Stratus clouds can be hard to recognize as actual “clouds”, because they appear as a uniform, grey, horizontal layer across the sky. Stratus clouds are the “boring” members of the cloud family – they are flat and dull and appear in varying shades of grey.
Where are stratus clouds found?How are stratus clouds formed?
Fog is actually a stratus cloud occurring at ground level! Fog is formed when the air near the surface is “turbulent” meaning that an air mass near the surface cools before it has risen higher into the atmosphere.
Stratus clouds are formed with an air mass is lifted vertically into the air, and reaches a temperature cool enough for condensation to begin. Stratus clouds may turn into cumulus or cirrus clouds are air masses and moisture rise higher into the atmosphere.
What type of weather do stratus clouds bring?
Stratus clouds are not a well liked cloud because of the weather they are associated with. Usually a stratus cloud will mean a grey, drizzly day. Stratus clouds can also bring light snow if the air temperature closer to the ground is cool enough.
When stratus clouds become darker grey and heavier looking, they are what is known as nimbostratus clouds. Nimbostratus clouds are even less well-liked in terms of weather, as they are associated with bringing continuously falling rain or snow. Nimbostratus clouds are formed when a slowly rising warm air mass collides with stratus clouds. The nimbostratus cloud is a mid-altitude cloud, occurring higher in the atmosphere than stratus clouds do.
Another type of stratus cloud is the altostratus cloud. These clouds have a blue appearance, and also occur at low altitudes. The altostratus cloud also produces light precipitation such a drizzling rain. They are formed in a similar way to stratus clouds, except that condensation of the moisture in the air mass occurs because of a collision with another frontal system. Although altostratus clouds occur horizontally, unlike stratus clouds, altostratus clouds can appear as a thin horizontal line, or in the similar stacked formation.
Why do stratus clouds sometimes appear “black” in the sky?
This can be explained in two ways. First, stratus clouds are quite thick. They occur in horizontal layers, stacked on top of each other. The air and moisture within these “stacked” layers becomes opaque, and darker in colour as the thickness increases.
Stratus clouds also appear to be black based on purely optical illusion. The sky around the stratus clouds is a varying shade of blue, so there is a contrast between the darkness of the cloud and the lightness of the sky. This contrast can actually make the stratus cloud look “darker” to the human eye than it really is.