I've Been Thunderstruck

A couple days ago, as a storm was moving out of the area, we got some classic cirrus clouds in the upper atmosphere. These types of clouds are very high in the atmosphere, are traditionally thin with wispy strands, and can often herald the arrival of a storm (in this case they were remnants of a previous storm). Cirrus clouds like to live at levels above 26,000 feet (8000 meters), and are formed when water vapor freezes into ice crystals. The lack of moisture at such high altitudes is one of the reasons these clouds tend to present so thin and wispy.

Cirrus Clouds in Tucson, AZ

A lot of times in Tucson we see hair like filaments of ice crystals precipitating out of the clouds in the form of what’s called virga. These streaks often indicate the difference in the motion of air between the upper part of the cirrus cloud and the lower air below it. It appears as though rain is coming from the cloud, but it’s actually ice crystals, most of which evaporates before it hits the ground (especially in Arizona). On some days, cirrus cloud development is so extensive that they become virtually indistinguishable from one another, forming what’s called cirrostratus clouds.

Another type of cirrus cloud that you’re already very familiar with is the condensation trails, or contrails,  seen in the sky coming from planes. These trails are basically artificial clouds formed by the exhaust of aircraft engines. As the hot exhaust gases cool in the surrounding air they may precipitate a cloud of microscopic water droplets. If the air is cold enough, this trail will comprise tiny ice crystals. On some days, with a high level of air traffic, you can see contrails crisscrossing the sky, and these contrails often hang around for some time. It’s pretty neat!

Clouds are very cool, and an obviously integral part of weather. I intend to eventually go through all the various cloud types, hopefully using images I’ve shot with my camera. If you understand why a particular cloud type is in the area, you have a good idea of what sort of weather might be on the way.