The climate of Montana is far more moderate and agreeable than is
generally supposed, the spring and fall months in the valleys, which
are the principal inhabited and cultivated portions, being delightfully
mild and pleasant, with frost generally only at night, though these
last till May and begin in early October.
The accompanying table shows the dates of the first and last killing
frosts at Helena, also the mean monthly temperature at Helena, which
place is chosen as a typical station, its altitude being 4,262 feet.
From this table, which extends over a period of ten years, from 1880 to
1889, inclusive, with few interruptions, it appears that the earliest
killing frost occurred on September 6th, 1881, and the latest killing
frost on May 3d, 1888, but these were very exceptional frosts, the
average dates for the same periods being September 26th and April 26th.
The maximum temperature during the same period occurred in July, 1886,
and was 103 degrees in the shade, while no other year showed a higher
temperature than 97 degrees; and the average maximum temperature for
the ten years was 94 degrees. The minimum temperature for the same
period was -40 degrees, occurring in February, 1887, while the average
minimum for ten years was -29 degrees. Great ranges of temperature are
sometimes experienced, however, especially in local areas in the higher
mountain valleys, where unusual frosts and snow flurries have occurred,
though rarely, killing potatoes and other tender crops even in July and
August.
_Monthly Mean Temperatures at Helena, Mont._
| 1880. | 1881. | 1882. | 1883.
| Mean |Killing| Mean |Killing| Mean |Killing| Mean |Killing
| Temp.|Frost. | Temp.|Frost. | Temp.|Frost. | Temp.|Frost.
---------+------+-------+------+-------+------+-------+--------------
January | | | 9.8 | | 20.0 | | 18.5 |
February | | | 25.8 | | 24.4 | | 14.1 |
March | | | 39.4 | | 31.1 | | 34.2 |
April | | | 47.6 | | 40.5 | | 40.4 |
May | | | 55.4 | | 50.4 | | 49.8 |
June | | | 61.4 | | 60.7 | | 61.8 |
July | 66.3 | | 68.3 | | 66.8 | | 67.9 |
August | 63.7 | | 66.1 | | 71.4 | | 67.2 |
September| 56.7 | | 54.6 | 6th | 60.1 | 29th | 59.2 | 20th
October | 46.3 | 22d | 37.9 | | 41.7 | | 38.9 |
November | 19.3 | | 28.8 | | 30.9 | | 33.0 |
December | 9.0 | | 30.8 | | 27.3 | | 27.4 |
Mean, | | | | | | | |
Annual | | | 43.8 | | 43.8 | | 42.7 |
---------+------+-------+------+-------+------+-------+--------------
_Monthly Mean Temperatures at Helena, Mont. (Continued)_
| 1884. | 1885. | 1886. | 1887.
| Mean |Killing| Mean |Killing| Mean |Killing| Mean |Killing
| Temp.|Frost. | Temp.|Frost. | Temp.|Frost. | Temp.|Frost.
---------+------+-------+------+-------+------+-------+--------------
January | 11.6 | | 21.0 | | 10.1 | | 20.6 |
February | 14.6 | | 28.2 | | 34.5 | | 5.0 |
March | 29.1 | | 40.6 | | 29.1 | | 40.3 |
April | 41.6 | | 45.7 | | 42.9 | | 42.4 | 20th
May | 53.9 | | 51.0 | | 54.9 | | 51.5 |
June | 62.9 | | 56.8 | | 61.1 | | 57.6 |
July | 62.5 | | 64.7 | | 69.9 | | 66.6 |
August | 66.8 | | 64.1 | | 68.1 | | 63.0 |
September| 49.7 | 6th | 55.4 | | 52.9 | 29th | 56.0 |
October | 47.0 | | 47.5 | | 43.3 | | 42.9 | 8th
November | 36.4 | | 39.1 | | 29.4 | | 33.9 |
December | 7.0 | | 31.1 | | 27.1 | | 23.0 |
Mean, | | | | | | | |
Annual | 40.3 | | 43.6 | | 43.8 | | 41.9 |
---------+------+-------+------+-------+------+-------+--------------
_Monthly Mean Temperatures at Helena, Mont. (Continued)_
| 1888. | 1889.
| Mean |Killing| Mean |Killing
| Temp.|Frost. | Temp.|Frost.
---------+------+-------+------+-------
January | 5.3 | | 16.7 |
February | 35.0 | | 25.2 |
March | 23.2 | | 39.1 |
April | 48.8 | | 49.2 |
May | 50.1 | | 53.2 |
June | 58.8 | | 63.4 |
July | 67.1 | | 66.8 |
August | 65.3 | | 67.2 |
September| 61.2 | | 55.2 |
October | 46.6 | | 50.7 |
November | 24.2 | | 31.4 |
December | 23.6 | | 22.6 |
Mean, | | | |
Annual | 42.1 | | 45.0 |
---------+------+-------+------+-------
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._
A = Ft. Assinaboine. B = Ft. Benton. C = Ft. Buford, N.D.
D = Ft. Custer. E = Ft. Keogh. F = Helena.
| A | B | C | D | E | F
----------------------+-------+------+-------+------+------+-----
Growing season of '80 | | 7.33 | 12.82 | 9.77 | 8.87 | 2.63
" " " '81 | | 7.05 | 5.81 | 3.90 | 5.67 | 7.15
" " " '82 | 4.47 | 1.29 | 5.01 | | 3.64 | 1.96
" " " '83 | 2.63 | 4.25 | 3.94 | | |
" " " '84 | 17.22 | 5.69 | 3.46 | 6.31 | | 8.09
" " " '85 | | 9.57 | 10.33 | 6.07 | | 6.29
" " " '86 | 2.52 | 2.94 | 2.65 | 5.13 | | 1.91
" " " '87 | 12.13 | | 8.00 | 2.96 | | 5.88
" " " '88 | 7.10 | | 10.16 | 8.22 | 7.28 | 4.37
" " " '89 | 5.03 | | 3.48 | 2.90 | 2.27 | 2.00
----------------------+-------+------+-------+------+------+-----
| 7.21 | 5.45 | 6.57 | 5.66 | 5.55 | 4.48
----------------------+-------+------+-------+------+------+-----
Growing season, May 15 to August 15.
_Mean Precipitation in Montana during Growing Season. (Continued)_
G = Ft. Maginnis. H = Ft. Missoula. I = Poplar River. J = Ft. Shaw.
| G | H | I | J | Average.
----------------------+-------+------+------+------+----------
Growing season of '80 | | | | | 8.28
" " " '81 | | 3.70 | | 5.78 | 5.58
" " " '82 | | 2.78 | | 4.23 | 3.00
" " " '83 | 2.27 | | 1.65 | 4.17 | 3.16
" " " '84 | 2.90 | | 5.80 | 4.30 | 6.72
" " " '85 | 5.98 | | 7.14 | 6.49 | 7.41
" " " '86 | 3.56 | | 2.67 | 2.87 | 3.03
" " " '87 | 9.47 | | 8.67 | | 7.85
" " " '88 | 10.54 | | 8.16 | | 7.98
" " " '89 | 7.47 | 1.74 | 2.23 | 1.91 | 3.23
----------------------+-------+------+------+------+----------
| 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.
----------------+-------+-------+-------+-------+-------|-------
Ft. Assinaboine | | | 12.76 | 15.10 | 25.67 |
Ft. Benton | 16.00 | 16.81 | 10.18 | 13.01 | 13.13 | 14.94
Ft. Buford, N.D.| 23.25 | 13.90 | 12.73 | 10.82 | 7.37 | 15.56
Ft. Custer | 19.65 | 11.88 | | | 16.60 | 9.34
Ft. Keogh | 15.64 | 11.44 | 10.13 | | |
Helena | | 19.94 | 10.32 | | 19.18 | 10.99
Ft. Maginnis | | | | 13.29 | 9.00 | 13.96
Ft. Missoula | | 20.56 | 13.24 | | |
Poplar River | | | | | | 10.25
Ft. Shaw | | | 14.77 | 14.21 | 12.64 | 13.64
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
----------------+-------+-------+-------+-------+-------+-------
_Annual Rain-fall in Montana, 1880-1888. (Continued)_
1886. | 1887. | 1888.
----------------+-------+-------+-------
Ft. Assinaboine | 11.48 | 18.94 | 13.99
Ft. Benton | | | 14.00
Ft. Buford, N.D.| 10.24 | 15.43 | 14.70
Ft. Custer | 13.25 | 12.18 | 14.00
Ft. Keogh | | |
Helena | 12.63 | 14.05 | 10.14
Ft. Maginnis | 15.44 | 26.00 | 25.70
Ft. Missoula | | |
Poplar River | 11.93 | 7.41 | 15.51
Ft. Shaw | 12.56 | |
Ft. Ellis | | |
Virginia City | | |
----------------+-------+-------+-------
| 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.