Jun | Feb | Mar | Apr | May | June | July | Aug | Sep | Oct | Nov | Dec | |
1970-1979 | −4.6 | −20.9 | −22.3 | −21.9 | −35.6 | −50.3 | −57.0 | −52.7 | −37.1 | −17.4 | −10.1 | −7.6 |
1980-1989 | −4.1 | −2.6 | −21.8 | −32.6 | −34.8 | −50.7 | −58.7 | −52.5 | −37.6 | −28.2 | −6.2 | −7.4 |
1990-1999 | −9.1 | −4.4 | −7.8 | −28.3 | −42.5 | −46.9 | −56.3 | −45.5 | −42.7 | −21.2 | −24.7 | −6.7 |
2000-2016 | −15.1 | −14.7 | −11.9 | −22.7 | −34.3 | −34.5 | −50.7 | −49.8 | −42.7 | −28.8 | −26.2 | −12.1 |
N = Average (D) | −8.2 | −10.5 | −16.0 | −26.4 | −36.8 | −45.6 | −55.7 | −50.1 | −40.2 | −23.9 | −16.8 | −8.5 |