VARIABILITY IN HIGH-TEMPERATURE EXTREMES IN THE SOUTHEASTERN UNITED-STATES

Forty-one years of data from 13 first-order National Weather Service stations in the southeastern United States were analyzed to determine the spatial variability in the frequency and duration of hours and days when temperatures were greater-than-or-equal-to 32-degrees-C (high-heat). Spatial analysis indicated that extreme high temperature characteristics from individual stations should not be combined into a regional or statewide average. For determining high-heat scenarios, May through September (summer) average maximum temperature (Tmax) was found to be a more appropriate indicator of high-heat conditions than the average temperature (Tmean). Comparing conditions in average warm and cool summer seasons indicated that: (1) increases in the frequency and duration of high-heat hours and days from cool to warm summer seasons range from 70 to 997%; (2) the number of high-heat hours per day increases significantly (27 to 118%) from cool to warm summer seasons; (3) increases in Tmax from cool to warm summer seasons are greater than increases for Tmean; (4) Tmean values underestimate the number and duration of high-heat events; and (5) the diurnal temperature range increases during warm summer seasons. These results show that great variability already exists in today's climate characteristics, and that any potential shift in average temperature will cause even greater changes in the frequency and duration of extreme high temperatures in this region.