1991-2020 Degrees Fahrenheit 1 51.3 52.5 -1.2 45 40 1978 2017 2015 2019 normal 2 51.7 50.6 1.1 67 18 1978 2017 2019 2017 top-third 3 51.9 50.5 1.4 71 14 1978 2017 2019 2017 top-third 1971,2013 4 52.6 52.1 0.5 62 23 1978 2017 2019 2018 top-third 1971 5 55.5 55.3 0.2 64 21 1977 2017 2019 2018 top-third 1952,1954 6 60.4 59.3 1.1 74 11 1977 2017 2019 2017 top-third 7 64.1 62.9 1.2 75 10 1977 2017 2019 2017 top-third 8 66.6 65.6 1.0 76 9 1977 2017 2019 2017 top-third 2005 9 68.0 67.4 0.6 74 10 1977 2017 2019 2019 top-third 1955,1957,2005,2019 10 68.9 68.1 0.8 75 9 1977 2017 2018 2019 top-third 2006 11 68.6 68.0 0.6 75 9 1977 2017 2019 2017 top-third 2006,2022 12 67.6 67.3 0.3 69 15 1977 2017 2015 2019 top-third 18 64.8 64.6 0.2 71 13 1978,1984 2017 2015 2019 top-third 2022 24 67.8 67.3 0.5 74 9 1978 2017 2016 2019 top-third 1999 36 67.8 67.2 0.6 74 8 1979 2018 2016 2019 top-tenth 2000,2007 48 68.5 67.2 1.3 79 2 1980 2019 2018 2019 top-tenth 60 68.7 67.2 1.5 79 1 1962,1963 2020 2019 2020 highest