Why would they only use the 3 full decades of temps to come up with the average when it would be more accurate to use all temps ever recorded? Mike Collins
Posted December 27, 2006
1. Establishing comparative climatological values that are standardized from one region or location to another, so that you don't end up trying to compare likely conditions at station A with a 37-year history against station B that has been around for 72 years, for example, and
2. As a compromise between wanting the "normals" to include a significant period of time long enough to be reflective of a full or nearly full range of potential year-to-year variability in weather conditions for the location of interest while at the same time being short enough to be sensitive to real changes in the climatology of a given location, whether those changes might be due to local/regional urbanization and building patterns, natural cycles like the Pacific Decadal Oscillation or multidecadal sea surface temperature variations in the Atlantic, or large-scale variations associated with anthropogenic gas and particulate emissions.