CHINOOK. A term applied by the early settlers of the Northwest Territory and in me teorological literature to a strong warm and dry south or west wind descending the eastern slopes of the Rocky Mountains into Montana and Wyo ming, evaporating or melting the snow and bring ing great relief in cold weather. The name was probably given to it because the wind occurred in, or blew from, the territory occupied by the Chinook Indians. It was at first supposed by the settlers to he a branch of the warm south west wind of the Pacific Ocean that had •ros,ed over the Rocky Mountain range: indeed. the moist southwest winds on the coasts of Oregon and Washington have also been called chinook winds. It is a mistake to think that the Montana chinook originates over the warm waters of the Pacific.; it is essentially a descending wind and owes its temperature and dryness to this fact; it belongs to the same class as the Filhu winds of Switzerland. Several very different combinations of conditions may cause descending winds, but in any case descending air by coining under greater pressure must be compressed and therefore warmed up at the rate of about 1° Fahrenheit for each 183 feet of I , or 1° Centigrade per 100 meters. Therefore a fall of 5500 feet, such
as is very common in Bowing over the Bockies, will raise the temperature of the air by 30' Fahr enheit, and as this warmth is very slowly lost, the warm air spreads over a wide extent of ground. The hot winds of Kansas and Iowa un doubtedly also owe their high temperatures to the fact that the air is descending rapidly. As nu moisture is added to the mass of descending air, the Falin winds of Switzerland, the chinooks of Montana. and especially the hot winds of Kansas are extremely dry, and evaporate and absorb any snow or moisture at the surface of the ground. The proper explanation of chinooks was first given by G. Al. Dawson, 1879-1880, but the most important early paper on the subject was by Alark Harrington of the University of Michigan, in the .1 merican Meteoro logical Journal, Vol. 111. (Ann Arbor, 1887).