|Date||26 June 2011|
|Location||A5, Nant y Benglog||SH 67497 60439; 53.12459°N, 3.98161°W|
Normally found in the lee of a mountain, Altocumulus lenticularis is a ‘wave’ cloud created when a standing wave forms in the flow of air forced to rise up over the mountain. Water vapour in the air travelling in the wave condenses to form the cloud when it reaches the crest of the wave when the temperature there is low enough, and then evaporates again as it sinks back down into the warmer trough.
Lenticular clouds remain stationary but are continuously being formed as the moisture in the air flowing through them condenses and then vapourises again. They are smooth and lens shaped, and this saucer-like appearance can lead to their being confused for UFOs.
These stacked lenticular clouds were observed from the A5 road just east of Tryfan in the pass between the Carneddau and Glyderau mountain ranges.
Featured in NASA Earth Science Division’s Earth Science Picture of the Day, 26 July 2011.