The U.S. Army forts recorded daily (or up to three per day) weather observations starting in the early 1800s. Many of these records continue into the mid-1800s. In the mid- to late 1800s, other voluntary observers were managed by the Smithsonian Institution and the U.S. Department of Agriculture. Weather observations at these stations typically included precipitation and temperature, recorded 3 times a day, especially for the earlier periods, and later, daily maximum and minimum temperature. At some stations, observations were also taken of cloud cover, wind direction and movement, barometric pressure, and dry-and wet-bulb temperatures, from which relative humidity was calculated. These station networks eventually evolved into the Weather Bureau's Cooperative Observer Network. The National Climatic Data Center (NCDC) holds these 1800s records on microfilm. As part of NCDC's Climate Data Modernization Project, these records have been scanned and indexed, and will be made available online to the research community. Many of the daily records are also being digitized. Approximately 160 stations (about 3 per state) have been selected for digitization, with more stations to be digitized as funding permits. Over 30 distinct data types have been identified for digitization. Quality assurance will be applied to the digitized data. Significant changes in instrumentation and observation practices occurred during the period covered by this data set. A comprehensive set of metadata will be developed to complement the data set. When completed, this digitized data set will allow for extension of the analysis of daily climate variables back into the 1800s and will provide a link between the more recent instrument records and paleoclimate records. Additional data sources are being located and added to this data periodically.