Stepping outside to a cold day in Colorado, unaware of the date, could very well be in Fall, Winter, or Spring. But pair that cold air with dry skin and chapped lips, you know it must be winter.
We know Colorado, in general, is dry. In terms of geography, the dry air is a result of a combination of high altitude, with no major water sources nearby (i.e. oceans, large lakes and major rivers).
High elevation and Colorado being a land-locked state has an impact on humidity year round.
But in particular, winter is the dry season here, and that's a function of weather patterns.
On average, Colorado Springs sees 0.32" of liquid equivalent precipitation in January, the lowest of any month. Pueblo's driest month is typically February, at 0.30" of precipitation.
This can be explained best by the change of seasons and how the jet streams respond.
Four to eight miles above earth's surface lies the narrow bands of strong winds called the jet stream.
Each hemisphere has two main jet streams; the cold polar jet and the warm subtropical jet.
While these are permanent features of the atmosphere, they will move with the sun. During the transition between summer and winter the jet streams move south.
By Autumn the polar jet is most active in the middle latitudes, where Colorado is situated. This brings frequent storm systems. Also during fall, the subtropical jet is still near enough to supply water vapor.
In Winter, the polar jet dives even further south. Cut off from the subtropical jet and being a land locked state, water vapor is hard to come by, especially since the dry cold air from Canada will dominate.
When we transition from Winter to Summer, the opposite happens as the jet streams move back to the north.