Michigan (Marquette, Mich., and Sault Ste Marie, Mich.), two cities in Minnesota (Hibbing, Minn., and International Falls, Minn.) and in Stampede Pass, Wash. Likewise, there has been at least five inches of snow on the ground in Stampede Pass, Wash. 100 percent of the time and at least 10 inches, 96 percent of the time — making it the U.S. location with the highest historical frequency of having had a white Christmas in the past. However, keep in mind that this statistic was calculated based on snow depth and not necessarily on newly fallen snow. Also, it is important to remember that higher mountain areas (e.g., elevation of 8,000 feet in an area averaging about 4,000 feet) will tend to have higher probabilities for each of the three categories. (Click on NOAA image above right for a larger view of the map showing the historical frequency of a snow depth of at least five inches on Christmas Day in 20 percent intervals. Please credit “NOAA.”)

Generally, the greatest historical frequencies of a white Christmas lie exactly where they would be expected — over the northern United States and in mountainous areas. If a “white Christmas” is defined as having a snow depth of at least one-inch, the historical frequencies of having a white Christmas in the past are 60 percent or better over an area including much of the northern Rockies, the northern Great Plains, the Great Lakes area and most of New England. The historical frequencies are less than 20 percent over most of the southern third of the country (excluding the Rockies), along with the Pacific coast. (Click on NOAA image above right for a larger view of the map showing the historical frequency of a snow depth of at least 10 inches on Christmas Day in 20 percent intervals. Please credit “NOAA.”)

Note that these historical frequencies are based on long-term climatology and NOT on current weather patterns (i.e. this article describes the historical odds of a white Christmas, not the forecast of a white Christmas this year). The actual conditions you will experience on Christmas morning may vary widely from the probabilities presented in both the NOAA Climate Atlas (CD) and the NOAA report described above. The snow on the ground or snowfall on Christmas day will depend on the actual weather pattern during that time. These historical frequencies should only be used as a guide to show where snow accumulation (snow on the ground) has been most prevalent in the past. To obtain the latest weather forecast for your area, contact your local NOAA National Weather Service forecast office. Note that extended range — out to seven days — forecasts from the NOAA Weather Forecast Offices provide a more realistic white Christmas outlook and useful travel weather information for the days leading up to Christmas day.

If you desire further data related to these tables and figures, please contact NCDC (phone: 828-271-4800, fax: 828-271-4876, internet: orders@ncdc.noaa.gov). This report, including images, is also available in color on the NCDC home page.

Other Related NCDC Products
NCDC also has several other climatological products that may give additional clues as to where snow was likely to have occurred in the past:

• National Weather Service Snow Normals 1971-2000: NCDC has produced National Weather Service Snow Normals 1971-2000 for more than 500 major U.S. locations. They are available without charge. A climate normal is defined, by convention, as the arithmetic mean of a climatological element computed over three consecutive decades. Snow normals were computed for mean snowfall (503 stations), mean snow depth (267 stations), number of days with snowfall greater than or equal to 0.1" (525 stations), and number of days with snowfall greater than or equal to 1.0" (525 stations).
• Comparative Climatic Data: NCDC also produced another set of 17 climatic tables called the Comparative Climatic Data. The online version is available without charge and contains monthly mean data for over more U.S. cities. Temperature, degree days and precipitation normals, means and extremes; as well as wind, humidity, sunshine and cloudiness tables are provided.
• NOAA Operational Daily Snow Analysis Charts: If you would like to keep track of the snowfall across North America on a daily basis, see the NOAA Operational Daily Snow Analysis Charts.
• Other NCDC Snow Related Web Resources: Both the U.S. Snow Monitor and a snow climatology can both can be accessed from the NCDC Climate Monitoring Reports and Products Web page. The snow monitor is updated daily with snow fall and snow depth observations from the NWS COOP network stations of the contiguous United States in near real time. The snow climatology page contains a background discussion on the Snow Climatology Project, National Snow Extremes Table and State Snow Climatology and Extremes.

Weather Records on Christmas Day
According to an NCDC data source of approximately 275 first order NOAA Weather Service locations, the U.S. location with the greatest snow depth accumulation (most snow on the ground) on Christmas day was Kalispell Glacier Airport in Montana with a total of 125 inches on the ground in 1902. The U.S. location with the greatest snow falling on Christmas day was Valdez, Alaska, with a total of 29 inches falling that day in 1929. The U.S. cities with the coldest and warmest temperatures on Christmas day were Gulkana Airport in Alaska (with -64 degrees F in 1917) and San Juan, Puerto Rico (with 90 degrees F in 1989), respectively.

Other NOAA Snow Related Activities
NOAA is involved in a number of other snow related activities. Specifically, NOAA maintains three major programs to monitor and model snowpack characteristics for the nation. The NOAA National Weather Service’s volunteer Cooperative Observer Program is a network consisting of about 11,000 stations with historical snowfall records. A second network consists of approximately 275 first order National Weather Service offices whose data are printed in the local climatological data publication. Lastly, the NOAA National Operational Hydrologic Remote Sensing Center maintains an Airborne Snow Survey Program and uses ground-based, airborne and satellite snow data to model high resolution snowpack characteristics for the continental United States.

NOAA also established the National Snow and Ice Data Center (Boulder, Colo.) a national information and referral center in support of polar and cryospheric research. NSIDC archives and distributes digital and analog snow and ice data. It also maintains information about snow cover, avalanches, glaciers, ice sheets, freshwater ice, sea ice, ground ice, permafrost, atmospheric ice, paleoglaciology and ice cores.

Relevant Web Sites

NOAA Satellite and Information

NOAA National Weather Service

NOAA OHRSC Interactive Snow Information

NOAA OHRSC National and Regional Snow Analyses

NOAA OHRSC Airborne Gamma Snow Survey

NOAA HPC Winter Weather Forecasts

NOAA Storm Watch

Media Contact:
John Leslie, NOAA Satellite Service, (301) 457-5005