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Behind the Forecast: How much does a cloud weigh

Listen to Science Behind the Forecast with Meteorologist Tawana Andrew every Friday on 89.3 WFPL at 7:45 a.m.
Published: Mar. 19, 2021 at 8:54 AM EDT
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LOUISVILLE, Ky. (WAVE) - Clouds. They look light and fluffy so they can’t weigh much at all, right? Wrong.

First, consider this. Air is not weightless. Air pressure, or barometric pressure, at sea level, is around 14.5 pounds per square inch.

Clouds are comprised of a lot of tiny water droplets. For a cumulus cloud, the water density has been estimated to be near half a gram of water per cubic meter. A one cubic kilometer cloud contains a billion cubic meters. Doing the calculations, we find that there are five hundred million grams of water droplets in a one cubic meter cloud. That translates to about 500 thousand kilograms or 1.1 million pounds. That’s around five times as heavy as a blue whale, the largest animal in the world.

So why isn’t that weight just dropping down on us? Well, the weight isn’t concentrated in one area; it’s spread out over a large space. Also, water droplets can be so small that gravity barely affects them. Clouds are less dense than dry air so that buoyancy keeps them afloat.

Eventually, once a cloud’s water density increases, the droplets also get larger (and heavier), and the cloud will fall as rain.

The density of other types of clouds would affect their weight. For example, a cumulonimbus cloud would be heavier than cumulus clouds due to it being made up of more water droplets.

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