You talk about weather records in the Chicago area going back to the 1800s, how was that data collected and how accurate is it?
Chicago’s official weather records date back to November 1870, and before that, a variety of incomplete observations have been found dating back to the 1830s or earlier. From 1870-1925, the city’s official weather records, while accurate, were all taken at a variety of observation sites, all near Lake Michigan. The proximity of the official thermometer to the lakefront has skewed that data with generally cooler summers and warmer winters. Rainfall and snowfall data, were measured in about the same manner today’s manual observations are obtained. While Chicago’s official precipitation and temperatures records date back to late 1870, the city’s snowfall climatology did not begin until the fall of 1884.