photo #5375811

These stacks of lenticularis clouds formed over North Canterbury, New Zealand during a weather event, when the winds exceeded, at times, 160 mph (260 km/h). Spotted by Kitty Frederikson (Cloud Appreciation Society Member 44,548) in the golden light of the evening, they’re known more specifically as Altocumulus lenticularis duplicatus clouds. And despite being formed by such fierce winds, these clouds would have remained pretty much stationary in the sky. Why? Because lenticularis clouds form in invisible standing waves of air, when the flow rises and dips downwind of a mountain range. The cloud droplets form where the air cools as the flow rises in a crest and evaporate away again where it warms as it dips beyond. Like standing waves downstream of boulders in a fast-flowing river, the positions of the cloud-forming crests stay fixed in place relative to the mountains no matter how strong the wind