The Mountain Cloud

The photo was taken by Becky Powell.

The photo was taken by Becky Powell.

Last Sunday afternoon, those who looked at Cumberland Mountain from the Tennessee and Virginia side got to see a beautiful cloud formation that draped over the top half of the mountain. I’ve seen it do that on only a couple of times, so it’s not that common and was awesome to see. I got to wondering what was going on to cause the phenomena, so what follows is my best shot at amateur meteorology.

The cloud was actually formed by the mountain itself, something the weather guys call orographic clouds. They form when air is forced upwards as it passes over a mountain, and can be anything from a light mist to heavy and thick depending on how much moisture is in the air.

So here is what I think was going on. I was able to look at weather data on line from Cumberland Gap National Park’s weather station that’s located near the visitor center in Middlesboro. It showed that on Sunday, September 7, the air was very humid, 80-90% all day. Also, the wind shifted around and started coming out of the north starting around noon. So very moist air was pushed by a north wind up the Kentucky (north) side of Cumberland Mountain. Air cools as it gains elevation, and so at the top the moisture condensed and formed a thick cloud that meteorologists classify as “stratocumulus”. The wind continued to push the cloud over the top and spilled it over onto the Tennessee/Virginia (south) side of the mountain. As the cloud rolled down the south side, it warmed as it fell, until the cloud particles evaporated about half way down the slope. This created a white shroud that appeared to be stationary over the mountain, but was in fact continuously rolling from the north side to the south side. It was amazing how straight the bottom of the cloud was, as if God drew a line to indicate where it would stop. Our prevailing winds come out of the southwest, so the combination of very humid air pushed by a north wind doesn’t happen often.

In fact, in my research I did not find many references to this type of mountain cloud. A common denominator I did find is a fairly high mountain (often a plateau) above a substantial valley, which is exactly what we have here with Cumberland Mountain and Powell Valley. There is a well know stratocumulus cloud that regularly forms on Table Mouintain above Cape Town, South Africa. There the prevailing wind pushes air that gathers moisture as it moves over a body of water and when it hits the mountain it regularly forms a cloud that is locally called the Tablecloth cloud, and is very picturesque.

It looks a lot like what was seen here Sunday.

So there you have it, another example of creation where natural science generates natural beauty. Very cool….

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