Using daily data from the United States Historical Climatology Network (USHCN) database, variations and trends in snowfall were examined for the winters of 1948/49 through 2004/05; 1948 being the first year of record for many of the USHCN stations. The winter season was considered to extend from September through May, as many high-elevation and northern stations can receive snowfall very early/late, and we wanted to investigate possible variations in this phenomenon. Although the daily version of the USHCN contains records from 1062 stations, we only retained records from 276 stations for our analysis. This resulted from examining only stations north of 35°N and our fairly stringent requirements pertaining to the amount of allowable missing data over the 57 winters analyzed. A snowfall event (snow day) at a station was defined to be a day with 0.5” of snowfall or greater.

Main findings of the analysis over the period of record include: (1) large decreasing trends in snow days and snowfall over much of the Pacific Northwest (continuing a trend that has been recognized for several years); (2) decreasing trends in snow days (although not snowfall amount) over parts of the central plains and much of the Midwest; (3) increasing trends in snow days and snowfall at most stations in a region stretching from northern North Dakota, across the northern Great Lakes, and eastward to New York; and (4) increasing trends in snow days and snowfall over an area extending from the Rocky Mountains of northern New Mexico, eastward into Oklahoma. Decreasing snowfall in the Pacific Northwest was found to be driven mainly by decreases in January, February, and March. Decreases in snow days over the central plains and Midwest were driven mainly by decreases near the beginning and end of the winter season (November and March), and were related to a later onset (earlier end) of snowfall in the fall (spring) over these regions. Increasing snowfall trends across the aforementioned northern regions were found to be mainly due to January increases.