Trends in Extreme Temperatures and Dry Periods in the Northeastern United States

A continuous, homogenized set of daily minimum and maximum temperature and precipitation data from 40 weather stations throughout the northeastern United States is used to analyze temporal trends and spatial patterns in extreme temperatures and dry periods. Time series of various lengths were used, with the long-term from 1899-2008 and the short-term from 1970-2008. Trends in extreme temperature were analyzed by counting the annual occurrence of extreme maximum and minimum temperatures exceeding high (99th, 95th, & 90th) and falling below low (10th, 5th, & 1st) percentile thresholds. Changes in precipitation were analyzed by counting the number of dry days (no recorded precipitation) by season. Linear regressions were used to show changes. Warming trends occur at 75% of this study’s stations in the 1st and 99th percentile of both minimum and maximum temperature from 1970 to 2008, analogous to the increasing trend of mean global temperature exhibited over the same time period. Winter minimum temperature extremes show the most consistent warming trends across the Northeastern US, with all but two stations showing a decrease in the number of days falling below their respective 1st percentile minimum temperature thresholds. The strongest warming trends occur at inland stations from 1970 to 2008. Statistically significant trends (p<0.10) range from -0.1 to -1.9 days/decade. Dry days in summer (Jun-Aug) show consistent trends, with 80% of stations experiencing fewer dry days from 1970 to 2008. Statistically significant trends in dry days range from +2.0 to -4.0 days/decade.