The National Weather Service (NWS) is responsible for the operation and maintenance of a nationwide volunteer network of weather observation, known as the Cooperative Observers Network (COOP). It provides daily weather observations from 11,400 stations nationwide. The core network contains about 7,000 stations, which report maximum and minimum temperatures, daily precipitation, including liquid equivalent of frozen precipitation, snowfall and snow depth, and the occurrence of special phenomena such as thunder, fog, damaging winds, hail, etc. The remaining 4,400 stations report daily precipitation, evaporation, river stage levels, or some combination of these and other weather parameters. Under the current plans for modernization, COOP stations will use automated sensors to support seasonal, inter-annual climate forecasts, as well as short range forecast verification. The new network will be designed under a prescribed set of requirements which include the presence two sites per NWS forecast zones, with one site per 20mile x 20mile grid over contiguous United States and at least 40 evenly distributed sites per WSR-88D radar umbrella. In order to support agricultural requirements, there will be at least one site per 60m x 60m grid in agriculturally sensitive areas. These stations will monitor soil temperature, soil moisture, temperature, precipitation, evaporation, wind and radiation. In the process of modernization the movement of existing sites will be minimized, to allow overlap between current and modernized observations, in order to retain climatological homogeneity. The first objective under the NWS COOP Modernization Initiative is to determine the optimum distribution of COOP stations to fulfill these requirements.