1991-2020 Degrees Fahrenheit 1 21.9 26.6 -4.7 13 48 2015 1998 1979 1981 bottom-third 2 19.5 25.7 -6.2 7 54 1979 1998 1979 1981 bottom-third 3 22.5 27.3 -4.8 8 53 1977 2002 1979 1981 bottom-third 4 26.8 30.4 -3.6 10 50 1977 2002 1979 1981 bottom-third 5 31.0 34.6 -3.6 9 51 1977 2002 1979 1981 bottom-third 6 36.0 39.5 -3.5 7 53 1977 2016 1979 1981 bottom-third 7 40.9 44.0 -3.1 7 53 1977 2017 1979 1981 bottom-third 8 44.8 47.5 -2.7 7 53 1977 2017 1979 1981 bottom-third 9 47.4 49.9 -2.5 9 51 1977 2017 1979 1981 bottom-third 1986 10 48.2 50.8 -2.6 6 54 1977 2017 1979 1981 bottom-tenth 11 48.1 50.6 -2.5 7 53 1977 2017 1979 1981 bottom-third 12 47.0 49.3 -2.3 8 52 1979 2013 1979 1981 bottom-third 1966 18 43.6 46.0 -2.4 6 53 1979 2017 1979 1981 bottom-tenth 1966 24 47.2 49.3 -2.1 7 52 1994 2013 1980 1981 bottom-third 1968 36 47.6 49.3 -1.7 8 50 1979 2013 1981 1978 bottom-third 1967,1969,1972,1977,1978 48 47.1 49.3 -2.2 2 55 1980 2013 1980 1981 bottom-tenth 1979 60 47.3 49.2 -1.9 3 53 1981 2002,2013,2020 1981 1980 bottom-tenth 1979,1980