﻿SUA IV — THE SELKIRKS 



48l 



in the midst of the subalpine zone. 2 From these records it is 

 evident that less daily variation occurs at high altitudes. The 

 daily maxima are notably less than those at lower altitudes, the 

 nightly minima only slightly so. This accords well with the general 

 observations of meteorologists. 



From records kept at Revelstoke throughout the year, it is 

 possible to gain some idea of the temperature during the winter. 

 The minimum of — 50 0 C, while striking, is probably without sig- 

 nificance for vegetation. At higher altitudes, owing to inversion 

 of temperature, the cold is probably much less severe. A regis- 

 tering thermometer was left over the winter of 1908- 1909 on the 

 top of Mount Grizzly (3000 m.). When found the following 

 summer, it had every appearance of being in good working order and 

 the recorded minimum was — i°F. Of course, the rocks where 

 the instrument was secured were deeply covered with snow during 

 most of the year. 



Occasional frosts occur even at river level in midsummer. Thus, 

 on the night of July 20, 1905, there was a heavy frost in the valley of 

 Goldstream (616 m.). I was unable to learn whether there was 

 frost on the mountain flanks a little higher up or not, but suspect 

 that the low temperature prevailed only in the floor of the valley 

 (a case of temperature inversion). 



At and above timber line snow may fall at any season. Each 

 summer there are usually one or two storms in which "new snow" 

 covers the mountains from timber line upward — quite the same 

 phenomenon that is seen in the Alps. Aside from such storms and 

 away from the immediate vicinity of the glaciers, nightly frosts are 

 mostly light and irregular during July and the early part of August 

 (light frost in the alpine meadows is often visible when the ther- 

 mometer has failed to record freezing). After the middle of August 

 the nights become notably cooler, the nightly frosts become sharper, 

 and by the middle of September they are frequent at all altitudes. 



Precipitation.— The volume of precipitation appears to in- 

 crease from the southeast to the northwest. In the terraced portion 

 of the Columbia Valley, where there are a number of ranches, sum- 

 mer rainfall is so far from that desirable for crops that irrigation 



2 These records are unhappily lost. 



