U.S. climate normals: temperature and degree days

Climate Normals of temperature and heating and cooling degree days for over 6,000 stations based on the 1981-2010 time period will be released in the next few months. These Normals will all be based on underlying monthly temperature values that have undergone improved quality control and bias adjustment compared to the temperature data used for prior Normals. The new version will make extensive use of daily temperature data, as opposed to the previous version which primarily used spline fits to compute daily normals from monthly normals. A constrained harmonic fit is utilized to compute daily temperature normals that are consistent with the high quality monthly temperature normals. In addition, heating and cooling degree day normals will be computed in a more direct fashion, replacing the “modified Thom” approach. This talk will address these methodological changes and highlight the differences between the new temperature normals and the old version.