Many investigators have used near-surface air temperature measurements to document a downward global trend in the diurnal temperature range (DTR). In this paper, we use radiosonde-based tropospheric measurements to examine vertical dimensions in trends in the DTR over the central United States. We find declining trends in DTR only at 85 kPa and the surface in the high-sun season, with the absolute trend at 85 kPa being greater than the trend at the surface suggesting that the trend in DTR is far more than an urban artifact in the data. There are no significant trends in DTR from 70 kPa to 25 kPa in any season. These results suggest that DTR trends in the low troposphere are likely influenced by near-surface processes such as variations in cloudiness, vegetation, or precipitation but not dominated by urban effects.