The area of insignificant or negative temperature trends across the southeastern United States, or “warming hole,” has received much attention in recent years. With many meteorological stations sited at low elevations and within urban settings, a closer examination of temperature changes across elevation within the southern Appalachian Mountains is a useful contribution to better understanding the warming hole. Mean monthly maximum and minimum air temperature data were analyzed for 20 stations from the Global Historical Climatology Network spanning the 50-year period of 1967-2016. Stations with continuous coverage varied in elevation from 200-1200 m above sea level. Statistically-significant linear trends by individual station illustrate that southern Appalachian stations experienced increasing mean monthly air temperatures over 1967-2016. For maximum temperature, stations sited at 200-600 m exhibited a mean trend of +0.19 °C/decade, and out of 80 monthly time series analyzed, 20 are statistically significant (p-value ≤ 0.05). At the higher station elevation range of 600-1200 m, 7 of 42 time series are statistically significant with a mean trend from all stations of +0.15 °C/decade. For minimum temperature within the 200-600 m station range, 40 of 80 time series are statistically significant with a mean trend of +0.30 °C/decade. Stations at 600-1200 m exhibited a mean trend of +0.23 °C/decade, and of those, 17 of 42 trends are statistically significant. The decadal trends of mean monthly maximum and minimum air temperature were compared for the two overlapping 30-year periods of 1967-1996 and 1987-2016. The mean of the 30-year trends in maximum temperature for stations located at 200-600 m elevation decreased from +0.19 to +0.12 °C/decade from the early to the latter of the 30-year time periods. Meanwhile, the mean of the 30-year trends in maximum temperature for stations sited within 600-1200 m elevation increased from +0.08 to +0.18 °C/decade. For minimum temperature, the mean trend for stations in the 200-600 m elevation range increased from +0.18 to +0.35 °C/decade. Meanwhile, the mean trend in minimum temperature for stations at 600-1200 m elevation increased from +0.20 to +0.31 °C/decade between the overlapping time periods. While monthly variability in the degree of warming is present, the largest changes in decadal trends generally occurred during the transitional months of autumn and spring. These results highlight overall warming within the southern Appalachian Mountains despite cooling trends previously described for the surrounding southeastern United States.
Keywords: southern Appalachians, mountain meteorology, sky islands, regional climate change