photo #5802364

The day after a major rainstorm passed through Rock Creek Park, Washington, DC, US, Bonnie Politz (Member 62,329) spotted Stratocumulus lenticularis undulatus clouds. Stratocumulus is the main classification. It is one of the ten main types of cloud. ‘Stratocumulus’ is used for any cloud that is low in the sky and appears solid looking in extended patches or layers. The term ‘undulatus’ is added when a cloud is arranged in a pattern of rolls or undulations aligned roughly perpendicular to the wind direction. ‘Lenticularis’ is included in the cloud’s classification when it forms where the air cools at the peaks of invisible rising and dipping airflows downwind of raised terrain. In a steady wind, the lenticularis form of clouds like Stratocumulus hovers in place, but it is actually a cloud in a constant state of internal motion. Its droplets form where the invisible airflow rises and cools slightly and evaporate away again where it sinks and warms. Though the positions of the rolls of this cloud remain fixed, the droplets are rushing through with the wind, just forming and dissipating at the same points. Bonnie’s storm may have passed, but the sky never stops moving.