Water vapor is one of the most important variables in the atmosphere. Only accurate air humidity measurements will reveal the role of water vapor in long-term climate monitoring trends. The objective of this study is to investigate the feasability of transferring air humidity measured in one climate monitoring network to another. The study focuses on air humidity sensors used in three major surface climate observation networks in the Unite States: Automated Surface Observing System (ASOS); Automated Weather Station System (AWS); and the new U.S. Climate Reference Network (CRN). Both ambient air temperature and air humidity are two main components for air humidity transformation. In addition, other microclimate factors such as ambient wind speed, solar radiation, and precipitation (liquid and solid), and barometric pressure are included in this transformation study. The transformation of air humidity measurements will improve the continuity of climate data and the traceability of long-term climate changes in the U.S.