1991-2020 Degrees Fahrenheit 1 51.7 49.9 1.8 49 23 1952,1987 1963 1997 1994 top-third 2 58.8 56.1 2.7 61 11 2006 1963 1997 1973 top-third 3 63.1 60.7 2.4 61 10 1992 2021 1997 1983 top-third 4 65.2 63.5 1.7 61 10 1992 1955 1997 1983 top-third 5 65.5 64.5 1.0 54 17 1992 2021 1997 1995 top-third 6 65.2 63.6 1.6 63 8 1992 2021 1997 1988 top-third 7 62.8 61.3 1.5 62 9 1992 1955 1997 1991 top-third 1977,1988 8 59.2 58.0 1.2 58 13 1951,1996 2012 1997 1991 top-third 9 56.6 54.1 2.5 68 3 2014 2012 1997 1998 top-tenth 10 53.3 50.6 2.7 68 2 1979 2012 1997 1998 top-tenth 11 50.8 48.2 2.6 67 3 2014 2012 1997 1998 top-tenth 12 49.3 47.2 2.1 67 3 2014 2012 1997 1998 top-tenth 2002,2017 18 53.5 52.7 0.8 57 12 2014 2012 1997 1955 top-third 2006,2007 24 47.1 47.2 -0.1 43 25 1979 2017 1997 1992 normal 1989,2008 36 46.2 47.2 -1.0 15 51 1979 2000 1997 1995 bottom-third 1959,2010 48 46.6 47.2 -0.6 28 36 1980 2007,2018 1997 1993 normal 1986 60 46.5 47.2 -0.7 22 40 1979 2002 1997 1995 normal