Did a work up of extreme max temps at 4 stations to see how it looked after the mid Dec heat wave. These are the #1 max temps with the most extreme 5+dF being noted. I also noted the 10+dF, and if they are monthly records. The 2021 event was a strong one, and sits in among an elite group of events in the record. Here's the list of 10+ events with (*) being a monthly record. Also the charts.
LaCrosse, WI
March 5, 2000 70 +12
May 31, 1934 107 +13*
Nov 29, 1998 65 +10
Dec 15, 2021 69 +17*
Dec 28, 1984 60 +11
Madison, WI
March 15, 2012 82 +13
March 18, 2012 81 +11
April 22, 1980 94 +11*
May 31, 1934 101 +12*
June 1, 1934 100 +10
Oct 13, 1975 90 +10*
Dec 15, 2021 68 +16*
Dec 28, 1984 62 +10
Lancaster, WI
Jan 1, 1897 60 +13*
Feb 23, 2017 70 +12*
March 4, 1983 67 +10
April 9, 1930 89 +12
May 31, 1934 104 +12*
July 13, 1936 107 +10
Dec 16, 2021 68 +13*
Dec 26, 2019 56 +11
Charles City, IA
Jan 1, 1897 58 +10
Feb 15, 1921 64 +10
Feb 16, 1981 62 +10
March 17, 2012 80 +11
April 6, 1991 89 +11
May 31, 1934 104 +13*
June 8, 1985 102 +10
Dec 8, 1946 63 +10
Dec 15, 2021 68 +15*