In a valley, such as Monument Valley, winds tend to blow up the valley during the daytime as the air is being heated, and down the valley at night as the air cools. Temperature and relative humidity have much less an effect on sound propagation than wind. The most prominent effect is that of a temperature inversion. A temperature inversion is when the air is cooler aloft than it is at the ground. This is a common occurrence in the Colorado Springs area.
Temperature inversions exaggerate the upwind and downwind phenomenon discussed above.
The measurement of temperature inversions requires measurement of temperature at multiple elevations in the atmosphere, and was beyond the scope of this study. Referring back to Figures 4 and 17, the traffic patterns on I-25 and on local roads do not fully account for the relatively high noise levels measured during the a.m. rush hour. Also, noise levels do not drop off after the p.m. rush hour as traffic volumes would dictate. It is believed that northerly winds are responsible for both of these phenomenon. On a typical early morning in Monument Valley, the atmosphere is relatively calm, there is a good chance that a temperature inversion is in place, and winds are blowing out of the north.