When disaster strikes, state and local governments may request federal aid through a Presidential disaster or emergency declaration. The Federal Emergency Management Agency (FEMA) is responsible for making the federal disaster assistance available. Previously, FEMA did not have an objective basis for declaring federal snow disasters. The National Climatic Data Center (NCDC) and the National Weather Service (NWS) provided FEMA with snowfall extremes and return period statistics, for official weather stations across the contiguous United States and Alaska, to meet this need.
Daily snowfall data from NCDC's TD-3200 data base from the period 1948-1996 were analyzed to produce the statistics provided to FEMA. Three levels of quality control were applied, including ValHiDD processing, internal consistency checks, and outlier checks. Extreme seasonal snowfall and 1-, 2-, and 3-day maximum snowfall totals were computed for about 7,000 National Weather Service Cooperative Stations across the contiguous United States and Alaska. Maximum estimated snowfall amounts for these intervals for return periods of 10, 25, 50, and 100 years were computed for about 5,000 of these stations. The data were analyzed using the generalized extreme-value distribution estimated using the method of L-moments and L-moment ratios.
The dataset developed here provides a comprehensive nationwide picture of extreme snowfall events in a variety of locales, and comprises the most representative national return period snowfall statistics ever computed for non-airport locations. This paper discusses the data, quality control, research methodology, and utilization of the results of this project.