1 Photo Gallery: Clouds Fluffy altocumulus undulatus clouds stain the sky red above a row of trees.

2 Lenticular clouds technically known as altocumulus standing lenticularis are stationary lens-shaped clouds that form at high altitudes.

3 Altocumulus lacunosus. “An elusive prize for any cloud collector,” lacunosus clouds form when sinking pockets of air create holes in a cloud layer.

4 Ripples of altocumulus or cirrocumulus clouds—resembling the markings of a king mackerel—give the phenomenon its name.

5 Altocumulus clouds, embedded in the altostratus cloud, can be seen at left.

6 Altocumulus clouds are small cumulus clouds that are knitted tightly together. These storm clouds often darken the land.

7 Altocumulus clouds are typically layers or patches of cloudlets, and in the lenticularis variety they are candidates for “weirdest looking clouds in the sky.

8 Fluffy altocumulus undulatus clouds stain the sky red above a row of trees.

9 They are referred to as "alto" clouds and bear such names as altostratus, which are flat, or altocumulus (pictured), which are puffy.

10 The time was 1:00 PM, and the visibility was excellent with some altocumulus clouds.

11 They are long streaks where ice clouds are continuously being formed as the aircraft travels in the altocumulus cloud layer.