Stratus Clouds | Universe Today

Written by Tega Jessa

There are many different types of clouds and stratus is one of the main groupings of them. All stratus clouds are generally gray, spread out, and uniform. If you have ever experienced a day that was uniformly gray with even the sun being barely visible then you have already seen a stratus cloud. They also form on foggy days as well.

Another way to describe stratus clouds is as above ground fog. They are generally formed when heavy fog starts to rise in the morning and when cold air flows over low lying regions. So if you ever hear a weather forecast that predicts a cloudy day most likely the clouds are going to be stratus.

Even within the category of stratus clouds there are several variations. These are basically combinations of stratus clouds with other types of clouds. The four main combinations are Altostratus, Cirrostratus, Stratocumulus, and Nimbostratus. Each of these clouds form at different altitudes.

Stratocumulus clouds form below 6,000 feet above sea level and they look lumpy and patchy with space of clear sky interspersed between them. These are the type of clouds you likely see on a partly cloudy day. The patch are caused by varying air temperature with the patches of sky occurring where cold air is sinking.

Nimbostratus clouds also form below 6,000 feet but they are more likely to look dark gray. These type produce precipitation which is likely to be more of a light drizzle. They are formed in when warm air flows over cold air in a wide region. This type is normally accompanied by fog and the precipitation while light can go on for a good while.

Altostratus clouds are the most familiar form of stratus clouds. They form between 6,000 and 20,000 feet. These are the type that blanket the sky. The sun is barely visible and no shadow will be able to form if these clouds are in the sky. They also produce precipitation but it is also light.

Finally, there is cirrostratus clouds. These type of clouds are interesting because it seems that they are invisible. The Sun and Moon can be seen quite clearly. The reason this happens is that they form in thin sheets at altitudes above 18,000 feet. Like other cirrus clouds there are basically floating clouds of ice crystal which explains why they seem invisible. One of the ways you can spot cirrostratus clouds is to look at the moon at night. If it has a halo around it, it is a result of cirrostratus clouds.

If you enjoyed this article there are others on Universe Today that you will enjoy. There is a great article about noctilucent clouds. There is also a great article about high altitude clouds on Mars.

There are also great resources online. There is a great article about stratus clouds on USTODAY.com. The Rice University website also has a great article about cloud types.

You can also check out Astronomy Cast. The 5/19/09 Questions episode touches on atmospheres.

Filed under: Astronomy

Tags: cloud types, low level clouds, mid level clouds