ASHRAE Research Project RP-1613 prepared an update of the climatic design conditions for the "Climatic Design Information" chapter of ASHRAE Handbook—Fundamentals and for ANSI/ASHRAE Standard 169, Weather Data for Building Design Standards. This update resulted in an increase of the number of stations to 6443 (a 16% increase compared to 2009) and the inclusion of precipitation data used in particular to determine climate zones in energy standard ANSI/ ASHRAE/IES Standard 90.1. A more recent period of record (1986–2010 for most stations) was used to incorporate changes in the climate. Compared to the previous edition, climatic design temperatures are generally slightly higher, cooling degree are slightly higher, and heating degree-days are lower, which is indicative of a general warming of the climate. In addition, RP-1613 prepared an update of theWeather Data Viewer, a stand-alone product used by engineers to access the full single- and joint-frequency distributions of all the climatic design parameters listed inASHRAE Handbook— Fundamentals, as well as additional parameters, such as temperature bin data and wind roses. Part two of the paper, "Revising ASHRAE Climatic Data for Design and Standards— Part II: Clear-Sky Solar Radiation Model," provides a detailed description of the changes made to the clear-sky solar radiation model.