National Temperature Index
Since 1987, the National Oceanic and Atmospheric Administration's (NOAA's) National Climatic Data Center (NCDC) has used observations from the U.S. Historical Climatology Network (USHCN) to quantify national- and regional-scale temperature changes in the conterminous United States (CONUS). To that end, USHCN temperature records have been "corrected" to account for various historical changes in station location, instrumentation, and observing practice. The USHCN is actually a designated subset of the NOAA Cooperative Observer Program (COOP) Network. The USHCN sites having been selected according to their spatial coverage, record length, data completeness, and historical stability. The USHCN, therefore, consists primarily of long-term COOP stations whose monthly temperature records have been adjusted for systematic, non-climatic changes that bias temperature trends.