Reports of explorations and surveys, to ascertain the most practicable and economical route for a railroad from the Mississippi River to the Pacific Ocean: Vol. 1, Pt. 2

GENERAL NOTES ON THIIE CLIMATE.
LETTER OF MR. L. BLODGET TO CAPTAIN A. A. HUMPHREYS, TRANSMITTING GENERAL NOTES ON
THE CLIMATE ON ROUTE NEAR THE FORTY-SEVENTH AND FORTY-NINTH PARALLELS.
WASHINGTOn, Agust 14, 1855.
DEAR SrR: The barometric and meteorological observations made in connexion with the survey
of the route near the 47th and 49th parallels, which were recently received and placed in my hands,
are scarcely sufficient for the general illustration of climate of the district traversed by the survey
which was originally designed, and under which purpose those at the permanent iosts were
instituted. The observations made by the survey at the greater altitudes, both at temporary
posts and on the several lines, are indispensable for this purpose, and further measurements are
necessary of the amount of precipitation at all altitudes. There are two valuable series, however,
at Fort Benton and at Cantonment Stevens, St. Mary's valley, of nearly a year each. These
were taken with great care, and, as they would best supply the lost journals of the survey, as
well as give positive results in regard to the climate of a new district, they appear worthy of
publication in detail. They have, therefore, been carefully prepared for that purpose, and are
followed by summaries at Fort Pierre, on the Missouri, Columbia barracks, and Olympia, and by
the journal of the survey of Lieut. Mowry, east of the Cascade mountains.
For other explanations, and for some deductions and comparisons in regard to the general
climate of the district, I beg to refer you to the general notes and remarks prefacing the tables.
Very respectfully, your obedient servant,
L. BLODGET.
Capt. A. A. HUMPHREYS,
Top. Engs., in Charge of Once of P. R. Surveys.
GENERAL NOTES ON THE CLIMATE ON THE ROUTE NEAR THE 47TH AND 49TH PARALLELS,
BY MR. LORIN BLODGET.
The number of meteorological observations made within a few years at the military posts on the
coast of the Pacific, is sufficient to have furnished a very good knowledge of that climate already,
and its more striking features are comparatively well understood. For the interior and the
mountainous districts, however, there are but few records, and none have been given to the public
from points north of the latitude of Fort Hall and west of Fort Union, on the Missouri. It was
intended to establish a sufficient number of posts on the western border of the plains, and in the
mountains and interior valley of Washington Territory, to represent every distinguishable district,
and to permit a comprehensive comparison of them. In the present result there are two or three
of these more important points embraced, but it is yet difficult to connect them in an intelligible
manner, or to show where the distinctions are. Comparisons of temperature may be made with
some accuracy from the records at hand, and these, with other obvious features, may be given in
general terms.
Fort Benton and St. Mary's valley represent the more elevated plains and valleys on each side
of the Rocky mountains, and each may be taken as decisive of the climate of a large district.
The observations in detail at these points would very well represent the itinerary of a survey
line for corresponding months for a considerable distance on either side, and they are given in full
to answer the purpose of this required knowledge of details. Between these two points there is
little of definite observation, and it is not certain how far their comparisons may be carried. It
scarcely appears whether the abrupt contrasts of the mountains of the Pacific coast exist here or
not, either in the temperature or in the amount of precipitation in rain and snow. There is not
sufficient observation aLso of the Cascade range of mountains, or of the dry plains immediately
at the east of them, especially in regard to amount of rain and snow. The journal of Lieat.
566