1991-2020 Degrees Fahrenheit 1 49.0 49.3 -0.3 52 33 1983 2021 1997 1996 normal 2 53.4 52.9 0.5 61 24 2000 2021 1997 1996 top-third 1996 3 58.4 57.6 0.8 69 16 1976 2021 1997 1994 top-third 1973,2005 4 64.2 62.7 1.5 77 8 1976 2021 1997 1984 top-tenth 5 68.2 66.9 1.3 76 9 1976 2021 1997 1984 top-third 1984 6 71.6 69.7 1.9 80 5 1976 2015 1997 1998 top-tenth 7 73.4 71.3 2.1 79 5 1976 2015 1997 1998 top-tenth 8 73.9 71.6 2.3 79 5 1976 2015 1997 1998 top-tenth 9 72.7 70.9 1.8 77 7 1976 2015 1997 1998 top-tenth 10 71.0 69.7 1.3 77 7 1976 2011,2016 1997 1998 top-tenth 2010 11 69.3 68.1 1.2 76 8 1983 2016 1997 1998 top-tenth 12 67.8 66.4 1.4 78 6 1940 2016 1997 1998 top-tenth 2021 18 67.8 67.5 0.3 69 15 1968 2016 1997 1998 top-third 24 66.1 66.4 -0.3 64 19 1979 2017 1997 1955 top-third 1955 36 65.7 66.3 -0.6 56 26 1960,1961 2017 1997 1956 top-third 2002 48 65.7 66.3 -0.6 55 26 1961 2018 1997 1957 top-third 1954,2003,2004 60 65.7 66.2 -0.5 53 27 1962 2019,2020 1997 1957 normal 1955