| Year | Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | Annual |
| 1931 | 3.63 | 5.73 | 3.52 | 3.85 | 2.96 | 0.78 | 1.99 | 6.41 | 0.22 | 2.10 | 4.17 | 9.77 | 45.13 |
| 1932 | 11.61 | 9.50 | 3.42 | 2.42 | 2.37 | 0.95 | 1.43 | 2.36 | 0.92 | 1.32 | 2.98 | 6.85 | 46.13 |
| 1933 | 1.90 | 4.32 | 5.50 | 4.09 | 5.50 | 0.60 | 12.72 | 0.60 | 1.77 | 0.73 | 0.35 | 7.40 | 45.48 |
| 1934 | 8.01 | 4.86 | 6.68 | 6.38 | 4.39 | 0.93 | 1.28 | 0.96 | 3.64 | 1.88 | 9.45 | 4.55 | 53.01 |
| 1935 | 3.03 | 2.25 | 2.37 | 7.23 | 15.60 | 2.73 | 1.61 | 0.50 | 3.44 | 2.83 | 5.65 | 5.53 | 52.77 |
| 1936 | 1.77 | 1.72 | 1.02 | 3.04 | 4.89 | 0.40 | 4.09 | 3.55 | 1.00 | 2.90 | 2.79 | 5.01 | 32.18 |
| 1937 | 7.75 | 2.70 | 3.91 | 5.11 | 1.44 | 3.89 | 3.15 | 3.34 | 2.96 | 3.65 | 4.18 | 5.13 | 47.18 |
| 1938 | 4.13 | 2.47 | 5.88 | 5.32 | 2.46 | 3.60 | 3.81 | 0.43 | 0.56 | 1.72 | 4.64 | 2.57 | 37.59 |
| 1939 | 5.62 | 6.89 | 1.86 | 2.64 | 4.20 | 1.38 | 2.88 | 0.94 | 0.58 | 2.55 | 3.84 | 9.05 | 42.43 |
| 1940 | 1.85 | 8.09 | 2.44 | 6.67 | 3.96 | 5.78 | 0.80 | 7.46 | 2.53 | 0.67 | 18.85 | 8.87 | 67.97 |
| 1941 | 2.25 | 4.95 | 3.65 | 1.61 | 6.66 | 7.69 | 7.56 | 2.46 | 5.89 | 12.79 | 3.47 | 3.70 | 62.68 |
| 1942 | 2.58 | 1.51 | 3.04 | 5.51 | 4.23 | 5.74 | 2.00 | 4.09 | 3.40 | 1.02 | 1.94 | 3.67 | 38.73 |
| 1943 | 2.94 | 1.90 | 2.15 | 0.64 | 2.46 | 1.37 | 3.89 | 2.80 | 2.03 | 2.61 | 3.73 | 4.39 | 30.37 |
| 1944 | 6.38 | 5.49 | 6.57 | 5.23 | 12.57 | 3.60 | 1.93 | 5.15 | 2.07 | 0.76 | 7.74 | 8.89 | 66.38 |
| 1945 | 5.99 | 4.68 | 4.65 | 5.69 | 4.80 | 4.11 | 6.94 | 2.51 | 4.48 | 6.74 | 1.62 | 4.46 | 56.67 |
| 1946 | 7.40 | 5.55 | 7.78 | 3.17 | 8.80 | 3.14 | 4.29 | 4.75 | 2.92 | 1.82 | 9.14 | 3.51 | 62.27 |
| 1947 | 4.45 | 2.06 | 5.07 | 4.49 | 5.96 | 3.29 | 2.28 | 0.40 | 0.80 | 1.19 | 5.08 | 5.17 | 40.24 |
| 1948 | 3.95 | 4.20 | 2.28 | 5.16 | 4.10 | 0.99 | 3.11 | 0.76 | 1.02 | 1.04 | 5.98 | 4.30 | 36.89 |
| 1949 | 7.16 | 3.37 | 4.36 | 5.05 | 5.47 | 2.47 | 3.23 | 1.40 | 3.27 | 13.24 | 0.59 | 5.57 | 55.18 |
| 1950 | 5.91 | 6.51 | 1.72 | 5.34 | 10.61 | 6.09 | 4.78 | 0.72 | 8.84 | 1.09 | 2.37 | 4.32 | 58.30 |
| 1951 | 3.84 | 3.56 | 4.31 | 1.53 | 1.40 | 3.59 | 2.77 | 0.46 | 5.45 | 0.64 | 3.06 | 6.30 | 36.91 |
| 1952 | 2.79 | 3.16 | 3.71 | 5.12 | 5.34 | 1.01 | 4.21 | 0.82 | 0.94 | 0.00 | 6.05 | 6.02 | 39.17 |
| 1953 | 3.09 | 4.14 | 7.57 | 8.71 | 11.82 | 5.41 | 6.15 | 3.21 | 1.94 | 3.05 | 3.21 | 6.02 | 64.32 |
| 1954 | 3.59 | 0.82 | 1.15 | 2.68 | 6.04 | 1.00 | 1.08 | 0.48 | 0.54 | 5.30 | 3.34 | 2.07 | 28.09 |
| 1955 | 3.80 | 4.57 | 2.02 | 3.06 | 5.95 | 0.80 | 2.07 | 5.28 | 1.47 | 2.46 | 1.25 | 2.41 | 35.14 |
| 1956 | 3.51 | 4.59 | 2.68 | 3.79 | 3.06 | 4.98 | 0.39 | 3.75 | 0.43 | 0.98 | 3.58 | 2.72 | 34.46 |
| 1957 | 5.69 | 3.99 | 5.95 | 13.96 | 6.33 | 4.40 | 3.23 | 1.35 | 6.74 | 9.97 | 9.73 | 2.93 | 74.27 |
| 1958 | 4.71 | 2.40 | 3.39 | 4.24 | 3.68 | 6.97 | 1.24 | 4.21 | 11.35 | 1.51 | 2.59 | 2.13 | 48.42 |
| 1959 | 0.87 | 4.87 | 1.84 | 5.33 | 1.79 | 3.40 | 7.71 | 3.55 | 3.77 | 3.83 | 3.11 | 6.53 | 46.60 |
| 1960 | 3.56 | 5.33 | 1.52 | 3.41 | 1.03 | 8.27 | 4.41 | 5.92 | 3.55 | 4.08 | 7.39 | 7.73 | 56.20 |