An observational analysis of boundary layer moisture evolution during the dryline on 22 May 2002 is presented. This dryline occurred during the International H2O Project (IHOP) and was well observed by a variety of instruments at the intensive observing region (IOR), Homestead site. Although the observed strong upward air motion and the well-mixed boundary layer favored convection, the dryline did not trigger a convective storm. Several operational and research forecast models predicted deep convection at the IOR. High spatial and temporal resolution observational data from National Aeronautics and Space Administration (NASA) lidar instruments, Atmospheric Emitted Radiance Interferometer (AERI), sounding profiles and simulation results are used to investigate the role of moisture during this dryline. It is hypothesized that in addition to convection and lifting, abundant, deep and persistent moisture is required for a dryline to trigger convection. The possible reason why the dryline failed to trigger convection over the IOR is discussed.