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What causes precipitation (rain and snow)?
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| Precipitation forms when cloud droplets (or ice particles) in clouds
grow and combine to become so large that the updrafts in the clouds can no longer support them,
and they fall to the ground. The more water vapor there is below the cloud, and the stronger the updrafts
that cause this water vapor to condense into cloud water or ice particles, the more likely it is that precipitation will form
within the cloud. A cloudy day with no precipitation indicates that there is either not enough water vapor available
to the cloud, or that the rising motion creating the cloud is not enough to cause precipitation (or both). At
the opposite extreme is a tropical rain shower that has large amounts of water vapor available to it (like the
one pictured above), and
which can rain heavily from even a small cloud.
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| Interesting facts:
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| PRECIPITATION EQUALS EVAPORATION All of the precipitation that falls
originated as water vapor that was evaporated from the surface of the Earth. It is always raining somewhere on the
Earth, just as evaporation is always occurring over most of the Earth's surface. At any given time, precipitation
covers only about 2% to 5% of the surface of the Earth, while evaporation is occurring over the remaining 95% to 98%
of the Earth. Thus, water vapor gets "concentrated" into relatively small rain systems that turn this vapor into
precipitation.
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