Grades K–2 · Earth & Space
How can tiny cloud drops become rain?
A cloud can drift overhead without a single raindrop reaching the ground. It holds many tiny water drops, tiny ice pieces, or both. The drops are already pulled downward by gravity, but they settle slowly. Upward-moving air can help carry them along.
In the diagramTiny cloud drops can grow into rainEnlarged viewWater gathers into bigger dropsSome clouds also contain tiny ice crystals.Cloud water must grow before it falls as rain.
Some drops bump together and join. A bigger drop can fall through air more readily than a tiny cloud drop, so growing drops can begin falling faster than the rising air carries them upward. Ice pieces can grow too, then melt into drops as they pass through warmer air.
If these falling drops reach the ground, we call it rain. Some become invisible water vapor before they arrive. A cloud is therefore not simply a bag that opens: many tiny pieces of water must grow and travel through changing air before rain reaches a roof or a puddle.
About this explanation
Starting knowledge: Recognize a cloud, liquid water drops and rain falling toward the ground.
Sources
- National Weather Service — Weather Education: Precipitation