This post originally appeared on Nature Education’s Student Voices
When you’re flying, you see more of the world. You see the shimmer of lakes and oceans only available at high altitude. You pass serenely through giant fluffy clouds. If you get high enough, you can see a blanket of those clouds shadowing vast stretches of the Earth’s surface. For all you get to see at this scale, you do miss one thing about clouds: the billion pounds of water they carry.
Clouds, no matter the species, can be absolutely massive. A typical thunderstorm can be miles high and miles wide – enough space for what looks like a dense fog to contain a biblical amount of water. An average thunderstorm can contain 2.3 billion pounds of water. It would take a full six minutes for an equal amount of water to go over Niagara Falls.
The enormous weight of a cloud conflicts with what we usually think is light enough to float. But it is its volume that betrays our common sense. Surely something a billion pounds would fall right out of the sky and absolutely devastate the surface? But spread that weight out over cubic miles and you wouldn’t even think a cloud was heavy.
If you were to stroll a few meters through an average cloud, walking on cloud nine, as it were; you would only encounter a few grams of water. It would be a pleasant misting, something akin to those sprayers that keep the patrons of Six Flags cool on hot days. Even walking through a storm cloud would hardly drench you (though it would depend on where you walk). For a comparison, each of your feet can produce up to a pint of sweat a day. You could amble through 470 cubic meters of cloud – six and a half times the volume of a freight container – before you encountered the same amount of liquid.
A cloud floats because of how spread out its mass is. It’s so spread out that wind currents overcome the force of gravity on the microscopic droplets. Only when enough of these droplets knock into each other do they begin to throw their weight around. That’s when we get out our umbrellas.