This winter’s normal high/low temperatures in Chicago bottomed out at 31/16. I remember it was 28/12 in the 1970’s. Has it really increased by 3-4 degrees in the last 40 years?
Yes it has. By international convention, normal temperatures are computed every 10 years covering the most recent 30-year period of record, so the city’s current normals are based on the climatological data from 1981-2010. The previous normals based on the 1971-2000 data—had the city’s annual temperature cycle bottoming out on January 15-16 with a high of 28 and a low of 12. When the current normals were released in 2011, the city’s winter temperatures increased and snowfall decreased as the trio of severe winters in the late 1970s were removed from the data set.