Use of mesoscale models to simulate details of upper tropospheric relative humidity (UTRH) fields represents an important step toward understanding the evolution of small-scale water vapor structures that are responsible for cirrus growth and dissipation. Because mesoscale model UTRH simulations require initialization and verification and since radiosonde measurements of relative humidity are unreliable in the upper troposphere, we use GOES 6.7 μm water vapor observations to validate the Pennsylvania State University/National Center for Atmospheric Research nonhydrostatic mesoscale model (MM5) simulations of UTRH. To accomplish this task, MM5 temperature and moisture profiles are used in a forward calculation of the clear-sky 6.7 μm brightness temperature (T6.7), which is converted into UTRH. A statistical analysis is done to evaluate MM5 simulations of T6.7 and UTRH against the GOES 7 observations. For the simulations, an average correlation coefficient of 0.80 was found with a dry bias of 1.6 K. In terms of UTRH, the average correlation coefficient was 0.65 with a dry bias of 3.3%. We also found that MM5 fails to simulate accurately extrema in the UTRH field. ¿ 1997 American Geophysical Union