Colorado Climatology 
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the State a long succession of relative!}^ warm and bright 
sunshiny days. During the summer months a low pressure 
is prevalent over the Salt Lake region, causing little precipita 
tion, but this area of low pressure causes easterly winds east 
of the mountains and the air which is drawn up the slopes of 
the mountains becomes chilled by the elevation and causes 
precipitation during the warmer half of the year. 
Though distant, the influence of the Gulf of Mexico is felt 
to a varying extent. During the summer months when there 
is a general stagnation in the movement of the northern low 
pressure areas, sufficient time is afforded for moisture to be 
brought to the eastern slope, which causes increased precipi¬ 
tation east of the mountains during the warmer half of the 
year. The difference in the temperature of the two slopes is 
quite marked in the winter months, when cold waves from 
north of Montana sweep southward along the eastern slope of 
the Rocky Mountains, but do not pass to the western slope, as 
the continental divide is an effective barrier. In the areas of 
high pressure or anti-cyclones, the greatest cold is generally 
confined to the lower stratum of air whose upper limit does 
not always reach as high as the mountain tops. As a matter 
of fact during these periods of low temperatures the adjacent 
high altitude stations experience relatively moderate tempera¬ 
tures, which condition, if not already in existence in the west¬ 
ern valley, is soon in evidence. Cold waves are the result of 
the transferring of cold air from the north, often increased 
by the radiation in the clear dry air. 
EFFECT OF CONTINENTAL DIV IDE 
The continental divide is also effective in moderating the 
winter temperatures of the eastern slope. When the distribu¬ 
tion of the pressure is favorable to westerly winds, remarkable 
rises of temperature occur. These are called ^ ^ chinook ’ ’ winds. 
That the ‘ ^ chinook ’ or warm winds, blowing from the snow- 
covered mountains should be so warm and dry is explained by 
the fact that the air as it is forced up the western slope, owing 
to the high elevation, is unable to hold the moisture it contains 
and precipitation occurs. Its latent heat is liberated, so that 
the air reaches the top of the mountains colder but relatively 
warmer than when it began its ascent, and when in descending 
it is compressed, it reaches us as a warm dry wind. Its effect 
in evaporating the snow on the plains has been the salvation of 
many herds of stock that must otherwise have perished. Lo¬ 
cally these winds are accompanied by a low barometer, and 
soon a long wind cloud is seen like a banner lying close to the 
