Background Information 



The four stations selected for observing variations in mountain grassland weather 

 were near the north end of the Gravelly Range, Madison County, in southwestern Montana. 

 The Gravelly Range of mountains has a generally rounded crest and a number of points 

 extending above 9,000 feet in elevation. Its north-south axis is approximately 30 

 miles long. Toward the west, the Ruby River separates the Gravelly Range from the 

 equally high north-south Snowcrest Range. Toward the east, the Madison River separates 

 the Gravelly Range from the Madison Range, which has numerous peaks rising well over 

 10,000 feet. 



Two stations were placed on facing slopes (lat. 45°09' N. , long. 111°48' W.) at an 

 elevation of 7,100 feet on the east flank of the Gravelly Range. One was on a gently 

 sloping southwest exposure; the other, 200 yards southwest of the first, was on a 

 gently sloping northeast exposure. Two more stations straddled the crest (lat. 45°07' 

 N., long. 111°52' W.) of the Gravelly Range at an elevation of 8,200 feet. One was on 

 a gently sloping northeast exposure on the east side of the crest; the other, approx- 

 imately 700 yards southwest of the first, was on a gently sloping southwest exposure 

 on the west side of the crest. The upper stations were approximately 5 miles south- 

 west of the two lower ones. 



All four stations were on natural mountain grasslands where the vegetation, a 

 mixture of low-growing grasses and f orbs , seldom exceeds 12 inches in height. 

 Generally, Idaho fescue {Festuoa idahoensis) is the dominant species. Occasional 

 patches of sagebrush {Artemisia tridentatd) occur on the deeper soils. The grasslands 

 at the lower elevation are interspersed with stands of Douglas-fir {Pseudotsuga 

 menziesii) and limber pine {Finus flexilis) . Grasslands at the upper elevation are 

 interspersed with stands of limber pine, lodgepole pine {Finns oontorta) , and subalpine 

 fir {Abies lasiooarpa) . Nowhere were trees closer than about 100 yards to the weather 

 stations , 



Instrumentation 



All four stations were equipped with similar weather-measuring instruments; two 

 exceptions will be mentioned later. All equipment was placed within a 20- by 40-foot, 

 four-strand barbed wire enclosure. 



Air temperature and relative humidity were recorded continuously by a 7-day 

 hygrothermograph , installed 4-1/2 feet above the ground in a standard Weather Bureau 

 instrument shelter. 



Soil surface temperatures were measured continuously by a 7-day thermograph. The 

 sensor bulbs of the thermograph were 1/2- by 8-inch lead-covered cylinders attached to 

 mercury-filled Bordon mechanisms by 10-foot steel capillary tubes. One sensor was 

 placed in a permanent position on the soil surface in perpetual shade, another, in the 

 sun. The shaded sensor was beneath a well-ventilated, double-slatted aluminum shade. 

 The shade was about 5 inches above the sensor bulb and completely sheltered it from 

 direct sunlight. The sensor fully exposed to the sun was placed on a cultivated soil 

 surface that was free of vegetation. The bulb of this sensor was lightly coated with 

 soil particles to give its surface the color and texture of soil. 



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