On September 5th of this year in the upper Madison Valley above 6500 feet of elevation, a temperature was experienced in the forenoon of 70 degrees, while at about 8 o'clock on the same evening, a snow squall occurred during which the thermometer must have fallen several degrees below the freezing point; by 9 o'clock on the following morning all of the snow had disappeared and the temperature had greatly moderated.
The summer months in these mountain valleys are always agreeably warm during the day time, while the nights are cool and pleasant. In the winter the climate is very cold, though not so uncomfortable as the temperature would indicate, owing to the dryness of the atmosphere and the absence of very high winds in the mountain valleys. The more exposed plains to the north are subject to the frequent and agreeable visits of the famous "Chinook" winds, which blow from the west, and under whose influence heavy falls of snow disappear in a single day.
The following table shows the mean annual rain-fall at various Signal Service stations in Montana, and from these it will be seen that during a period of ten years the maximum rain-fall for the entire State has only been 20.33 inches in 1880, while the minimum has occurred during 1886 and was but 12.52 inches; the average precipitation for this period was 15.25 inches.
Mean Precipitation in Montana during Growing Season.
| Growing season of | Ft. Assina- boine. | Ft. Benton. | Ft. Buford, N.D. | Ft. Custer. | Ft. Keogh. | Helena. | Ft. Maginnis. | Ft. Missoula. | Poplar River. | Ft. Shaw. | Average. |
| 1880 | 7.33 | 12.82 | 9.77 | 8.87 | 2.63 | 8.28 | |||||
| 1881 | 7.05 | 5.81 | 3.90 | 5.67 | 7.15 | 3.70 | 5.78 | 5.58 | |||
| 1882 | 4.47 | 1.29 | 5.01 | 3.64 | 1.96 | 2.78 | 4.23 | 3.00 | |||
| 1883 | 2.63 | 4.25 | 3.94 | 2.27 | 1.65 | 4.17 | 3.16 | ||||
| 1884 | 17.22 | 5.69 | 3.46 | 6.31 | 8.09 | 2.90 | 5.80 | 4.30 | 6.72 | ||
| 1885 | 9.57 | 10.33 | 6.07 | 6.29 | 5.98 | 7.14 | 6.49 | 7.41 | |||
| 1886 | 2.52 | 2.94 | 2.65 | 5.13 | 1.91 | 3.56 | 2.67 | 2.87 | 3.03 | ||
| 1887 | 12.13 | 8.00 | 2.96 | 5.88 | 9.47 | 8.67 | 7.85 | ||||
| 1888 | 7.10 | 10.16 | 8.22 | 7.28 | 4.37 | 10.54 | 8.16 | 7.98 | |||
| 1889 | 5.03 | 3.48 | 2.90 | 2.27 | 2.00 | 7.47 | 1.74 | 2.23 | 1.91 | 3.23 | |
| 7.21 | 5.45 | 6.57 | 5.66 | 5.55 | 4.48 | 6.03 | 2.74 | 5.19 | 4.25 | 5.23 | |
| Growing season, May 15 to August 15. | |||||||||||
Annual Rain-fall in Montana, 1880–1888.
| 1880. | 1881. | 1882. | 1883. | 1884. | 1885. | 1886. | 1887. | 1888. | |
| Ft. Assinaboine | 12.76 | 15.10 | 25.67 | 11.48 | 18.94 | 13.99 | |||
| Ft. Benton | 16.00 | 16.81 | 10.18 | 13.01 | 13.13 | 14.94 | 14.00 | ||
| Ft. Buford, N. D. | 23.25 | 13.90 | 12.73 | 10.82 | 7.37 | 15.56 | 10.24 | 15.43 | 14.70 |
| Ft. Custer | 19.65 | 11.88 | 16.60 | 9.34 | 13.25 | 12.18 | 14.00 | ||
| Ft. Keogh | 15.64 | 11.44 | 10.13 | ||||||
| Helena | 19.94 | 10.32 | 19.18 | 10.99 | 12.63 | 14.05 | 10.14 | ||
| Ft. Maginnis | 13.29 | 9.00 | 13.96 | 15.44 | 26.00 | 25.70 | |||
| Ft. Missoula | 20.56 | 13.24 | |||||||
| Poplar River | 10.25 | 11.93 | 7.41 | 15.51 | |||||
| Ft. Shaw | 14.77 | 14.21 | 12.64 | 13.64 | 12.56 | ||||
| Ft. Ellis | 30.16 | 17.55 | 19.28 | 15.72 | 22.02 | 32.63 | |||
| Virginia City | 17.29 | ||||||||
| 20.30 | 16.01 | 12.93 | 13.69 | 15.73 | 15.41 | 12.79 | 15.67 | 15.45 | |
Moreover, from the first table, showing the average monthly precipitation at the Helena station, it will be seen that but 4.48 inches fall during May 15th to August 15th, inclusive, which is the growing season when the crops require moisture.
The information regarding evaporation is as yet very meagre, but from four stations observed in different parts of the State during August, September and October, it appears that the total average evaporation for the three months was 18 inches, and from the best information obtainable it appears that the total annual evaporation is 36 inches, that is to say, the surface of the water in a lake or reservoir will be lowered by evaporation 3 feet in a year.
WHY MONTANA IS AN ARID COUNTRY.