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Fair Weather Cumulus Clouds | Hey Ray!

Fair Weather Cumulus Clouds | Hey Ray!
Fair Weather Cumulus Clouds | Hey Ray! 02:00

PITTSBURGH (KDKA) - On beautiful days full of sunshine, sometimes some puffy clouds develop that look like cotton balls.  These "fair weather cumuli" form because of certain atmospheric conditions.


You can tell a lot about the weather from the clouds, or even the lack of them! Obviously, clouds come in all shapes and sizes. Some are associated with storms. Some bring snow. Others...well they just seem to show up for picture purposes.

Those are the clouds that look like cotton balls on nice days and are called "fair weather cumulus" clouds.


Cumulus clouds are individual clouds. That means you usually see separate clouds when they develop instead of just a gray sky. 

Usually, they have a flat or sort of flat underside and a sort of rounded top. They grow vertically, meaning they usually start very small and then develop upward.  

Ray Petelin

The National Weather Service says the different types of cumulus clouds are named depending on how high they develop. The clouds that show little vertical growth on an otherwise sunny day used to be termed "cumulus humilis" or "fair weather cumulus". 

Many people just say cumulus, but their distinction tells you a lot about the weather. They don't grow as high into the atmosphere as a cumulonimbus (thunderstorm) cloud. There is a reason for that.

All clouds develop because of the water cycle.  Moisture is lifted into the atmosphere after the Sun heats the ground. If you think about it, the Sun is very efficient on a nice, sunny day.  Those sunny days are the days that you see these fair weather cumuli.  


High pressure is usually what brings us beautiful, sunny weather. It is a large area of sinking and drying air. That is important for fair weather clouds. 

As the sun heats the ground and lifts moisture up, high pressure is pushed downward. With those two forces, you end up with a squished cotton ball of a cloud.  

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