| Jun | Feb | Mar | Apr | May | June | July | Aug | Sep | Oct | Nov | Dec | |
| 1970-1979 | 8.8 | 11.9 | −1.2 | 19.8 | 1.6 | −6.9 | −33.1 | −40.10 | −27.1 | −10.7 | −6.4 | −7.8 |
| 1980-1989 | 0.1 | −3.4 | −12.7 | −8.6 | −7.8 | −29.2 | −45.8 | −44.3 | −28.6 | −9.3 | −3.6 | −11.0 |
| 1990-1999 | −0.5 | −4.7 | −1.7 | −3.4 | −14.0 | −28.5 | −43.7 | −36.9 | −17.2 | −20.8 | −3.4 | −5.9 |
| 2000-2016 | −3.1 | −0.1 | −3.0 | −12.1 | −8.1 | −28.4 | −40.4 | −31.3 | −25.4 | −7.5 | −1.9 | −2.7 |
| N=Average(D) | 2.8 | 1.2 | −5.2 | 2.5 | −6.7 | −21.5 | −40.9 | −40.4 | −24.3 | −13.6 | −4.4 | −8.2 |