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Thunderstorms
Thunderstorms affect
relatively small areas when compared with hurricanes and
winter storms. The typical thunderstorm is 15 miles in
diameter and lasts an average of 30 minutes. Nearly
1,800 thunderstorms are occurring at any moment around
the world. That's 16 million a year!
Despite their
relatively small size, all thunderstorms are dangerous.
Every thunderstorm produces lightning, which kills more
people each year than tornadoes. Heavy rain from
thunderstorms can lead to flash flooding. Strong winds,
hail, and tornadoes are also dangers associated with
some thunderstorms.
Of the estimated
100,000 thunderstorms that occur each year in the United
States, only about 10 percent are classified as severe.
The number one
thunderstorm killer is flash floods/floods which kill
nearly 140 people each year.
Most flash flood
deaths occur at night, and when people become trapped in
automobiles.
Lightning occurs with
all thunderstorms. Lightning averages 93 deaths and 300
injuries each year. It causes several hundred million
dollars in damage to property and forests annually.
Straight-line winds
are responsible for most thunderstorm wind damage. Winds
can exceed 100 mph. One type of straight-line wind, the
down burst, can cause damage equivalent to a strong
tornado and can be extremely dangerous to aviation.
WHAT MAKES A THUNDERSTORM?
Every thunderstorm
needs:
-
Moisture - to
form clouds and rain.
-
Unstable air -
relatively warm air that can rise rapidly.
-
Lift - fronts, sea
breezes, and mountains are capable of lifting air to
help form thunderstorms.
The action of rising
and descending air within a thunderstorm separates
positive and negative charges. Water and ice particles
also affect the distribution of electrical charge.
Lightning results from the buildup and discharge of
electrical energy between positively charged areas. The
air near a lightning strike is heated to 50,000 degrees
F -- hotter than the surface of the sun. The rapid
heating and cooling of air near the lightning channel
causes a shock wave that results in thunder.
LIFE
CYCLE OF A THUNDERSTORM
Developing Stage:
-
Towering
cumulus cloud indicates rising air.
-
Usually little
if any rain during this stage.
-
Lasts about 10
minutes.
-
Occasional
lightning during this stage.
Mature Stage:
-
Most likely
time for hail, heavy rain, frequent lightning,
strong winds, and tornadoes.
-
Storm
occasionally has a black or dark green appearance.
-
Lasts an average
of 10 to 20 minutes, but may last much longer in
some storms.
Dissipating Stage:
-
Rainfall
decreases in intensity.
-
Some
thunderstorms produce a burst of strong winds during
this stage.
-
Lightning remains
a danger during this stage.
WHICH WAY DOES LIGHTNING TRAVEL?
A cloud-to-ground
lightning strike begins as an invisible channel of
electrically charged air moving from the cloud toward
the ground. When one channel nears an object on the
ground, a powerful surge of electricity from the ground
moves upward to the cloud and produces the visible
lightning strike.
ENVIRONMENTAL CLUES
When skies darken or
thunderstorms are forecast, look and listen for
increasing wind, flashes of lightning, sound of thunder,
and static on your AM radio.
HOW FAR AWAY IS THE LIGHTNING
To estimate the
distance in miles between you and the lightning flash,
count the seconds between the lightning and the thunder
and divide by five.
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