National Overview - January 2014
New CONUS Temperature Dataset

« National Overview - January 2014

New CONUS Temperature Dataset

In early 2014, NCDC will switch to a new dataset as its official monitoring data to determine the contiguous United States (CONUS) temperature. This new dataset is dervived from a gridded instance of the Global Historical Climatology Network (GHCN-Daily). The same underlying dataset will inform NCDC's climate division monitoring products (more information about the climate division transition, nClimDiv, is available here). This page deals only with the CONUS temperature transition.

For several years, NCDC has used a 2.5° longitude by 3.5° latitude gridded analysis of monthly temperatures from the 1,218 stations in the the US Historical Climatology Network (USHCNv2.5) for its CONUS temperature. The new dataset is based on interpolation to a much finer-mesh grid (about 5km by 5km) that incorporates values from several thousand more stations available in the the GHCN-Daily dataset. In addition, monthly temperatures from stations in Canada and Mexico near the U.S. border are used to aid in the interpolation of U.S. anomalies near the U.S. borders.

The switch to the GHCN-Daily-based dataset has little effect on the average national temperature trend or on relative rankings for individual years. This is because the new dataset is based on gridded anomalies produced using the same set of algorithms and corrections that are applied in the production of the USHCN v2.5 dataset. However, although both the USHCN v2.5 and the new gridded dataset yield comparable trends, the finder resolution dataset more explicitly accounts for variations in topography (e.g., mountainous areas). Therefore, the baseline temperature, to which the national temperature anomaly is applied, is lower (cooler) in nClimDiv than in the USHCN v2.5. This new baseline affects anomalies for all years equally, and thus does not alter our understanding of trends.

There are a number of peer-reviewed articles that describe the USHCN and its algorithms, available through the USHCN web page. The algorithms described in these articles have not changed. A more detailed description of the nClimDiv dataset, is available as Vose et al., 2014. Interested users are encouraged to read Vose et al., 2014 and its citations for further information.