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 Just
about everyone
can identify with the events leading up to a severe thunderstorm.
Even from early morning, you can tell that there will possibly be
storms today, just by the humid feel in the air. The "muggy"
feeling is oppressive, even sometimes making it harder to breathe.
Then by mid-afternoon, during the hottest part of the day, you sense
the first signs of an on-coming storm. First you hear that distant
rumble of rolling thunder. Curiously you peek out the window just
as a flash of lightning catches your attention. It is coming from
a towering mass of black clouds sitting in the western sky. Moments
later the wind increases, rattling the window panes.The sun is soon
overtaken by the giant thunder-head, and a wall of rain creeps ever
closer, bringing water droplets down in sheets.
But what will be next? Will there be hail, flooding, a tornado? How
can you find out, and what safety tips do you need to follow? The
following page will tell you just that.
A thunderstorm develops when
warm, moist, unstable air rises in the atmosphere (This usually
occurs along areas called fronts, the point at which
masses of cold air and warm air meet, the specific point of
collision being the dry line.). As this air meets cooler
air that has a tendency to sink, a horizontal circulation occurs
between the two masses, causing the air to rise to greater altitudes.
As the warm, moist air condenses, huge mushroom or anvil-shaped
clouds (often called super cells) filled with rain, lightning,
wind, hail, and tornadoes form. The more extreme this meeting
is, the more intense the energy exchange is, and therefore more
intense storms form. As a rule, the taller the cloud tops, the
more intense the thunderstorm is. Specifically, a thunderstorm
needs to have at least one of the following to be classified
as severe: winds of at least 58 mph, 3/4 inch hail, or the occurrence
of a tornado.
Lightning, hail, wind, and tornadoes,
are all bourne from the energy and movement that is created
and occurs within a storm cloud. As the movement of warm and
cold air increases, wind is created. This movement also
causes the positively and negatively charged particles within
the cloud to polarize (collect at the ends of the cloud - negative
at the base, and positive at the top). Because opposite particles
attract, these particles will eventually move toward one another,
resulting in lightning, whether it be within the same
cloud, cloud to cloud, or cloud to ground (the ground is positively
charged). Thunder is the rumbling sound made when the
atmospheric gases are rapidly heated by a lightning bolt.
Hail,
another manifestation within a thunderstorm, is formed from
the rapid movement of water particles within a cloud. The air
is moving them so quickly around the cloud that they do not
immediately fall. Instead, they begin to freeze, and form balls
of ice. When their weight is able to overcome the wind speed,
they fall to the ground as hail. In some of the most severe
thunderstorms, hail has fallen that was the size of softballs.
Tornadoes are probably
the most feared of all factors of a severe thunderstorm. Movement
within a thunderstorm become so great that a column of air extends
down to the ground, rotating violently, leaving destruction
behind as it moves along the ground. Please see our tornado
page for more information and safety tips.
It
is important to be aware of any severe thunderstorm watches or warnings
posted for your area so that you may be able to take the appropriate
safety precautions. A severe thunderstorm watch means that
conditions are favorable for the formation of severe thunderstorms
in your area. At this time you should review safety plans of action
and tips. A severe thunderstorm warning, means that a severe
thunderstorm has developed in your area, and you should take cover.
Please see "THUNDERSTORM SAFETY TIPS" for more information.
THUNDERSTORM
SAFETY TIPS
*THUNDERSTORM
FACTS OBTAINED FROM NOAA
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