Transcript Severe Weather (powerpoint presentation)

Severe Weather
Key Terms
• Thunderstorms
• Tornado
• Hurricane
Severe Weather
• Severe weather is weather that can cause
property damage and even death.
• Examples are:
– Thunderstorms
– Tornadoes
– Hurricanes
Thunderstorms
• A thunderstorm is a small, intense weather
system that produces strong winds, heavy
rain, lightning, and thunder.
• Thunderstorms can occur along cold
fronts.
• In order to produce thunderstorms:
– The air near the surface must be warm and
moist.
– The atmosphere must be unstable
Thunderstorms
• In order to produce thunderstorms there
must be:
– Moisture
– Unstable air
– Lift
• There needs to be moisture to form clouds
and rain. The unstable air is relatively warm
and can rise rapidly. Finally, lift can form from
fronts, sea breezes or mountains.
Lightning
• Lightning is a large
electrical discharge
that occurs between
two oppositely
charged surfaces.
• When lightning
strikes, energy is
released.
• This causes the air to
expand rapidly and
send out sound
waves.
Describe what a thunderstorm is
like.
Tornadoes
• A tornado is a small, rotating column of air
that has high wind speeds and low central
pressure and that touches the ground.
• They frequently occur with severe
thunderstorms.
• http://www.youtube.com/user/tornadovideo
sdotnet?blend=1&ob=4
Tornadoes
• Formation:
– Wind traveling in two different directions
causes a layer of air in the middle to begin to
rotate.
– The rotating column of air is turned to a
vertical position by strong updrafts, which
then also begin to rotate.
Tornadoes
– The rotating column of air works its way down
to the bottom of the cloud and forms a funnel
cloud.
– The funnel cloud is called a tornado when it
touches the ground.
What is the air pressure like in a
tornado?
Hurricanes
• A hurricane is a large, rotating tropical
weather system with wind speeds of at
least 119km/h.
• They are the most powerful storms on
Earth.
• It begins as a group of thunderstorms
moving over warm ocean waters.
• http://www.youtube.com/watch?v=_SLXY
RJnYm0
Hurricanes
• Winds traveling in different directions
collide, causing the storm to rotate over an
area of low pressure.
• It turns counterclockwise in the Northern
Hemisphere and clockwise in the Southern
Hemisphere.
• They are fueled by the contact with warm
ocean water.
Hurricanes
• The hurricane continues to grow as long
as it is over its source of warm, moist air.
• It begins to die as it moves over land.
• The eye is the calm, clear center of the
storm.
Why do hurricanes form only over
certain areas?