Temperature measurements within 200 mi of the airport, and for altitudes up to 60,000 ft, will be necessary for calculating the fuel requirements of supersonic transports. In order to determine an adequate time and space separation for these measurements, a detailed knowledge of the mesoscale variability of temperatures in such regions is necessary. This paper, based on a series of approximately 300 radiosonde flights launched within 50 mi of Ft. Sill, Okla., during March and April 1958, presents the root mean square changes in temperature with time up to 6 hr and with distance up to 50 mi for every thousand feet from the surface to 60,000 ft. Temperature variability increases with time to a maximum of 3.5C at 6 hr at 37,000 ft. The variability increases with distance below 20,000 ft to a maximum of 3.0 C at 50 mi separation. Above 20,000 ft, temperature variability increases to a maximum of 2.5C at 40 mi and 45,000 ft, and then decreases.