Table VII (a).[2]
| Groups of stations. | Mean latitude of group. | Total years of record. | Percentage of annual rainfall. | ||||
|---|---|---|---|---|---|---|---|
| ° ´ | Spring. | Summer. | Autumn. | Winter. | Spring and Summer. | ||
| Eight stations in Dakota, Minnesota, and Nebraska | 45 20 | 67 | 29 | 43 | 19 | 9 | 72 |
| Three stations in Kansas | 38 45 | 38 | 24 | 41 | 24 | 11 | 65 |
| Eight stations in Texas | 29 45 | 85 | 19 | 36 | 31 | 14 | 55 |
[2] In computing the several means of [Table VII] (a) from the seasonal means of [Table VII], the latter were weighted according to the lengths of the records by which they had been obtained.
A moment’s inspection will show that the middle group is intermediate between the northern and southern in all its characters. The spring quota of rainfall progressively diminishes from north to south, and so does the summer, while the fall and winter quotas increase. What is lost in summer is gained in winter, and thereby the inequality of rainfall from season to season is diminished, so that a rainy season is not so well defined in Texas as in Dakota. What is lost in spring is gained in autumn, and thereby the place of the rainy season in the year is shifted. In Dakota the maximum of rain is earlier than in Texas, and corresponds more nearly with the maximum of temperature.
Table VIII.—Seasonal precipitation in the San Francisco Region.
| Station. | Extent of record. | Mean annual rainfall. | Percentage of annual rainfall. | ||||
|---|---|---|---|---|---|---|---|
| Y. M. | Inches. | Spring. | Summer. | Autumn. | Winter. | Winter and spring. | |
| Alcatraz Island | 9 5 | 16.49 | 16 | 0 | 11 | 73 | 89 |
| Angel Island | 5 11 | 18.58 | 19 | 0 | 15 | 66 | 85 |
| Benicia Barracks | 18 3 | 14.90 | 28 | 1 | 15 | 56 | 84 |
| Fort Miller | 6 9 | 19.00 | 38 | 0 | 16 | 46 | 84 |
| Fort Point | 14 11 | 17.36 | 21 | 0 | 13 | 66 | 87 |
| Monterey | 12 3 | 15.71 | 28 | 2 | 14 | 56 | 84 |
| Sacramento | 18 3 | 19.24 | 29 | 1 | 14 | 56 | 85 |
| San Francisco; Presidio | 20 2 | 20.29 | 24 | 2 | 13 | 61 | 85 |
| San Francisco | 24 4 | 21.49 | 24 | 1 | 14 | 61 | 85 |
| Weighted means | — | — | 25 | 1 | 14 | 60 | 85 |
Total extent of record = 130 years.
Mean of yearly rainfalls = 15.90.
Second District.—In the San Francisco Region a rainy season is still more definitely marked, but occurs at a different time of year. It will be seen by [Tables III] and [VIII] that no rain falls in summer, while the winter months receive 60 per cent. of the annual precipitation, and the spring 25 per cent. The general yearly rainfall of the district is only about 16 inches, but by this remarkable concentration a period of five months is made to receive 13 inches. The winter temperature of the district is no less remarkable, and supplies the remaining condition essential to agriculture. Frosts are rare, and in the valleys all the precipitation has the form of rain. The nine stations which afford the rainfall records given above show a mean spring temperature of 57° (see [Table IX]). Thirteen inches of rain coming in a frostless winter and spring have been found sufficient for remunerative agriculture.
Table IX.—Mean temperatures, by seasons, for the San Francisco Region.
| Station. | Extent of record. | Mean temperatures, in degrees Fahr. | ||||
|---|---|---|---|---|---|---|
| Y. M. | Spring. | Summer. | Autumn. | Winter. | Year. | |
| Alcatraz Island | 8 6 | 55 | 57 | 60 | 54 | 57 |
| Angel Island | 3 1 | 58 | 63 | 61 | 52 | 58 |
| Benicia Barracks | 15 7 | 58 | 67 | 62 | 49 | 59 |
| Fort Miller | 7 6 | 64 | 86 | 67 | 49 | 67 |
| Fort Point | 10 11 | 55 | 59 | 58 | 52 | 56 |
| Monterey | 12 5 | 55 | 60 | 57 | 50 | 55 |
| Sacramento | 14 0 | 59 | 71 | 62 | 48 | 60 |
| San Francisco; Presidio | 19 0 | 54 | 57 | 57 | 50 | 55 |
| San Francisco | 11 2 | 55 | 58 | 58 | 50 | 55 |
| Means | — | 57 | 64 | 60 | 50 | 58 |