Cloudy and Cool

We’ve all heard of cumulus clouds even if we don’t know all of its variations, such as altocumulus, cumulonimbus, and, my personal favorite, cotton ball.

Fine–I’ll admit it. I made that last one up, but cumulus clouds range from the fluffy white cloud that changes shape as it drifts by while you lie on your back on a warm summer day to a 10-mile tall towering cloud that produces a life-changing tornado.

Cumulus clouds are all formed when warm air (or hot air) near the ground contrasts with cool air (or cold air) higher in the atmosphere and there is enough moisture  present, but it’s not always a purely atmospheric process. Other natural or man-made events can aid in the production of cumulus clouds, most notably fire.

Fire Cloud–Pyrocumulus

Fires, man-made or natural, can sometimes add enough heat to the warm-air-near-the-ground part of the equation to result in a cloud when there otherwise would not be one. Many times, it’s just an interesting but innocent small cloud, such as the example in the recent blog Pyrocumulus in northern Shelby Co. (from my blog friend Erik Proseus at MemphisWeather.Net Blog).

At other times, it can create a full-blown thunderstorm. This is a rare event and is more likely to occur in Alaska than in other areas. Fires are often huge in Alaska, producing tremendous amounts of heat, and upper-level temperatures are chillier in Alaska than in areas farther to the south. Therefore, when enough moisture is present, a fire can lead to a rain-producing thunderstorm.

–Paul Yeager