1991-2020 Degrees Fahrenheit 1 30.5 34.7 -4.2 25 60 1977 2023 1961 1962 bottom-third 2 31.5 37.5 -6.0 10 75 1977 2016 1961 1962 bottom-third 3 35.7 41.4 -5.7 6 79 1977 2002,2016 1948 1962 bottom-tenth 4 41.3 46.0 -4.7 7 78 1977 2002 1945 1962 bottom-tenth 5 46.2 51.0 -4.8 4 80 1977 2016 1945 1962 bottom-tenth 6 50.7 55.5 -4.8 2 82 1977 2016 1963 1962 bottom-tenth 7 54.1 58.8 -4.7 2 82 1977 2016 1963 1962 bottom-tenth 8 56.5 60.7 -4.2 2 82 1977 2016,2017 1963 1962 bottom-tenth 9 57.3 61.0 -3.7 5 79 1941,1977 2016 1959 1962 bottom-tenth 10 56.8 60.3 -3.5 3 81 1941 2016 1959 1962 bottom-tenth 1948,1959 11 55.4 58.8 -3.4 4 80 1941 2007,2017 1959 1962 bottom-tenth 1951,1959 12 53.5 56.9 -3.4 5 79 1941 2013,2017 1959 1962 bottom-tenth 1951 18 53.9 56.4 -2.5 15 68 1945,1964 2017 1959 1962 bottom-third 24 54.4 56.9 -2.5 10 73 1942 2007,2013 1949 1962 bottom-third 1970,1980 36 54.2 56.8 -2.6 4 78 1943 2013 1946 1962 bottom-tenth 1946,1965,1981 48 54.7 56.8 -2.1 18 63 1944 2013,2014 1962 1961 bottom-third 1959,1979,1980 60 54.3 56.8 -2.5 3 77 1945 2021 1948 1962 bottom-tenth 1946