1991-2020 Degrees Fahrenheit 1 66.0 64.7 1.3 53 23 1997 2018 1949 1950 top-third 2 58.8 60.8 -2.0 17 59 1961 1991 1950 1949 bottom-third 1975,1980,1995 3 52.8 55.9 -3.1 9 67 1971 2012 1950 1949 bottom-third 1983 4 49.3 51.5 -2.2 18 58 1958 2012 1950 1949 bottom-third 1989 5 48.6 48.2 0.4 58 18 1978 2012 1948 1949 top-third 6 47.2 46.6 0.6 58 18 1978 2012 1948 1949 top-third 1954,1999 7 46.9 46.6 0.3 54 21 1963,1977,1978 2012 1950 1949 top-third 1992 8 48.8 47.9 0.9 61 14 1977 2012 1949 1949 top-third 1949 9 50.5 50.2 0.3 53 21 1977 2017 1950 1950 top-third 10 53.0 52.6 0.4 55 19 1977 2017 1950 1950 top-third 1957 11 55.3 54.7 0.6 58 16 1977 2017 1950 1950 top-third 1953,2000 12 57.0 56.2 0.8 62 12 1977 2017 1950 1950 top-third 1954,1992,2006 18 54.0 53.0 1.0 68 6 1978 2017 1950 1950 top-tenth 1974,2013,2018 24 -99 56.1 -99 -99 -99 1978 2017 normal 36 -99 56.1 -99 -99 -99 1979 2018 normal 48 -99 56.1 -99 -99 -99 1980 2019,2020 normal 60 -99 56.1 -99 -99 -99 1981 2020 normal