Based on the CET temperature serie since 1900.

Cool Summers with an average temperature of 15.0°C
Total 39 years or 1 in 3 years

YEAR , JUNE , JULY , AUGT , SUMM
1902 , 13.9 , 14.7 , 14.3 , 14.30
1903 , 13.0 , 15.3 , 14.3 , 14.20
1907 , 12.4 , 14.1 , 14.3 , 13.60
1908 , 14.3 , 15.8 , 14.6 , 14.90
1909 , 11.8 , 14.6 , 15.4 , 13.93
1910 , 14.7 , 14.2 , 15.2 , 14.70
1912 , 13.9 , 16.1 , 12.9 , 14.30
1913 , 14.3 , 14.6 , 15.2 , 14.70
1915 , 14.4 , 14.6 , 15.3 , 14.77
1916 , 11.8 , 15.3 , 16.4 , 14.50
1918 , 13.3 , 15.4 , 16.1 , 14.93
1919 , 14.3 , 13.9 , 15.7 , 14.63
1920 , 14.4 , 14.1 , 13.6 , 14.03
1922 , 13.8 , 13.7 , 13.6 , 13.70
1924 , 13.9 , 15.3 , 14.1 , 14.43
1927 , 12.6 , 15.9 , 15.7 , 14.73
1928 , 12.9 , 16.1 , 15.3 , 14.77
1929 , 13.3 , 16.0 , 15.4 , 14.90
1931 , 14.4 , 15.3 , 14.4 , 14.70
1946 , 13.1 , 16.3 , 14.7 , 14.70
1948 , 13.5 , 15.8 , 15.1 , 14.80
1954 , 13.4 , 14.2 , 14.6 , 14.07
1956 , 13.1 , 15.8 , 13.5 , 14.13
1962 , 13.7 , 15.1 , 14.5 , 14.43
1963 , 14.9 , 15.2 , 14.3 , 14.80
1965 , 14.7 , 14.0 , 14.9 , 14.53
1971 , 12.4 , 16.9 , 15.6 , 14.97
1972 , 11.8 , 15.6 , 15.1 , 14.17
1974 , 13.9 , 15.2 , 15.2 , 14.77
1977 , 12.2 , 15.9 , 15.2 , 14.43
1978 , 13.7 , 14.8 , 15.0 , 14.50
1980 , 13.8 , 14.7 , 15.9 , 14.80
1981 , 13.2 , 15.5 , 16.2 , 14.97
1985 , 12.7 , 16.2 , 14.6 , 14.50
1986 , 14.8 , 15.9 , 13.7 , 14.80
1987 , 12.8 , 15.9 , 15.6 , 14.77
1988 , 14.4 , 14.7 , 15.2 , 14.77
1993 , 15.0 , 15.2 , 14.6 , 14.93
2011 , 13.8 , 15.2 , 15.4 , 14.80