Source: Eazydp under Public Domain Dedication / Wikimedia Commons
21. Tubular clouds
Tubular clouds, a type of arcus cloud also known as roll cloud, form low and horizontally in the sky. They tend to form along the edges or in the downdrafts of thunderstorms. While relatively rare and ominous-looking, these clouds are not usually a sign of dangerous weather.
Source: David McNew / Getty Images
22. Fire whirl
Fire whirls, also known as fire tornadoes, are a bizarre and frightening weather phenomenon sometimes encountered by those fighting wildfires. These rare events are created from the high heats in large fires. Fire whirls are relatively uncommon with just a handful of officially documented instances in the last few decades.
