Trends In Wintertime Climate Variability In The Northeastern United States: 1970- 2004

Humans experience climate variability and climate change primarily through changes in weather at a local and regional scale. One of the most effective means to track these changes is through detailed analysis of meteorological data. In this work, changes in the winter climate of the northeastern United States are documented. Snow on the ground and snowfall are important components in water management, travel safety, and winter tourism and recreation. Trends in Temperature, snowfall, and snow depth data were collected from the United States Historical Climate Network (USHCN). The months of December through March are selected for winter climate analysis. Monthly and seasonal time series of the number of days with snow on the ground greater than 1, 3, and 5 inches are constructed from snow depth data. The National Climatic Data Center and Carbon Dioxide Information Analysis Center perform extensive quality assurance and quality control measures for monthly temperature data. However, daily snowfall and snow depth data have not been adjusted for station relocations, instrument changes, or time of observation biases. To address these data quality issues, we evaluate daily data for spatial coherence with nearest neighbors, and remove stations with non-climatic influences from regional analysis. Monthly and seasonal trends in mean, minimum and maximum temperature, total snowfall, and days with snow on the ground are estimated using linear regression and robust spline analysis. Northeastern United States winter temperatures are warming at a rate significantly greater than the global average. At stations located north of 44oN, December snowfall exhibits a decreasing trend (-3.5 inches/decade), whereas March snowfall is increasing (+1.3 inches/decade) over the period 1970-2004. Across the northeastern United States, the number of days with snow on the ground has also decreased substantially. The results hold important implications for the winter economy and recreation in the region.