The design and preliminary tests of an automated differential absorption lidar (DIAL) that profiles water vapor in the lower troposphere are presented. The instrument, named CODI (for COmpact DIAL), has been developed to be eye safe, weatherproof, and portable. The lidar design and its unattended operation are described. Nighttime intercomparisons with in situ sensors and a radiosonde are shown. The instrument design goal is a compact, lower cost, and lower resolution DIAL that can be duplicated and deployed, ideally alongside boundary layer radar wind profilers, in unattended arrays. Such a network could measure horizontal water vapor transport in the lower atmosphere useful for better quantitative precipitation forecasts, and observations of long-term trends in the water vapor field needed for climate studies.