Soundings of the boundary layer were created by combining Wyoming King Air aircraft data with data from surface stations located under the flight tracks. The idealized daytime fair-weather convective boundary layer has constant profiles of temperature and specific humidity throughout the mixed layer. Observed profiles often did not fit this idealized model, even when it was expected. The author found that the vertical variation of specific humidity matches this idealized model most closely during conditions of strong winds, strong sensible heat fluxes, and weak latent heat fluxes. If surface data are used to refine estimates of lapse rates, operational meteorologists should be able to increase the accuracy in convective storm forecasting.