1991-2020 Degrees Fahrenheit 1 56.7 51.2 5.5 71 5 1968 2018 1961 1957 top-tenth 2 51.2 49.4 1.8 57 18 1977,1978 1950 1961 1957 top-third 3 50.5 49.6 0.9 56 19 1977 2017 1961 1957 top-third 1954,1997,2009 4 52.7 51.1 1.6 62 12 1977 2017 1961 1957 top-third 2020 5 54.9 54.1 0.8 54 20 1977 2017 1961 1957 top-third 6 58.5 57.8 0.7 56 18 1977 2017 1961 1957 top-third 7 61.4 61.2 0.2 52 22 1977 2017 1961 1957 top-third 1986 8 63.9 63.8 0.1 50 24 1977 2017 1961 1957 top-third 1986 9 65.3 65.6 -0.3 49 25 1977 2017 1961 1957 normal 2007,2009 10 65.7 66.3 -0.6 38 36 1977 2017 1961 1960 normal 1971,1989 11 65.2 66.1 -0.9 25 49 1977 2017 1958 1961 normal 1975,1985,1990 12 64.7 65.4 -0.7 30 44 1977 2017 1961 1960 normal 1965,1989,1990 18 62.0 62.8 -0.8 32 40 1977 2017 1961 1960 normal 1995 24 64.3 65.4 -1.1 16 56 1977 2017 1962 1961 bottom-third 1981,1998 36 64.5 65.3 -0.8 20 50 1970 2018 1961 1961 bottom-third 1961,1985,1990,1994,1998,2015 48 64.6 65.3 -0.7 23 45 1970 2019,2020 1961 1960 normal 1995,1997,1998 60 64.4 65.3 -0.9 19 47 1970 2020 1962 1961 bottom-third 1963,1983,1997