Why Does It Rain?
Date: Fall 2011
Why does it rain?
When water is heated it evaporates into the air. You cannot see the water in the air, but sometimes you can feel it (especially when it is hot outside). Have you ever noticed that on some warm days it is really humid (sticky and sweaty) and other warm days it feels dry?
You might have also noticed that in the morning, when the air is cool, you might find dew or mist on the leaves and grass. This occurs because cold air cannot hold much of moisture.
There is a limit to the amount of water that air can hold. This limit is known as the saturation limit (or dew point). When the air is completely saturated and cannot hold any more water, then it comes down as rain (and leaves all that heat in the air).
Up in Vermont, where we live, we love the rain. It turns the ground all muddy and it is a lot of fun to play in the mud!
Leslie Kanat, Ph.D.
Professor of Geology
Johnson State College
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Update: June 2012