1991-2020 Degrees Fahrenheit 1 57.8 51.6 6.2 91 3 1924 1977 1979 1977 top-tenth 2 50.6 45.1 5.5 90 4 1909 1977 1979 1977 top-tenth 3 39.0 38.1 0.9 69 23 1950 2010 1979 1977 top-third 1988 4 31.1 31.1 0.0 65 27 1917,1950 1998 1979 1977 top-third 5 25.2 26.0 -0.8 56 36 1950 1998 1979 1977 normal 6 23.5 23.6 -0.1 66 24 1950 1998 1979 1958 top-third 7 23.3 24.0 -0.7 60 28 1979 2012 1979 1958 top-third 8 25.1 26.3 -1.2 55 32 1920 2012 1979 1976 normal 1973,2004 9 28.2 29.4 -1.2 52 33 1920 2012 1979 1976 normal 10 31.4 32.8 -1.4 46 38 1920 2012 1979 1976 normal 11 34.6 35.7 -1.1 47 37 1920 2012 1979 1976 normal 1985 12 36.6 37.8 -1.2 42 40 1950,1951 2012 1979 1977 normal 18 29.5 33.1 -3.6 10 69 1951 1999 1979 1978 bottom-third 1960 24 34.9 37.8 -2.9 10 67 1951 1999 1979 1978 bottom-third 36 34.9 37.8 -2.9 5 67 1952 2000 1968 1979 bottom-tenth 48 35.4 37.7 -2.3 7 60 1952 2001 1972 1979 bottom-tenth 1960,1962,1972 60 35.8 37.7 -1.9 17 46 1953 2002 1979 1979 bottom-third 1958,1962,1979