With the sponsorship of the Federal Aviation Administration, MIT Lincoln Laboratory is developing the Graphical Weather Service (GWS), a data link application that provides near-real-time ground-based weather information to pilots. Through the use of GWS, the pilot will be able to access both graphical and text weather information for any location in the contiguous United States. In-cockpit access to near-real-time weather information may substantially affect the situational awareness and subsequent decision making of pilots. In developing and evaluating this service, a human factors approach has been taken. This paper is an overview of the human factors activities performed in the development and evaluation of GWS.