Have you ever seen mammatus clouds? They look like pillows of clouds hanging down from the undersides of thunderstorm anvils. Especially noticeable at sunset or any time when there is a low sun angle, but they can occur any time. Some of my friends reported seeing some yesterday with some thunderstorms that passed through Atlanta. Normally they are associated with cold air flowing out of the anvils and usually only occur in the strongest thunderstorms, whether or not they have severe weather. You can read more about the science of mammatus clouds at https://site.extension.uga.edu/climate/2016/06/the-science-of-mammatus-clouds/ and see some spectacular photos from EarthSky at https://earthsky.org/earth/amazing-photos-of-mammatus-clouds.

Source: Zachary Houri, Commons Wikimedia