People have done good explanations of why the colder air is "more clear," but you can also check with your friendly neighborhood amateur astronomer, who will tell you that cold, dry nights are the clearest for stargazing. And that, sadly for us stargazers, the best nights for stars are often the ones where your fingers get too cold to operate the scope. :)

Where I live, when it's around 20-35*, there's always a lot of moisture in the air, and it's usually cloudy. When it's cold, crisp, and clear as a bell, it's usually below 10 degrees; the conditions are AMAZING for stargazing, but my poor fingers freeze within half an hour.

Clear Dark Sky is a Canadian government forecast service that gives a stargazing forecast for North America .. they give good and clear explanations on atmospheric transparency and "seeing." I expect if you peek at the astronomy forecast,you will find your view of the mountains is the most crisp on days when transparency is high. https://www.cleardarksky.com/c/Ottawakey.html