[MUSIC] Joan Cartan-Hansen, Host: Scientists classify clouds based on altitude, shape and what kind of weather happens when those clouds are around.

First, the low-level clouds: Cumulus clouds are puffy, white, and happen early in the day.

Stratocumulus clouds are low and fluffy.

And finally, stratus clouds are gray, flat and are similar to fog.

Next are the mid-level clouds: Altocumulus are fairly common and look like white or gray patches.

Altostratus clouds make a white or gray blanket about mid-level in the sky.

And nimbostratus clouds form a dark layer across the sky.

And finally, the high-level clouds.

Cirrocumulus clouds are small, and sometimes are arranged in parallel rows.

Cirrostratus clouds are white and wispy.

Cirrus clouds are thin and white.

Cumulonimbus clouds are dark and dense Technically, they are low-level clouds but can have towering parts at high levels.

These are the thunderstorm clouds.

[THUNDERCLAP] For more information about the weather, check out the Science Trek website.

You'll find it at science trek dot org.