Arizona has five seasons: Fall, Winter, Spring, Summer, and Monsoon. Monsoon is my favorite.
By late June or early July, intense summer heat on the interior of the continent sets up a weather pattern pulling tropical moisture up from the south. After several weeks of baking at 106° with not a cloud in sight, the humidity spikes and we get afternoon storm clouds building over the mountains, the first rain in months, and a very welcome drop in daytime highs.
So this time every year I check the weather obsessively. Our lab places bets on when the monsoon is due. The average is July 3rd, but this year seems advanced and I picked June 28th. I may already have erred too cautiously, this morning feels humid and the weather service is predicting a 20% chance of rain.
Fortunately for we weather geeks, the weather service provides some great tools for monsoon watching. My favorite is the time-lapse camera that monitors cloud build-up over the Catalina mountains north of the city. The camera sits atop a building just up the street from the entomology department, and is more or less the view we get from our own building.