What has been Chicago’s coldest summer, historically? Do we know what caused those conditions?
Defining summer as June, July and August, 1875 was Chicago’s coldest summer. It averaged 66.6 degrees, more than five degrees below the current average summer temperature of 71.8 degrees and all three months were well below normal. It is important to remember that back then, the city’s official thermometer was located near the lake at Madison and LaSalle. There were no 90s that summer, the city’s only one, dating back to 1871, with the highest temperature of 89 on June 11. June was especially cool, logging five days in the 50s, the chilliest just 52 degrees on June 13. July and August combined to produce six days with high in the 60s. Not surprisingly, rainfall was above normal with measurable rain on 40 days.