Cap Cloud

2010-09-21 17:51:25.000 – Mike Finnegan,  IT Observer

Cap Cloud

We are about as close to being in the fog as we can be here on the summit without actually going into it. The phenomenon we are currently experiencing is referred to as a cap cloud. It is a form of wave cloud, related to lenticulars, those clouds often mistaken for UFOs. In the case of the cap cloud, it forms as moist air is push up and over the mountain. Given the right conditions, this air condenses into a cloud below the mountain’s summit. However, the orographic movement forces the air over the summit, leaving the summit in the clear, but with a cloud just overhead. On the backside, the air falls back down the mountain and the cloud in turn dissipates. Tonight we experienced a cap cloud whose edges below the station limited visibility to a mere quarter mile in all directions. The ceiling overhead was only perhaps 50 feet. Still, we recorded a relative humidity of 80% (compared to 100% when in the fog).

We saw several wave clouds earlier today forming to our north. They were often changing every few seconds, a remarkably ephemeral spectacle to watch. Fortunately, there were several people on the summit at the time so many were able to appreciate this view. I feel very fortunate to experience so many cool weather features, but it is also nice to be able to share it with others, either in amazement or technical understanding.

Mike Finnegan,  IT Observer