1991-2020 Degrees Fahrenheit 1 16.1 18.9 -2.8 28 44 1977 2006 1972 1975 normal 2 21.0 21.6 -0.6 36 36 1977 2002 1974 1975 normal 3 27.4 26.6 0.8 50 22 1977 2002 1975 1958 top-third 1958 4 33.6 32.4 1.2 53 19 1977 2002 1975 1964 top-third 1989 5 38.3 38.4 -0.1 43 29 1977 2016 1975 1974 normal 6 43.7 43.7 0.0 46 25 1977 2002 1975 1974 normal 1998 7 47.7 47.7 0.0 45 26 1977 2002 1975 1974 normal 2003 8 50.3 50.3 0.0 45 26 1977 2002,2017 1975 1974 normal 2018 9 51.5 51.2 0.3 49 22 1977 2002 1975 1964 top-third 1980,1988 10 50.5 50.9 -0.4 38 33 1977 2002 1975 1974 normal 1974 11 48.1 49.4 -1.3 20 51 1977 2013 1973 1975 bottom-third 1969,1990 12 45.7 47.2 -1.5 20 51 1952 2013 1973 1975 bottom-third 18 44.7 46.0 -1.3 24 45 1979 2017 1973 1975 normal 1962 24 45.8 47.2 -1.4 24 45 2015 2013 1973 1975 normal 36 46.4 47.2 -0.8 33 34 1963,1979 2013,2018 1975 1958 normal 2015 48 46.0 47.2 -1.2 21 44 1962,1963,1979,1980 2002 1973 1975 bottom-third 60 46.1 47.2 -1.1 23 40 1963 2003 1975 1975 normal 1975