Altocumulus in Formation

Altocumulus forming in bands. The different cloud shapes are caused by differences in the air motions forming each band. Photo by Craig Johnson at Cedar Falls, Iowa.

This unusual formation features two bands of altocumulus a ribbon of blue sky with median of scattered altocumulus. The three parallel bands exhibit different cloud processes. On the left is altocumulus stratiformis undulatus. This cloud type displays an undulating flow of ripples in the flow. Note that there appear to be ripples moving left to right at a 90 degree angle to the main flow which is from the bottom to top of the photo. On the far right are altocumulus stratiformis which exhibit more of a cellular pattern of smaller cloud patches surrounded by small clear areas. This indicates different processes are involved in the formation of these two bands In the middle are altocumulus that look like a combination of cellular cloud patches but with an undulating pattern. Generally areas that are clear are regions of sinking air and or air that is not saturated or both.