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Time series of observed seasonal temperature data from selected locations on the American Great Plains contain a great deal of information on the nature and scales of climate variations over the past century. At four long-term stations in eastern Colorado, trends of increasing mean maximum and minimum temperatures occurred in all seasons except autumn; with most warming preceding 1940. Diurnal range has been decreasing considerably in recent decades, but long-term trends are not consistent at all locations. Interannual variability has also been changed but does not show a systematic trend.
Time series similarities across the Great Plains decay rapidly over short distances in and near the Rocky Mountains, but are well correlated over longer distances in a north-south direction parallel to the mountains. The shared variance of mean seasonal temperatures decreased by 50% over a north-south distance of approximately 350 miles. Significant year-to-year differences in north-south and plains-mountains temperature gradients occur across the Great Plains. Changes in north-south winter temperature gradients appear to be related to Rocky Mountain precipitation patterns and other indicators of large scale atmospheric circulation patterns. Such connections offer explanations for variations that occur on an interdecadal time scale.