1991-2020 Degrees Fahrenheit 1 29.9 35.3 -5.4 13 62 1964 2017 1977 1978 bottom-third 2 20.0 29.9 -9.9 2 73 1984 2017 1979 1978 bottom-tenth 3 15.2 25.7 -10.5 3 72 1984 2015 1979 1978 bottom-tenth 4 13.3 23.8 -10.5 3 70 1992 1999 1979 1978 bottom-tenth 5 17.1 25.1 -8.0 4 69 1992 2018 1973 1978 bottom-tenth 6 21.6 28.3 -6.7 4 69 1992 2018 1973 1978 bottom-tenth 7 26.4 32.3 -5.9 4 69 1992 2018 1973 1978 bottom-tenth 8 30.6 36.1 -5.5 3 70 1992 2018 1973 1978 bottom-tenth 1973 9 34.4 39.4 -5.0 4 69 1992 2018 1973 1978 bottom-tenth 10 37.1 41.6 -4.5 4 69 1992 2018 1973 1978 bottom-tenth 11 38.0 42.5 -4.5 3 70 1992 2018 1979 1978 bottom-tenth 12 38.5 42.5 -4.0 3 70 1984 2018 1973 1978 bottom-tenth 1973 18 35.9 37.8 -1.9 18 53 1993 2018 1977 1978 bottom-third 1961,1962 24 41.1 42.5 -1.4 23 48 1993 2018 1977 1978 bottom-third 1963 36 40.6 42.4 -1.8 14 55 1993,1994 2018 1977 1978 bottom-third 1965,1970,1981 48 40.4 42.3 -1.9 8 59 1976 2019 1977 1978 bottom-third 60 40.3 42.2 -1.9 7 58 1977 2020,2021 1977 1978 bottom-third 1993