Why Do Squalls Hit So Suddenly?

Evening showers, or squalls, come from cumulonimbus clouds. That kind of cloud moves across the sky very quickly. One minute it may look clear, and the next moment the clouds have moved in. That's why evening showers come down on us so suddenly. Light showers that strike suddenly on summer evenings are from cumulonimbus clouds. These summer showers, which are often accompanied by thunder and bolts of lightning, stop as quickly as they start. The clouds usually called rain clouds are nimbostratus clouds. They come in close to the ground and spread darkness as they cover the entire sky. The cumulonimbus clouds often move as fast as a car. They bring sudden showers.