A Central-U.S. Summer Extreme Dew-Point Climatology (1949-2000)

Abstract

Daily average dew points (DADPs) were examined at 68 central-U.S. weather stations from 1949 to 2000 to identify temporal trends in the occurrence of summer (June—August) extreme surface dew-point days (DADP ≥22°C). Data homogeneity testing revealed that changes in equipment, station location, and instrument height, in addition to calculated DADPs based on available hourly data caused very few statistically significant changes in the data. Temporal patterns based on four 13-yr. periods indicated that much of the Midwest experienced a consistent increase in extreme DADPs through time while those along the Gulf Coast remained generally unchanged. Using accumulated DADP departure from the median graphs, the 52-yr. record was separated into two periods. A comparison of the mean frequency from an earlier (1949-1976) to later (1977-2000) period indicated that the greatest percent increases also occurred in the Midwest. Smaller increases to the south of this area suggest that these increases are not primarily linked to advection from the Gulf of Mexico, rather they are related to changes in a regional moisture source. This moisture source appears to be related to enhanced levels of evapotranspiration from corn and soybean crops, which have experienced a near doubling in total acreage from 1950 to 2000.