Recent trends in maximum and minimum temperature threshold exceedences in the northeastern United States

Abstract

Changes in the annual number of daily maximum and minimum temperature threshold exceedences between 1951 and 1993 are assessed at a network of 22 primarily rural sites in the northeastern United States. After adjusting the annual time series for changes in observation time and eliminating stations at which nonhomogeneous time series were detected, annual time series of the number of days with maximum temperatures ≥ 35.0°, 32.2°, and 29.4°C (95°, 90°, and 85°F); maximum temperatures ≤ 0.0°, -6.7°, and -12.2°C (32°, 20°, and 10°F); minimum temperatures ≥ 23.8°, 21.1°, and 18.3°C (75°, 70°, and 65°F); and minimum temperatures ≤ -12.2°, -15.0°, and -17.8°C (10°, 5°, and 0°F) are statistically analyzed. Overall, a statistically significant trend toward fewer cold minimum temperature threshold exceedences is detected across the region over the period from 1959 to 1993. All stations show a decreasing trend in days with minimum temperatures ≤ -15.0°C over this time period, with significant (α = 0.10) trends present at nearly 50% of the sites. Similarly, significant increases in the exceedence of warm minimum temperature thresholds are evident at more stations than can be expected by chance. A significant number of trends toward fewer warm maximum temperature threshold exceedences is also detected over the 1951-1993 time period. However, these trends are most likely due to changes in the attributes of the individual stations. Only three northern stations show significant increases in cold maximum temperature threshold exceedences.