Stratus

Stratus clouds are low lying clouds that form close to the ground.

They are usually flat and formless and a uniform grayish color. Many times they cover the entire sky.

Normally no precipitation is associated with these clouds, but sometimes a light mist or drizzle falls from them.

The name stratus means layer.

When stratus clouds touch the ground they are called fog.

Stratocumulus

Stratocumulus clouds form in low, lumpy layers that appear in rows, patches, or round masses with blue sky visible between individual cloud masses.

They often appear at sunset.

Usually no precipitation is associated with these clouds.

Nimbostratus

Nimbostratus clouds are a dark gray, "wet" looking cloud layer.

They are usually associated with mostly steady rain or snow, but the precipitation falling from these clouds usually isn't very heavy.