1991-2020 Degrees Fahrenheit 1 39.0 35.3 3.7 62 11 1960 2012 2003 2000 top-third 2 31.4 29.1 2.3 54 19 2014 2012 2003 2000 top-third 3 26.3 25.7 0.6 48 24 1979 2012 2003 2002 top-third 4 26.6 25.4 1.2 51 21 2014 2012 2003 2002 top-third 1968,1990 5 28.6 27.6 1.0 51 21 2014 2012 2003 2002 top-third 6 32.2 31.3 0.9 51 21 2014 2012 2003 2002 top-third 1957 7 36.2 35.8 0.4 50 22 2014 2012,2016 2003 2002 top-third 8 40.8 40.0 0.8 51 20 1978 2012,2017 2003 2002 top-third 1987 9 44.1 43.5 0.6 50 21 2014 2012 2003 2002 top-third 10 46.3 46.0 0.3 44 27 2014 2012 2003 2002 normal 2007 11 47.1 47.2 -0.1 41 30 2014 2012 2003 2002 normal 1955 12 47.2 47.2 0.0 41 30 2014 2012 2003 2002 normal 2018,2021 18 41.3 41.9 -0.6 30 40 1979 2017 1998 2003 normal 1957,1967 24 46.9 47.2 -0.3 38 31 2015 2017 1998 2003 normal 1958,1991 36 47.8 47.2 0.6 54 13 1979 2018 2003 2002 top-third 1956,1989,2008,2012 48 47.2 47.2 0.0 44 21 1980 2002,2019 1999 2003 top-third 1955,1958,1991,2014,2017,2021 60 47.6 47.2 0.4 52 11 1979 2020 2001 2003 top-third 1992