An accurate knowledge of the vertical potential temperature gradient within the stable boundary layer (SBL) is important for modeling plume rise within the SBL and for determining the critical dividing streamline height in complex terrain situations. The U.S. Environmental Protection Agency’s (EPA’s) ISCST3 model assumes a neutral lapse rate for stability classes A through D, and assumes values of 0.02 K/m for E stability and 0.035 K/m for F stability. The EPA has recently proposed replacing the ISCST3 model with the AERMOD model for certain applications. The AERMOD model incorporates improved knowledge of the planetary boundary layer structure based on similarity theory, and can also utilize more extensive observations of meteorological parameters, including vertical temperature profiles. This paper presents comparisons of observed temperature profiles with theoretical temperature profiles using data obtained from field studies, including the Full Scale Plume Study conducted at the Tracy Power Plant site located east of Reno, Nevada. The sensitivity of dispersion modeling results to the vertical temperature profile is also presented.