4. Mammatus (pronounced MaMa-Tuss) clouds do not
produce severe weather.
However, they are associated
with big towering
cumulonimbus clouds because
they are usually found on the
underside of an anvil cloud.
The reason some people think
Mammatus clouds mean
severe weather is coming, is
because they often appear
before a strong storm moves
in. To understand the process
of how mammatus clouds
form, let's follow a water
molecule through a
thunderstorm.
5. First the water is near the surface of
earth and in the gas form called water
vapor . In fact, you may have just
exhaled that water into the air. Then it
gets drawn upwards and becomes part
of a strong updraft within a
thunderstorm. As it ascends it
condenses and becomes part of the
towering thunderstorm cloud. But this
water droplet is still in the updraft and
goes higher and higher, eventually
freezing into an ice crystal as it reaches
57,000 feet above the surface. At that
point the upward motion of the storm is
weak and the water spreads out
horizontally, now forming part of the
Anvil cloud
6. At this point, the water is out
ahead of where the main storm
is and part of the Anvil cloud. The
ice crystal is part of a group of ice
crystals, or a moist air parcel,
which now starts to sink because
it is more dense then the
surrounding air. As the ice crystal
sinks it reaches the anvil base,
where the cloud stops and below
this point it's all clear air. The flat
cloud base forms because below
that point all moisture
evaporates.
7. However, because this ice
crystal and others in the
moist air parcel are so large,
they aren't evaporating at
that level. They continue to
sink a little farther, creating
the mammatus pouch.
8. So the Mammatus clouds
transform from ice crystal
that which now starts to
sink because it is more
dense then the surrounding
air and make the
mammatus pouch
