The Clouds Floating

The clouds floating overhead contain water vapor and cloud droplets, which are small drops of condensed water. These droplets are way too small to fall as precipitation, but they are large enough to form visible clouds. Water is continually evaporating and condensing in the sky. If you look closely at a cloud you can see some parts disappearing (evaporating) while other parts are growing (condensation). Most of the condensed water in clouds does not fall as precipitation because their fall speed is not large enough to overcome updrafts which support the clouds. For precipitation to happen, first tiny water droplets must condense on even tinier dust, salt, or smoke particles, which act as a nucleus. Water droplets may grow as a result of additional condensation of water vapor when the particles collide. If enough collisions occur to produce a droplet with a fall velocity which exceeds the cloud updraft speed, then it will fall out of the cloud as precipitation. This is not a trivial task since millions of cloud droplets are required to produce a single raindrop. A more efficient mechanism (known as the Bergeron-Findeisen process) for producing a precipitation-sized drop is through a process which leads to the rapid growth of ice crystals at the expense of the water vapor present in a cloud. These crystals may fall as snow, or melt and fall as rain.

Care to guess how many gallons of water fall when 1 inch (2.5 cm) of rain falls on 1 acre of land?

What do raindrops look like?

The USGS water drip icon, Drippy, who is in the shape of a drip.Let me introduce myself - I am Drippy, the (un)official USGS water-science icon. It is obvious that I am a raindrop, right? After all, all of you know that raindrops are shaped, well ... like me. As proof, you've probably seen me on television, in magazines, and in artists' representations. Truth is, I am "Drippy" and actually I am shaped more like a drip falling from a water faucet than a raindrop. The common raindrop is actually shaped more like a hamburger bun.

Image of raindrops at about different sizes - shaped like a hamburger bun at 3 millimeters.As Alistair Frasier explains in his web page, Bad Rain, small raindrops, those with a radius of less than 1 millimeter (mm), are spherical, like a round ball. As droplets collide and grow in size, the bottom

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