Questions: Clouds and Rain

Question 1

Why do some clouds look white and fluffy while others are dark and heavy-looking?

• A. Dark clouds are older than white clouds
• B. White clouds are thin and let sunlight pass through; dark clouds are thick and tall, blocking more sunlight
• C. Dark clouds are made of a different kind of water
• D. The sun changes the color of clouds based on the time of day

Answer: (B)

All clouds are made of water droplets (or ice crystals). The difference in appearance is about thickness. Thin clouds let sunlight scatter through them, appearing white and bright. Thick, tall clouds block most sunlight from passing through, so their bottoms appear dark gray. The darker the cloud base, the taller and water-packed the cloud usually is -- and the more likely it is to produce rain.

Question 2

Most cloud you see will eventually produce rain.

• T. True
• F. False

Answer: False

Most clouds never produce rain. The tiny droplets in many clouds are too small and light to fall -- they stay suspended in the air. Only when conditions cause droplets to grow large and heavy (by colliding and merging with other droplets) does rain fall. Many fair-weather cumulus clouds form and evaporate without ever producing a single raindrop.

Question 3

You see tall, dark clouds building in the sky. What type of weather might they bring, and why?

Model answer: Tall, dark clouds are likely cumulonimbus clouds, which bring thunderstorms with heavy rain, lightning, and sometimes strong winds or hail. They are dark because they are so tall and thick that they block most sunlight. Their height means they contain a huge amount of water, which is why they produce the heaviest rain.

Connecting cloud appearance to expected weather is the practical payoff of learning about cloud types. Being able to look at the sky and predict what is coming is one of the most useful skills in observational weather science.