1991-2020 Degrees Fahrenheit 1 40.5 38.2 2.3 59 18 1978 1976 2016 2019 top-third 2 40.5 36.6 3.9 70 7 1978 2017 2019 2017 top-tenth 3 41.0 37.4 3.6 72 5 1977 2017 2019 2017 top-tenth 4 41.2 39.6 1.6 61 15 1977 2017 2019 2017 top-third 5 45.1 43.1 2.0 67 9 1977 2017 2019 2017 top-third 1991 6 50.1 47.3 2.8 72 3 1977 2017 2019 2017 top-tenth 7 53.7 51.2 2.5 73 2 1977 2017 2019 2017 top-tenth 8 56.8 54.3 2.5 73 2 1977 2017 2019 2017 top-tenth 9 58.4 56.3 2.1 73 2 1977 2017 2019 2017 top-tenth 1950 10 59.4 57.1 2.3 73 2 1977 2017 2019 2017 top-tenth 11 59.4 57.1 2.3 73 2 1977 2017 2019 2017 top-tenth 12 58.1 56.2 1.9 72 3 1977 2017 2019 2017 top-tenth 18 55.0 53.2 1.8 72 2 1978 2017 2019 2017 top-tenth 1992 24 57.5 56.1 1.4 70 4 1978 2017 2019 2018 top-tenth 36 57.2 56.1 1.1 69 4 1979 2018 2017 2019 top-tenth 48 57.7 56.1 1.6 71 1 1980 2020 2019 2020 highest 60 57.7 56.0 1.7 70 1 1981 2020 2019 2020 highest