Which cloud type is high, thin, and often signals a change in weather?

• A. Cumulus clouds
• B. Stratus clouds
• C. Cirrus clouds
• D. Cumulonimbus clouds

Answer: (C)

Cirrus clouds form high in the sky, well above 20,000 feet, and are made of ice crystals that give them a thin, wispy appearance. Because they ride in the upper levels of the atmosphere, they often stretch ahead of an approaching weather system, acting as a signal that weather changes are on the way—typically within hours to a day or two. In contrast, cumulus clouds are puffy and lower, usually signaling fair weather or developing instability; stratus clouds blanket the sky in flat layers and bring steady light rain or drizzle; cumulonimbus clouds are tall and dark, bringing strong thunderstorms. So the high, delicate nature of cirrus clouds and their tendency to precede incoming weather makes them the best indicator of a change in weather.