| Year | Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | Annual |
| 1931 | 1.30 | 1.17 | 1.10 | 1.95 | 1.00 | 0.40 | 0.70 | 1.70 | 0.22 | 1.66 | 0.81 | 1.90 | 1.95 |
| 1932 | 3.36 | 4.15 | 1.85 | 1.46 | 1.80 | 0.51 | 0.90 | 1.06 | 0.30 | 0.91 | 1.88 | 1.45 | 3.36 |
| 1933 | 1.15 | 1.52 | 1.90 | 1.14 | 2.40 | 0.35 | 8.20 | 0.24 | 1.06 | 0.44 | 0.21 | 2.90 | 2.90 |
| 1934 | 2.14 | 1.72 | 2.55 | 2.72 | 1.53 | 0.93 | 0.42 | 0.47 | 0.97 | 1.82 | 4.50 | 1.52 | 4.50 |
| 1935 | 1.65 | 0.69 | 1.39 | 2.20 | 7.48 | 0.78 | 0.42 | 0.23 | 2.13 | 1.91 | 2.02 | 4.57 | 4.57 |
| 1936 | 1.09 | 0.46 | 0.27 | 0.94 | 1.85 | 0.38 | 1.80 | 2.17 | 0.40 | 1.14 | 0.97 | 2.29 | 2.29 |
| 1937 | 1.45 | 1.18 | 0.71 | 1.76 | 1.35 | 1.31 | 1.63 | 1.21 | 1.00 | 1.69 | 1.73 | 2.15 | 2.15 |
| 1938 | 1.46 | 1.47 | 2.23 | 2.42 | 1.31 | 2.45 | 2.31 | 0.16 | 0.35 | 0.80 | 2.53 | 0.88 | 2.53 |
| 1939 | 1.13 | 1.04 | 1.55 | 1.51 | 1.45 | 0.60 | 1.83 | 0.21 | 0.28 | 1.59 | 1.34 | 5.90 | 5.90 |
| 1940 | 0.71 | 2.40 | 1.31 | 2.22 | 3.02 | 2.93 | 0.39 | 2.82 | 2.33 | 0.29 | 8.85 | 2.78 | 3.02 |
| 1941 | 0.93 | 2.81 | 1.47 | 0.56 | 1.97 | 2.46 | 2.19 | 0.71 | 2.60 | 9.13 | 1.73 | 1.02 | 2.81 |
| 1942 | 1.27 | 0.66 | 0.83 | 2.06 | 1.79 | 1.12 | 0.87 | 2.23 | 2.64 | 0.41 | 1.10 | 2.15 | 2.64 |
| 1943 | 1.32 | 1.33 | 0.96 | 0.33 | 0.61 | 0.43 | 1.00 | 2.08 | 0.43 | 1.46 | 1.58 | 1.21 | 2.08 |
| 1944 | 1.20 | 1.27 | 2.29 | 2.16 | 2.97 | 2.14 | 0.79 | 3.32 | 1.47 | 0.75 | 2.21 | 1.92 | 3.32 |
| 1945 | 1.88 | 1.59 | 1.04 | 2.73 | 1.94 | 1.67 | 1.88 | 1.15 | 1.76 | 2.08 | 1.17 | 1.67 | 2.73 |
| 1946 | 2.28 | 1.35 | 2.90 | 1.31 | 3.23 | 1.64 | 2.00 | 1.52 | 1.41 | 0.60 | 2.23 | 0.97 | 2.28 |
| 1947 | 0.95 | 0.83 | 1.92 | 1.79 | 2.89 | 1.58 | 1.81 | 0.24 | 0.57 | 0.96 | 1.30 | 2.36 | 2.36 |
| 1948 | 0.64 | 1.53 | 1.05 | 2.62 | 1.42 | 0.75 | 1.38 | 0.25 | 0.58 | 0.62 | 2.15 | 2.58 | 2.58 |
| 1949 | 2.64 | 0.74 | 1.57 | 1.38 | 4.28 | 1.67 | 0.92 | 0.85 | 1.23 | 3.83 | 0.59 | 0.97 | 3.38 |
| 1950 | 1.73 | 2.39 | 0.52 | 2.20 | 3.55 | 2.00 | 1.28 | 0.47 | 3.92 | 0.91 | 2.05 | 4.00 | 4.00 |
| 1951 | 2.04 | 1.34 | 1.71 | 0.55 | 1.00 | 1.64 | 2.12 | 0.20 | 2.90 | 0.23 | 1.23 | 2.39 | 2.39 |
| 1952 | 1.77 | 0.72 | 1.49 | 1.99 | 2.53 | 0.40 | 1.27 | 0.81 | 0.75 | 0.00 | 3.18 | 2.66 | 3.18 |
| 1953 | 2.23 | 1.06 | 2.59 | 5.90 | 3.72 | 2.93 | 3.16 | 1.60 | 1.86 | 3.05 | 1.23 | 2.53 | 5.90 |
| 1954 | 1.02 | 0.64 | 0.45 | 1.02 | 2.02 | 0.52 | 0.48 | 0.23 | 0.35 | 2.89 | 1.87 | 1.40 | 2.89 |
| 1955 | 1.16 | 1.62 | 0.80 | 1.50 | 2.74 | 0.42 | 0.92 | 2.00 | 0.56 | 1.65 | 0.81 | 1.04 | 2.74 |
| 1956 | 1.93 | 1.90 | 0.70 | 2.44 | 1.24 | 2.78 | 0.39 | 2.01 | 0.43 | 0.30 | 1.35 | 0.72 | 2.78 |
| 1957 | 1.60 | 1.20 | 1.40 | 3.90 | 1.54 | 0.85 | 1.52 | 0.83 | 2.00 | 4.10 | 2.17 | 1.31 | 4.10 |
| 1958 | 1.86 | 0.88 | 1.10 | 1.36 | 1.75 | 3.33 | 0.86 | 1.99 | 4.83 | 0.58 | 0.80 | 0.90 | 4.83 |
| 1959 | 0.40 | 1.77 | 0.53 | 1.44 | 0.97 | 0.93 | 4.60 | 1.70 | 1.76 | 1.93 | 2.00 | 2.73 | 4.60 |
| 1960 | 1.12 | 1.17 | 1.07 | 1.92 | 0.73 | 1.78 | 1.45 | 1.75 | 2.28 | 1.04 | 2.17 | 1.58 | 2.28 |