In previous columns you’ve mentioned that the Chicago climate normals are updated every 10 years. When will they be updated next?
The current “normal” temperatures are, by definition, temperatures calculated over the 30-year period 1981-2010. The normals are recalculated once every 10 years and will next be updated for the period 1991-2020. This is in keeping with United Nations World Meteorological Organization standards. Normal temperatures are calculated for each day of the year, and the results are smoothed so the daily values steadily rise or fall creating a smooth annual curve. Normals are also computed for a multitude of other meteorological events, including precipitation, snowfall, wind, and specific temperature benchmarks such as days of 90s, 100s, sub-freezing or subzero.