The wind-forced detachment and movement of soil particles, is known for having important regional and global implications on climate change and biogeochemical cycles. The wind erosion process occurs when wind speed exceeds a certain threshold value, which depends on a number of factors, including surface soil moisture. In arid regions changes in atmospheric humidity contribute to most of the variability in surface soil moisture, which, in turn, has a significant influence on wind erosion threshold. This paper investigates the dependence of wind erosion threshold on air humidity in two arid regions in North America, the Mojave Desert (CA) and Canyonlands (UT). Field data are used to test existing models relating the threshold velocity for wind erosion to atmospheric conditions. The threshold velocity is found to be significantly dependent on the atmospheric relative humidity (RH) and to exhibit a well-defined maximum for RH ≈ 35%. This result validates at the field scale recent theories and laboratory-scale experimental results.