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How to identify the varieties of low clouds

Posted by mandyf on May 3, 2012

Everyone has looked up to the sky gazing at the clouds looking for familiar shapes, signs of the weather to come, or plain old curiosity. Most of the time though people have little real idea of what the clouds mean or are even correctly called. Learning how to identify the clouds we see everyday really isn’t as difficult as you might think. While there are literally so many variations it could make your head spin, if you stick to the official U.S. DOD (Department of Defense) Weather Observers Training Guide For Block One Education, it does make things infinitely simpler, which is oddly enough the opposite of most things military.

For starters there are three basic types of clouds which are broken down by height, the low, middle and high clouds. In this article we will deal only with the low clouds which range to a height 50 feet to 6,500 feet. Anything from 50 feet or under is classified as fog although it’s composition is exactly the same as a cloud. It’s a small distinction but worth note none the less. While there are 9 low clouds, just as there are 9 middle and 9 high clouds, there are seven varieties of low clouds, eight if you count the two varieties of low cloud number 9. It sounds confusing at first but it does get simpler.

The low cloud types we need to be concerned with are the following: Stratus, Ninmbostratus, Stratocumulus, Cumulus, and Cumulonimbus.

Cumulus are the most common you will see on any given day. These are easy to spot as they are the big white puffy clouds that look like cotton candy. You will notice they have flat bottoms but those big billowy tops. These are the very clouds people often see interesting shapes in. Not to destroy the magic for anyone, but this is just a product of condensation. As warm air rises and cools, it still remains warmer than the surrounding air which causes the vapor to condense and the appearance of big puffy tops.

Stratus clouds appear in sheets that are thin and fragmented in appearance. Unlike a cumulus cloud which tends to blot everything out, a stratus cloud will allow the observation of the sun or moon through their thin veil almost all the time. These can further be differentiated from cumulus clouds because they lack vertical development of any significance. Imagine what a flattened cloud would look like and that is stratus type formation. Stratus clouds move with the direction of the wind, and generally appear to move faster than everything else in the sky.Eventually stratus clouds may form into stratocumulus clouds.

Stratocumulus clouds look like the offspring of a stratus and cumulus cloud. They have the long sheet like base which is now less fragmented and thin with the addition of vertical development. These clouds tend to grow more vertically than horizontally and will move faster than a cumulus, but slower than a stratus cloud under most conditions. They will almost always appear dark at the bottom and light at the top which helps further distinguish them from stratus clouds. The interesting thing is that stratocumulus clouds can be formed from stratus (Escalating) or cumulus clouds (Degenerating) which is why they often still have a fragmented appearance (breaks) in which the sun or moon can be observed through depending on the size of the break.

Nimbostratus clouds are very interesting in that they can form as low as 150 feet off the ground, but thicken up to somewhere in the area of 15,000 feet! Nimbostratus clouds are dark and huge which makes them distinctly stand apart from everything else in the sky. While these don’t always deliver weather, but when they do it is generally long continuous rain showers or snow depending on the temperature. You will not see the sun or moon through a nimbostratus cloud, nor will they have breaks. One of the easiest ways to think of a nimbostratus cloud is to liken it to a cumulus cloud on way too many steroids.

There are still more varieties in the low cloud family to look at, the first of which is Towering Cumulus or TCU. A TCU is a cumulus cloud which as the name suggests has taken on great vertical development. The easiest way to think of this is to picture Marge Simpson’s hair. While it won’t be that thin, it will look quite similar as if a large base has suddenly channeled all of it’s developmental power to the middle of the cloud and then straight up.

The final type of low cloud is cumulonimbus, although this comes in two varieties. A cumulonimbus cloud can best be thought of as a TCU which is having trouble making up it’s mind. It has a strong cumulus bas development, but continues towering upward from the middle. It develops vertically and horizontally at almost the same rate. The base of the cloud will often look like it has hanging sacks that are waiting to burst. Not always, but sometimes, the top will form into what looks like an anvil. When this happens and the hanging sacks are present still, this is now a cumulonimbus mammatas. When you see this cloud cancel the picnic and watch a movie.

Identifying the low cloud varieties is quite easy once you have an idea of what to look for. Technically speaking you could go on for quite some time further breaking the cloud types down into fractocumulus, fractostratus, etc…, but that is of more use to academics than the casual or even professional observer. The next time you go out you’ll have some idea of what is you’re looking at when you peer into the sky.

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