The purpose of the TAMDAR (Tropospheric Airborne Meteorological DAta Reporting) program, sponsored by the FAA's Aviation Weather Research Program (AWRP) with interaction from NASA's Aviation Weather INformation (AWIN) program, is to assess the potential of automated weather reports from aircraft to improve aviation weather services. One facet of this project is to evaluate data sparse regions within the current spectrum of ACARS (Aircraft Communications Addressing and Reporting System) weather observations. An analysis of the spatial and temporal distribution of observations reported by ACARS for the period of May 13, 2001 to June 2, 2001 is presented. Hourly world-wide and CONUS data are examined and stratified by day of week, time of day, and altitude. Large temporal fluctuations are seen in the total number of reports by hour, clearly showing the evening peaks and early morning valleys of commercial air traffic. Additionally, an overall decrease in reports during the weekends is seen, and attributed to a lack of data from package carriers, which generally do not fly during those times. With respect to altitude, reports are examined at 5,000 foot intervals from 0 to 45,000 feet. The bulk of the reports are given at flight levels between 25,000 and 45,000 feet, and coverage within these levels is fairly uniform. Data below 25,000 feet tend to be concentrated near major airport hubs, with only the NE seaboard showing somewhat uniform coverage due to the density of major airports in that area. Placing meteorological sensors and communications on smaller aircraft would greatly enhance the near-surface spatial distribution of ACARS reports, and is the emphasis of the TAMDAR program.