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/tornadovideosdotnet?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=_SLXYRJnYm0

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?