High-precision (~0.5 K) measurements of OH Meinel (M) (6,2) rotational temperatures above the Bear Lake Observatory, UT (42 ¿N, 112 ¿W) during October 1996 have revealed an interesting and unexpected mean nocturnal pattern. Ten quality nights (> 100 h) of data have been used to form a mean night for autumnal, near-equinoctial conditions. The mean temperature and RMS variability associated with this mean night were 203¿5 K and 2.4 K, respectively, and compare very favorably with expectations based on Na-lidar measurements of mean tidal temperature perturbations over Urbana, IL (40 ¿N, 88 ¿W) during the fall 1996. Furthermore, this comparison shows that the 8-h tide was the dominant source of the mean nocturnal temperature variability in the OH M region during this period. Additional data, obtained at Fort Collins, CO (41 ¿N, 105 ¿W) in November 1997, illustrate the occurrence of an 8-h component of OH temperature variability about two months after the equinox and show that daily amplitudes as high as ≅15 K are possible. ¿ 2000 American Geophysical Union