The United States Climate Reference Network (USCRN) goal is to document long-term climate behavior in accordance with the 1999 Climate Monitoring Principles certified by the National Research Council. Front-end USCRN scientific success is based upon careful and rigorous selection of appropriate instrument monitoring sites. The primary variables to be monitored are the air temperature and the precipitation. The plan is for about 100 USCRN stations to be deployed across the United States by about 2007. A secondary grid of 75 stations has been envisioned for Alaska, Hawaii, and perhaps Puerto Rico and the Virgin Islands. 50+ USCRN stations are now operating. Two experimental stations are also operating in severe environments in Alaska.

Criteria for USCRN sites targeted for operations during the next 50-100 years are very exacting. They exceed WMO standards for climate monitoring and station siting. This paper discusses primary climate station siting criteria: proper instrument and site exposures; land use and land tenure stability; avoidance of built-up areas and areas of future development; avoidance of agriculture, irrigated areas, and large artificial water bodies; regional climate representativiness with respect to temperature and precipitation; avoidance of localized microclimates, and consistent site maintenance and instrument re-calibrations. Examples are given of sites and locations sensitive to climate change and of sites representing special circumstances and environments.