· Dee Marshes, Gayton ·
Strange, rippled cloud-patterns over North Wales in the late afternoon. Then, at dusk, two lenticular clouds above the Clwydian Hills. Lenticular, meaning lentil-shaped (a tiny pulse that, from its shape and its Latin root, also gives us the word lens).
Lenticular clouds usually form above hills. Winds passing over the hills create turbulent eddies. Less turbulent, moist air passing above these eddies forms standing waves downwind of the hills. When the conditions are just right, the tops of these waves cool sufficiently to produce flat-bottomed, saucer-shaped clouds. Or UFO-shaped clouds, for the more sci-fi inclined.