1991-2020 Degrees Fahrenheit 1 55.3 49.9 5.4 66 6 1952 1963 1972 1971 top-tenth 2 58.7 56.2 2.5 62 10 1976 1963 1972 1971 top-third 1953 3 63.2 60.7 2.5 65 6 1992 2021 1972 1963 top-tenth 4 65.4 63.5 1.9 64 7 1992 1983,2021 1972 1963 top-tenth 2005 5 66.0 64.5 1.5 64 7 1992 2021 1972 1963 top-tenth 1988,2010 6 64.2 63.6 0.6 52 19 1967,1992 2021 1972 1963 top-third 7 61.5 61.3 0.2 48 23 1992 2021 1972 1970 top-third 1999 8 59.0 58.0 1.0 57 14 1951 2012 1972 1963 top-third 9 55.3 54.1 1.2 60 11 1951 2012 1972 1973 top-third 10 52.0 50.6 1.4 62 8 1979 2012 1972 1973 top-third 2010 11 48.8 48.2 0.6 54 16 2014 2012 1972 1955 top-third 1955,1995 12 47.4 47.2 0.2 48 22 2014 2012 1972 1955 top-third 1953 18 52.5 52.7 -0.2 43 26 2014 2012 1972 1964 normal 1964,1992,2011,2019 24 46.3 47.2 -0.9 29 39 1979 2017 1972 1956 normal 1977,1985 36 46.1 47.2 -1.1 24 42 1979 2000 1972 1957 normal 1976,1977,1996 48 45.9 47.2 -1.3 19 45 1979,1980 2007,2018 1972 1958 bottom-third 1974,1975,1977,1996 60 45.7 47.2 -1.5 16 46 1979 2002 1972 1968 bottom-third 1968,1997