1991-2020 Degrees Fahrenheit 1 62.5 66.4 -3.9 12 56 1973 2004 1977 1986 bottom-third 2 61.0 63.3 -2.3 17 51 1964 2015 1985 1986 bottom-third 3 58.7 61.2 -2.5 11 55 1955 2015 1985 1986 bottom-third 1965,1977 4 57.8 59.8 -2.0 11 51 1973 2015 1985 1986 bottom-third 1965,2002 5 59.0 60.6 -1.6 16 46 1973 2015 1985 1986 bottom-third 2005 6 61.3 63.3 -2.0 10 51 1973 2015 1985 1986 bottom-third 7 64.1 66.9 -2.8 3 58 1973 2015 1973 1986 bottom-tenth 8 67.8 70.3 -2.5 5 56 1973 1996,2015 1985 1986 bottom-tenth 1985 9 70.5 73.0 -2.5 5 56 1973 2015 1985 1986 bottom-tenth 1985 10 72.4 74.6 -2.2 8 53 1973 2015 1985 1986 bottom-third 11 73.0 75.0 -2.0 9 52 1973 2015 1983 1986 bottom-third 12 72.9 74.8 -1.9 11 50 1966,1973 2015 1983 1986 bottom-third 1958 18 69.7 71.1 -1.4 18 38 1973 2015,2016,2018 1986 1985 bottom-third 1988 24 73.6 74.9 -1.3 20 36 1973 2015,2016 1985 1986 normal 1968,1983 36 73.4 74.9 -1.5 15 36 1973 2017 1985 1986 bottom-third 48 73.5 74.9 -1.4 13 33 1974,1975 2018 1986 1985 bottom-third 1985,1988 60 73.3 74.8 -1.5 11 30 1973,1976 2018 1978 1986 bottom-third