Which cloud type is the primary sign of a thunderstorm?

• A. Fog forming
• B. Droplets of drizzle
• C. Low, dark stratus clouds
• D. Towering cumulonimbus

Answer: (D)

Thunderstorms take shape from strong convection lifting warm, moist air high into the atmosphere, building a tall, dense cloud known as cumulonimbus. This cloud is the telltale sign because its vertical reach and structure fuel the intense weather of a thunderstorm—heavy rain, lightning, thunder, and sometimes hail. Fog forming, drizzle, or low, dark stratus clouds describe different weather scenarios: fog sits near the ground with calm, misty air; drizzle indicates light rain; and low stratus just blankets the sky without the deep vertical development that leads to a thunderstorm. So, the towering cumulonimbus cloud is the hallmark of a thunderstorm.