Altocumulus lenticularis

Shaped like a dome, the Altocumulus lenticularis or lenticular cloud appears to be still. In reality, they are indicative of unstable air. Bumping into mountainous areas, a large mass of air rises and causes a partial condensation of the water vapour contained therein. Thus forming a cloud. Once the obstacle is passed, the cloud dissolves. It is therefore in constant movement although it seems still.