Cumulus clouds are often thought of as fair-weather clouds, and they usually are—but they can grow into something far more ominous. Cumulus clouds look like big balls of white or light gray cotton drifting across the sky, usually have a flat base, and don’t generate much precipitation in their young, puffy phase. They most often form when the morning Sun heats up the earth’s surface and fills the sky with hundreds of popcornlike clouds floating serenely over your head.
