depends very largely upon the general movements of the air; but no one can fail to realize the importance of a hot blast, a blizzard, a tornado or a sand storm—or, indeed, of any occasional storm wind that may injure growing crops and destroy property.
Along coasts, the sea breeze and the alternating land breeze are the rule rather than the exception during a considerable part of the year. As a rule, the sea breeze extends rarely higher than 3000 feet. At such times it may be merely a crosswind, and the clouds at a height of a mile may be moving in an opposite direction. The succeeding land breeze which sets in is apt to be a much stronger wind.
Mountain Valley Winds are common in all mountain regions. During the day, when the air is growing warmer, the wind blows up the valley; at night, when it is losing its heat the flow is down the valley. In narrow canyons, the night winds may be very strong—a force of 6 to 7 of the Beaufort scale.
The Chinook, one of the most important local winds, derives its name from the jargon of a tribe of Indians living near the mouth of the Columbia River. According to tradition the name means “snow-eater,” from the fact that, with its appearance, the snow begins to melt first from the higher parts of the mountain slopes and, last of all, from flood plains and valley floors.
The Chinook was made known first by early settlers in Oregon. In time it was found to exist throughout much of the montane part of the northwest. The Chinook begins as a moist wind on the windward side of a high range. As it is pushed upward along the mountain slope it is chilled by expansion below the dew-point, and condensation takes place. This liberates a great deal of latent heat, materially warming the air. The air is warmed still further by compression as it rolls down the leeward slope of the range.
In Montana, Idaho and Alberta, the Chinook wind is far-reaching in its climatic effects. Both grazing and wheat-growing are made possible in regions that otherwise would be unproductive. The Chinook wind does not differ from the Foehn wind of Europe with which it is classed. In each case moist air drawn into a cyclone and pushed over a range, descends on the other side as a warm, dry wind.
The Hot Winds of the Plains, including the Summer Winds
