Regionalization of snowfall frequency and trends over the contiguous United States

This study examines the regional variations in the frequency of snowfall across the conterminous United States from 1930 to 2007. Principal components analysis and cluster analysis are used to group stations together based on the main modes of variation in snowfall frequency. Results indicate the existence of seven unique snowfall regions, which correspond to predominant storm tracks across the United States. These are the southeast, the south central Plains and southwest, the Ohio River Valley and mid-Atlantic, the Pacific Northwest, and three sub-regions in the Upper-Midwest. Quantile regression reveals that the distribution functions of each region's snowfall frequency are different and in some regions, changing over time. The northern part of the Upper-Midwest is experiencing increasing trends in all percentiles of snowfall frequencies, the Pacific northwest is experiencing declines in greater than median snowfall frequencies, and the southeast is seeing a decline in extreme frequency years. Correlation analysis between large-scale teleconnection patterns and regionally averaged snowfall frequencies corroborate previous findings and indicate specific forcing mechanisms for snowfall frequency in each region.