photo #4285960

Ever since she saw an Altocumulus lenticularis cloud featured as one of our Cloud-a-Days, Sandra Wu (Cloud Appreciation Society Member 53,154) dreamed of adding one to her cloudspotting collection. One day, while she was motoring home to Oregon from California, Sandra’s wish finally came true. She noticed this UFO-shaped cloud downwind of Mt. Shasta. The flow of winds over the Cascades Range of mountains set up the right rising and dipping air current for a disc of cloud like this to appear. The wind’s smooth, steady ascent and descent downwind of the peak is known as a standing wave of air. It can form a smooth, steady cloud when it carries enough moisture for droplets to condense up at the crest of the mountain wave of air. To the right of Sandra’s cloud appears the edge of an undulatus variety of Altocumulus lenticularis mostly out of frame. This one is called undulatus because it had a rippled pattern across part of its disc, caused by wind speeds varying greatly with height. It was another for Sandra to add to her collection: ‘Two amazing formations in one stop!