Having lived in New England most of my life, I’m not used to seeing rainstorms approaching from miles off, but it turns out this is a pretty common sight out in the wide-open West. I took this picture two weeks ago in Arizona. At the time it was the tail end of the monsoon season in the southwest and there were thunderstorms almost every afternoon. I took the picture near the summit of Mt. Lemmon, a 9,000-foot peak just north of Tucson in the Catalina mountains. It was a perfectly sunny day, until we drove into a wall of rain three quarters of the way up the mountain. The rain clouds eventually rolled off the top of the mountain, and on the way down we pulled over at an overlook just in time to snap a picture of a column of rain retreating over the foothills.