Clouds of the Day - Wednesday, August 30, 2023 Lense Shaped Clouds - Altocumulus lenticularis

Living in the mid latitudes puts us on the highway of storms. The mid latitudes are where weather systems move from west to east. It is where the polar jet streams reside and the weather is always in flux. It is also where we see many different types of clouds whose shapes change from day to day.

Below are two photos of Altocumulus lenticularis clouds. The first photo is a wide shot and the second is a closer view of the cloud located behind the tree-line.

Lenticularis are lense shaped clouds caused by waves in the air. These waves may be invisible or visible. Clouds make the waves visible.

Over low relief terrain like we have in the Midwest lenticularis are relatively rare - but they do occur often enough to be recognizable. The clouds in the photos were part of a group that was in the sky for about an hour as it moved to the southeast. They were due to gravity waves. Gravity waves occur when a layer of stable air is perturbed and moves up and down until the waves dissipate. The area of gravity waves was moving with the main flow of air to the southeast.

Altocumulus lenticularis

Altocumulus lenticularis

Lenticularis clouds are more common near mountain ranges than over the Midwest. Mountains serve as barriers to air flow. If the air is stable (it resists up and down motion), mountains force the air up and over the barrier much like water flowing over rocks in a stream. A layer of stable air causes air to flow over peaks and then to undulate up and down as it moves away from the mountains. Multiple lenticularis may form rows downwind of the peaks. Waves downwind of a mountain range often stand still. They are called standing waves. The air moves through standing waves making the clouds stationary while the air moves through.

The clouds in the photos above were not standing. Not only was the air moving through the waves the entire area of waves was moving downstream with the wind.