Atmospheric Visibility, or "Where did the mountains go?"

A good question from Carrie,
"I'd like to know why you can see the mountains to the south (like the Spanish Peaks) only on certain days. It seems like the best times to see them are on cold, partly cloudy days in winter. I'm really curious as to the science pertaining to this!"
And the answer is...
How well you can see the mountains depends on a number of factors that affect the visibility, such as dust and haze…but the situation you describe, “partly cloudy [or clear] winter days” is all about the amount of water in the air. When it’s colder, there’s usually less moisture = better visibility. Good job on spotting the key!