Kind: captions
Language: en
Although weather is a description of the
state of the atmosphere at a specific
time and can include references like
sunny, partly cloudy, or drizzly, the
types of weather people tend to care
about most are severe storms.
So, what causes a calm day to suddenly
turn violent or even deadly? And why do
some storms live on for hours or even
days?
To understand storms, you have to
understand clouds, which form when warm
air rises from Earth's surface toward
the higher and colder reaches of the
atmosphere. This upward motion can
result when a colder, denser air mass
pushes under a warmer one and forces it
upward, or when a patch of ground
absorbs more heat than its surroundings
and transfers that heat to the air
above, causing it to rise.
Severe storms like thunderstorms,
blizzards, and hurricanes require three
conditions to develop and maintain their
potentially devastating power. an energy
source, moisture, and unstable air. The
energy for big storms can come from
temperature differences between two air
masses, or more often, from heat
absorbed by Earth's surface that warms
the air above it. It's the same process
that creates clouds, but on a larger and
more extreme scale. The warmer the
ground or ocean water below a developing
storm, the more energy it can transfer
to the storm as it grows.
Severe storms also require huge amounts
of moisture. Not only is this moisture
necessary to produce a storm's
precipitation, but it also carries the
storm's energy from Earth's surface to
the upper reaches of the atmosphere.
The energy is transported by water
vapor, which is produced when light from
the sun heats up liquid on Earth's
surface, causing it to evaporate. The
vapor holds on to that energy until it
condenses and transitions back into the
liquid water droplets and ice crystals
that make up a cloud. When that happens,
the vapor releases the stored energy in
the form of heat, which fuels the
storm's growth. The final critical
factor in the formation of severe storms
is for the air surrounding the storm to
be significantly colder than air at
lower levels. Scientists call this
unstable air. So, as a storm cloud rises
and releases heat, it continues to be
surrounded by colder air, which allows
it to rise even further. Basically, the
greater the temperature difference
between a storm cloud and its
surroundings, the faster, higher, and
more intense it will grow. When all
these conditions are in place, a rich
source of energy, lots of moisture, and
unstable air above, severe storms are
sure to develop. Just how powerful a
particular storm will be depends on how
extreme those conditions are, and they
can be very powerful. The most severe
thunderstorms can drop more than 2 in of
rain per hour and generate winds of more
than 200 mph.
When multiple thunderstorms form near
each other in an area over warm ocean
water, they can combine to form the
start of a hurricane, Earth's most
powerful and devastating type of storm.