photo #6105864

Mark Bushnell (Member 57,127) noticed a strange, elongated cloud from his upstairs window one spring day in Middlesex, Vermont, US. ‘It made me think there was something wrong with my eyes,’ he told us, ‘– as if a normal cloud had been unrealistically stretched across the scene like a poorly rendered panorama photo.’ The cloud is in fact an Altocumulus lenticularis, and it forms when moist, stable winds flow over hills or mountains, taking on wavelike paths downwind of the terrain. Cloud droplets condense where the air cools at the wave peaks. An individual mountain can lead to a flying-saucer-like disc of cloud, which sometimes has a stacked appearance if the airflow consists of alternating moister and drier layers. An elongated, lozenge-shaped lenticularis like Mark’s is the result of air flowing over an extended mountain range like Vermont’s Green Mountains. Either that, or Mark just got the panorama settings wrong on his smartphone.Happy World Meteorological Day!