1991-2020 Degrees Fahrenheit 1 59.9 63.3 -3.4 18 58 1997 2018 1954 1959 bottom-third 2 57.9 58.2 -0.3 42 34 1997 1991 1958 1959 normal 1969 3 48.2 52.7 -4.5 2 74 1984 2012 1960 1959 bottom-tenth 4 43.5 47.6 -4.1 2 74 1978 2012 1960 1959 bottom-tenth 5 41.7 44.1 -2.4 15 61 1978 2012,2017 1958 1959 bottom-third 6 40.9 42.5 -1.6 23 52 1978 2012 1959 1957 bottom-third 1964,1969,2001 7 40.8 42.6 -1.8 21 54 1978 2012 1958 1959 bottom-third 1997,2001 8 42.6 44.2 -1.6 21 54 1978 2012 1959 1959 bottom-third 1959,1962 9 45.7 46.7 -1.0 27 48 1978 2017 1959 1957 normal 1971 10 48.9 49.5 -0.6 39 36 1977,1978 2017 1959 1957 normal 1981 11 51.4 51.8 -0.4 43 32 1977 2017 1959 1957 normal 1973,1981,1985,1995 12 53.1 53.5 -0.4 41 34 1977 2017 1959 1957 normal 1988 18 48.9 49.8 -0.9 31 43 1979 2017 1959 1958 normal 24 52.5 53.4 -0.9 22 52 1978 2017 1959 1958 bottom-third 1967,1984,1990,2005 36 52.3 53.4 -1.1 15 58 1979 2018 1960 1959 bottom-third 1969,1971,1983,1994,1997,2015 48 52.7 53.4 -0.7 24 48 1980 2019 1959 1958 bottom-third 1972,1977,1998 60 52.7 53.4 -0.7 25 46 1981 2020 1960 1959 normal 1973,1977