Autumn range in temperature is defined as the difference between the hottest and coldest temperature during the September 1 through November 30 time period each year.  Climatologists define the seasons on a monthly basis so Autumn is defined as September 1 through November 30, and NOT September 21 through December 21. 

The larger the number on the graph, the larger the range or difference in temperature during that season. 

Autumn 1887 had the largest observed range in Autumn temperatures of 109 degrees

09/12/1887:  94F    11/27/1887: -15F  = 109 degree range