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© NOAA
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Sunset and a small rain storm across the river.
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Raindrops are formed when the cloud droplets grow big enough to fall
out of the clouds. Most of the rain that falls in the winter, and even
a lot of it that falls in the summer, is from melting of snowflakes as
they fall through warmer air.
Rainfall is measured by the depth of water that falls on a level surface
without soaking in. Rainfall is measured with a rain gauge. A basic rain
gauge is nothing more than a cylindrical container, like a metal can,
with a flat bottom. The only problem is to get an accurate measurement
of the depth of water that has fallen. Accurate rain gauges are arranged
so that the water that falls into the container is funneled into a much
narrow container inside. That way, the height of the water is magnified,
and is easier to read.
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© NOAA
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8-inch rain gage. The type of rain gage used by the Weather
Service since the late 1800's.
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If you live in a part of the United States where it snows in winter,
you can easily measure the snow depth with a ruler. The best time to make
the measurement is right after the snow stops falling. The measurement
can be tricky, because wind can blow snow from one place to another. The
best place to measure snow depth is on level ground far away from buildings
and trees.
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