Some cloud formations can look scary, and they can be a sign of a storm. Here's how they form and what they are.

A long, tubular cloud that appears to roll about a horizontal axis. Often forms along the leading edge of a storm front or gust front. Indicates a change in wind direction and can precede severe ...

So what are mammatus clouds? And what do they signal is coming? Mammatus clouds often form on the base of storm clouds but can be associated with other types of clouds as well. NOAA describes them ...

The clouds, which often form in turbulent air, can stretch for hundreds of miles and can be a sign of a gathering storm. For the clouds to form, there must be a sharp change in temperature.