How thick must a cloud be for precipitation to form?

• A. 2,000 ft
• B. 4,000 ft
• C. 1,000 ft
• D. 6,000 ft

Answer: (B)

Droplets inside a cloud need enough vertical space to collide and grow into raindrops before they evaporate or fall apart. When a cloud is deep enough—about 4,000 feet or more—the air within supports many collisions and enough time for droplets to reach raindrop size, so precipitation can reach the ground. If the cloud is much thinner, droplets don’t have the opportunity to grow large enough, and they tend to evaporate before becoming rain. While deeper clouds can produce heavier rain, the key point is that around 4,000 feet is the typical minimum depth for rain to form.