The five month period from May-Sep 1988 was the hottest five month period in Minnesota history, followed closely by 1894. All of the top 20 occurred below 350 ppm CO2.
Hottest 5 month periods in Minnesota Rank Month Year Average maximum Temperature 1 9 1988 80.7922 2 9 1894 79.85 3 9 1936 79.8109 4 9 1933 79.7281 5 9 1976 79.3234 6 9 1931 78.4344 7 9 1939 78.3094 8 9 1921 78.2406 9 9 1934 78.2172 10 9 1922 78.1875 11 8 1988 78.1719 12 9 1955 78.1578 13 9 1987 77.95 14 9 1980 77.6312 15 10 1894 77.5813 16 10 1931 77.5578 17 9 1932 77.4891 18 9 1900 77.4062 19 9 1937 77.2953 20 9 1930 77.2672
