Sunday, October 24, 2010

Name and explain this cloud

Frequently in large-scale southwesterly flow a beautiful cap-like cloud appears on Lone Peak, with a tail over the Traverse Range.  The cloud often ascends into a stratiform cloud deck aloft.  Indeed this is the case this morning.

This cloud is so distinctive and common that I've always wondered what this type of cloud is known as scientifically and if it has a local name.  I've called it a cap cloud for lack of a better term, but admit it looks more turbulent than a typical lenticular.

This morning's sounding shows stable conditions above 700 mb, consistent with the altostratus.  At low levels, however, the lapse rate is near dry adiabatic.

If the cloud is forming in this layer of weak stability, perhaps this helps explain the turbulent appearance.

If anyone has any good ideas or analogs from other regions, please chirp in.


  1. I pointed them out to Mara in the car the other day. I love how they look. No name though ...

  2. I've seen this most often in S or SW flow, and the appearance is especially distinctive with low-level weak stability but convective instability when a deeper layer is lifted, as over the Traverse ridge. In such cases, the low level part of the cap cloud is smooth, but often upper parts are cumuliform. My speculation is that such situations often accompany big dumps of snow in the Cottonwoods when other regions get less.