| Year | Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | Annual |
| 1961 | 8.12 | 5.57 | 5.53 | 1.18 | 1.79 | 5.50 | 3.07 | 1.19 | 7.49 | 2.84 | 3.89 | 8.06 | 54.23 |
| 1962 | 4.04 | 1.59 | 1.82 | 4.89 | 4.84 | 4.95 | 4.13 | 1.20 | 6.64 | 2.10 | 4.77 | 3.81 | 44.78 |
| 1963 | 1.09 | 2.91 | 0.66 | 4.64 | 1.00 | 6.75 | 2.61 | 2.15 | 1.90 | 0.04 | 4.63 | 2.53 | 30.91 |
| 1964 | 5.23 | 2.40 | 3.56 | 7.56 | 3.41 | 2.04 | 0.10 | 2.43 | 4.27 | 1.91 | 2.21 | 3.39 | 38.51 |
| 1965 | 3.93 | 4.61 | 5.13 | 1.87 | 9.87 | 5.24 | 3.02 | 1.44 | 5.54 | 0.29 | 2.55 | 6.72 | 50.21 |
| 1966 | 7.54 | 4.44 | 1.75 | 8.56 | 7.16 | 2.38 | 1.58 | 6.05 | 2.50 | 2.58 | 1.08 | 5.36 | 50.98 |
| 1967 | 0.99 | 3.74 | 2.01 | 2.01 | 4.78 | 2.94 | 4.66 | 1.30 | 0.69 | 2.36 | 0.64 | 5.29 | 31.41 |
| 1968 | 7.28 | 3.36 | 2.68 | 10.57 | 8.25 | 9.21 | 3.46 | 1.38 | 8.00 | 1.68 | 6.46 | 6.24 | 68.57 |
| 1969 | 1.70 | 6.66 | 8.46 | 7.32 | 7.03 | 0.76 | 2.69 | 1.56 | 2.44 | 3.53 | 2.35 | 4.28 | 48.78 |
| 1970 | 1.57 | 4.64 | 4.74 | 2.70 | 4.79 | 1.08 | 0.00 | 3.22 | 2.98 | 6.91 | 1.71 | 1.74 | 36.08 |
| 1971 | 0.42 | 2.23 | 0.55 | 0.62 | 5.07 | 1.74 | 3.75 | 3.05 | 4.26 | 3.73 | 3.94 | 5.52 | 34.88 |
| 1972 | 4.85 | 0.91 | 3.52 | 4.02 | 1.46 | 5.08 | 7.65 | 1.81 | 3.25 | 8.59 | 3.77 | 3.76 | 48.67 |
| 1973 | 5.42 | 1.81 | 7.66 | 6.46 | 2.90 | 7.04 | 1.72 | 4.39 | 6.67 | 6.22 | 4.19 | 4.88 | 59.36 |
| 1974 | 9.75 | 1.41 | 1.24 | 4.26 | 5.42 | 2.22 | 4.32 | 5.54 | 8.62 | 2.76 | 7.08 | 3.43 | 56.05 |
| 1975 | 2.71 | 12.80 | 4.48 | 3.64 | 6.77 | 7.66 | 1.38 | 1.95 | 1.58 | 4.59 | 4.31 | 2.60 | 54.47 |
| 1976 | 1.43 | 2.11 | 4.22 | 2.80 | 6.04 | 4.98 | 3.44 | 0.55 | 2.42 | 2.38 | 2.09 | 4.95 | 37.41 |
| 1977 | 3.53 | 2.30 | 4.07 | 3.22 | 1.18 | 3.49 | 1.24 | 3.80 | 2.36 | 1.40 | 2.81 | 2.91 | 32.31 |
| 1978 | 6.66 | 2.61 | 2.58 | 3.57 | 2.77 | 2.03 | 1.09 | 1.57 | 2.14 | 0.95 | 5.40 | 3.50 | 34.87 |
| 1979 | 7.20 | 5.85 | 6.53 | 4.28 | 13.74 | 5.01 | 6.24 | 3.24 | 4.87 | 5.02 | 7.02 | 3.57 | 72.57 |
| 1980 | 4.01 | 1.89 | 3.75 | 4.48 | 6.18 | 1.59 | 1.58 | 2.29 | 1.76 | 2.26 | 3.49 | 1.23 | 34.51 |
| 1981 | 2.14 | 3.70 | 3.33 | 1.11 | 5.50 | 4.41 | 8.01 | 1.51 | 6.17 | 5.91 | 3.28 | 0.66 | 45.73 |
| 1982 | 3.08 | 2.18 | 4.25 | 10.78 | 3.45 | 7.23 | 2.89 | 0.23 | 2.65 | 5.58 | 6.31 | 8.73 | 57.36 |
| 1983 | 1.44 | 5.77 | 4.66 | 0.90 | 7.58 | 5.13 | 1.15 | 2.90 | 2.14 | 1.21 | 4.21 | 7.07 | 44.16 |
| 1984 | 1.81 | 5.77 | 3.52 | 1.66 | 2.39 | 1.12 | 4.15 | 0.87 | 3.23 | 13.33 | 2.90 | 2.74 | 43.49 |
| 1985 | 3.66 | 4.72 | 4.39 | 6.94 | 4.64 | 0.94 | 4.60 | 2.74 | 3.54 | 8.41 | 7.40 | 2.23 | 54.21 |
| 1986 | 0.44 | 2.55 | 0.30 | 4.86 | 7.72 | 9.37 | 2.87 | 2.96 | 3.26 | 6.03 | 7.11 | 5.41 | 52.88 |
| 1987 | 1.26 | 5.84 | 2.07 | 0.50 | 1.93 | 5.33 | 3.65 | 1.27 | 2.83 | 2.11 | 7.70 | 5.21 | 39.70 |
| 1988 | 1.39 | 1.63 | 4.25 | 1.40 | 0.43 | 0.14 | 4.21 | 4.86 | 2.04 | 2.67 | 2.18 | 3.08 | 28.28 |
| 1989 | 10.21 | 2.10 | 6.29 | 0.89 | 6.47 | 10.30 | 3.86 | 1.04 | 4.06 | 2.08 | 2.04 | 1.68 | 51.02 |
| 1990 | 7.65 | 4.28 | 5.10 | 2.57 | 10.82 | 4.20 | 3.00 | 1.15 | 1.38 | 3.62 | 3.14 | 4.16 | 51.07 |