ELEVATION OF RAIN CLOUDS. 19 



This permits the escape of a part of the cloud masses which are 

 driven into the Clearwater valley, over into the St. Mary valley. They 

 then follow the course of the valley northward until the northern end 

 of the Elk range of mountains is reached. This range is simply the 

 dividing ridge between the most western of the St. Joseph forks and 

 the St. Mary basin. At the northern end of this range lies a broad 

 plateau which extends from the St. Mary River to the St. Joseph. The 

 air currents pass over this plateau eastward, and reaching the St. 

 Joseph valley are again deflected northward to join the air masses 

 traveling into the valley of the Cceur d'Alene. 



The height at which the rain clouds travel varies with the season. 

 The rainy season in the middle of June and the earliest rains in 

 September usually begin from clouds floating considerably higher than 

 2,100 meters (7,000 feet) above sea level. After the rain has been falling 

 for a few days the clouds go much lower, but seldom under the 1,300- 

 meter (4,300 foot) line. These altitudes are known partly from obser- 

 vations of the height at which the lower or earth surface of the rain 

 clouds travel in their course along and over mountain ridges and crests 

 with known elevations and partly from ascensions of various peaks 

 that have been made while rain and snow storms were in progress, the 

 altitude having been ascertained by means of aneroids. 



During the December precipitation the clouds float at their lowest 

 elevation, which seldom falls below 800 meters (2,600 feet). The 

 velocity of the wind during the storm where free and unobstructed 

 traverse exists, as on the summit of the highest elevations, is subject 

 to great variations, but is probably seldom less than 40 kilometers 

 (25 miles) an hour. In the early part of the month of September when 

 I visited the high ridges to the south of Wiessner Peak during the 

 prevalence of one of the early storms of the season, the wind, coming 

 from the southwest, reached at times a velocity of 05 kilometers (50 

 miles) an hour. This was on the summit of ridges having an elevation 

 of about 2,100 meters (7,000 feet) and unobstructed by trees or higher 

 mountains in the neighborhood. The temperature during the storm, 

 which lasted three days, remained at 9° C. (48.2° F.), and the lower 

 limit of the nimbus was about 1,500 meters (4,800 feet). 



The peculiar circumstance was noted in connection with the rain 

 cloud that the side toward the earth was in a continual state of rising 

 and falling. The space through which this took place was about 220 

 meters (700 feet) in height. The barometer was not affected, but the 

 character of the rain that was falling varied considerably. When 1 

 was thoroughly enveloped in the nimbus but little of the contained 

 moisture fell as rain, but from the branches of every tree or upright 

 object the water, condensing from the rain fog, was pouring in streams. 

 Whenever the cloud lifted the rain fell in torrents. 



Most of the severe storms begin with electrical disturbances. There 

 are passing showers, accompanied by thunder and lightning which 

 soon cease, and the storm proper begins. Local showers of short 



