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Unformatted text preview: ted water drops, then the water freezes onto the
ice. As the snowflakes grow larger, they fall. If the air temperature near the
ground is above freezing, the snow will turn to rain. If it is below freezing, it will
remain snow. Warmer clouds will tend to produce denser snow (wet snow good
for snowballs) while colder ones produce less dense ‘powder’ (good for skiing).
Hail forms when ice crystals fall and may start to melt, but then are caught in an
updraft and re-freeze higher up. While falling, they come in contact with more
liquid water that becomes attached and freezes. Then they fall again and they
can go through this process many times; each time they add a layer of ice. Most
hailstones are relatively small, but they can be large, even softball size. Big ones
can cause considerable damage. Sleet forms when rain falls though a cold layer
of air and refreezes before hitting the ground. Freezing rain is liquid when it hits,
but then quickly turns to ice. Roads can be covered in ice and tree branches can
break under the extra weight. Precipitation is the term we use for all forms of
water falling to the ground. Atmospheric Stability
Precipitation only occurs when the air rises and we are going to look at several
different ways to get air to rise. But first let’s look at the concept of atmospheric
stability. This refers to how easily air will rise. If air is stable, it can be pushed
up, but then will drop back down. Unstable air will keep rising. A parcel of air
warmer than the air around it will rise because it is less dense. It will stop rising
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This document was uploaded on 10/27/2011 for the course GEOG 1401 at Texas Tech.
- Fall '08