Download Thunderstorms

Thunderstorms
What Are Thunderstorms?
• Thunderstorms are the most common
kind of severe storm. They form in clouds
called thunderheads, or cumulonimbus
clouds. The storms cause huge electric
sparks called lightning. The lightning
heats up the air and causes the noise
thunder. Thunderstorms usually have
heavy rains and strong winds.
• A thunderstorm starts when intense
heating causes air to rise very quickly.
• A cloud forms where there is an upward
rush of heated air, an updraft. As more
warm, moist air is carried upward, the
cloud grows larger.
• Strong updrafts keep water droplets and
ice crystals in the cloud, so they grow in
size, too. When the updrafts can’t support
them anymore, they fall as heavy rain or
hail.
• Once the rain falls, it causes downdrafts in
the cloud.
• When the air going up rubs against air going
down, static electricity builds up.
• When enough builds up, there’s a huge
spark—lightning. Lightning may jump within
a cloud, between two clouds, or between a
cloud and the ground.
How and Where Do Tornadoes
Happen?
• The most violent thunderstorms often spin
off even more dangerous storms, called
tornadoes. A tornado is a violent whirling
wind that moves across the ground in a
narrow path.
• A tornado is a sort of runaway convection
cell.
• When the updraft in a convection cell is
really strong, the air rushes in from all
sides at high speeds. The air curves into
a spin. This lowers the pressure even
more. Air rushes in even faster, and the
pressure gets even lower, and so on. Like
a spinning skater who pulls her arms in
close to her sides, the spinning tornado
gets faster and faster.
• As the tornado gets stronger, a funnel
forms that eventually touches the ground.
In the center of a tornado, winds can reach
speeds of 500 km per hour (about 300 mi
per hour) or more.
Hurricanes
• Hurricanes are very large, swirling storms with
very low pressure at their center. They form
over tropical oceans near the equator.
• Hurricane winds whip up large waves in the
ocean. These waves move outward from the
storm and pound against a shore for days before
the storm arrives. However, it is the storm surge
that causes the most destruction. Storm surge
or storm plunge is a great rise of the sea along a
shore. Its main cause is low air pressure.
How Can Radar Track Storms?
• Storms are hard to predict because they
form so quickly. Scientists use the best
methods possible to try to identify
conditions long before a storm occurs.
They look for clues, like the movement of
fronts and the formation of very low
pressure areas.
• Special methods are used to find storms
as they form. One such method is
Doppler radar. The word radar stands for
radio detection and ranging. Radar works
by sending out radio waves and recording
their echo.
• Doppler radar is a very good tool for
scientists to track storms. The radio
waves reflect off storm clouds and are
picked back up again at the radar stations.
• Scientists use Doppler radar to find and
track thunderstorms, tornadoes, and
hurricanes. Doppler radar helps
forecasters predict which way the storms
will travel.
NEXRAD
• “NEXt generation of weather RADar”– is a newer
form of Doppler radar that is replacing older
radar systems. NEXRAD can spot small
particles such as blowing dust, very light snow,
and even drizzle.
• NEXRAD is more accurate than conventional
radar at predicting floods and flash floods. It can
show the exact locations of different fronts. It
also shows changes in wind speed and
direction. This helps scientists make more
accurate weather predictions.
THE END!