Weird clouds at sunset - pink and lenticular

Dramatic and a bit spooky - at sunset last night.

Lenticular clouds (altocumulus lenticularis) catching the pink from the sunset and looming over Island Bay.  Their distinctive shapes are often likened to alien spacecraft - the more circular ones look like the classic "flying saucer."

These dramatic clouds usually arise from the impact of mountains or hills on the flow of a relatively moist air-stream - they behave a bit like speed bumps in the road, causing a kind of bouncing up and down movement of the air flow which is sometimes called a "gravity wave."  The clouds form on the upside of this wave flow as the rising air cools.  Other phenomena such as tall thunderclouds or winds created by a front can also act as barriers which set off this wave-like air movement, but are a much less common cause of lenticular cloud formation.

Spectacular lenticular formations are often photographed on tall mountains like Mt Shasta in the USA.  Here on Wellington's south coast we don't have any tall mountains but we do have a great combination of frequent strong winds and nearby low mountain ranges - a good nursery for these interesting clouds.  A compensation for the recent turbulent weather.