1991-2020 Degrees Fahrenheit 1 39.8 38.2 1.6 54 23 1978 1976 1960 1957 top-third 2 33.3 36.6 -3.3 19 58 1978 2017 1958 1960 bottom-third 3 32.1 37.4 -5.3 7 70 1977 2017 1961 1960 bottom-tenth 4 35.8 39.6 -3.8 9 67 1977 2017 1961 1960 bottom-third 5 40.2 43.1 -2.9 15 61 1977 2017 1958 1960 bottom-third 6 45.2 47.3 -2.1 16 59 1977 2017 1958 1960 bottom-third 2001 7 49.6 51.2 -1.6 20 55 1977 2017 1959 1960 bottom-third 1969 8 52.6 54.3 -1.7 17 58 1977 2017 1958 1960 bottom-third 9 54.7 56.3 -1.6 21 54 1977 2017 1959 1960 bottom-third 1981 10 55.4 57.1 -1.7 13 62 1977 2017 1961 1960 bottom-third 11 55.7 57.1 -1.4 24 51 1977 2017 1959 1960 bottom-third 1969,1975 12 53.8 56.2 -2.4 6 69 1977 2017 1961 1960 bottom-tenth 18 51.6 53.2 -1.6 17 57 1978 2017 1959 1960 bottom-third 1971 24 55.0 56.1 -1.1 23 51 1978 2017 1959 1960 bottom-third 36 54.7 56.1 -1.4 14 59 1979 2018 1961 1960 bottom-third 1983 48 54.8 56.1 -1.3 17 55 1964,1980 2020 1961 1960 bottom-third 1967,1985 60 54.9 56.1 -1.2 19 52 1981 2020 1961 1960 bottom-third 1977,1978