1. Chapter 12 Section 9 What causes severe storms?
Objective:
Identify three kinds of severe storms

2. Key Terms
thunderstorm: storm with thunder, lightening, and often heavy rain and strong winds
tornado: small, very violent, funnel-shaped cloud that spins
hurricane: tropical storm with very strong winds

3. Thunderstorms
Usually occur in summer, when a cold front forces warm, moist air to rise rapidly
Cumulus clouds build up to form cumulonimbus clouds
from these, heavy rain or hail falls

4. Thunderstorms Lightning occurs when a cloud discharges electricity
the current causes the air to heat and expand explosively
it creates a wave of compressed air
the wave produces the boom you hear as thunder.
you see lightning flash before you hear thunder because light travels faster than sound

5. DESCRIBE:
What is a thunderstorm like?

6. Tornadoes cause very small, but very violent, storms
frequently occur with severe thunderstorms
waterspouts: tornadoes that form over water
form mostly during the spring or in early summer

7. Tornadoes scientist are not sure how they form
they do know that a storm cloud may develop a small, spinning funnel that reaches down to the ground
the funnel has very low air pressure
when it touches ground, it acts like a giant vacuum cleaner, sucking everything up

8. 2. DESCRIBE:
What is a tornado?

9. Hurricanes The winds spiral towards the center.
may be stronger than 300km/h
From an airplane, the hurricane looks like bands of spinning clouds.
the rain is heavy
wind grows stronger and more destructive the closer you get to the eye of the storm.
The eye is the calm, clear center of the storm
After the eye passes, the winds change direction

10. 3. DESCRIBE:
What is the eye of the hurricane like?

11. 12-9 Classwork When do thunderstorms usually happen?
What causes thunder?
What is the air pressure like in a tornado?
In what seasons do tornadoes usually form?
INFER: Not all of the houses on a block may be damaged by a tornado. How can this be?
CLASSIFY: Which type of severe storm has each of these features? a. thunder and lightning b. funnel- shaped cloud c. giant cumulus clouds d. calm eye e. low air pressure