1. Chapter 17 Section 2
Severe Weather

2. 1. examples of severe weather.
- thunderstorms, hurricanes, tornadoes, blizzards
2. severe weather poses danger to…
- people, structures, and animals
heavy rain, lightning, thunder, and possibly hail
occur in warm, moist air masses and along fronts
begin with warm, moist air being forced up and forming cumulonimbus clouds
rain cools the air which sinks and spreads over the Earth
3. thunderstorm

3. 4. What causes the strong winds in thunderstorms?
- sinking rain cooled air and strong updrafts of warm air
5. damage from thunderstorms
flash flooding in streams- occur with little warning
winds- greater than 89 km/h classified as a severe thunderstorm
hail- dent cars, destroy crops

4. 6. What causes lightning?
warm air is lifted and cool air sinks in clouds which causes parts of a cloud to become oppositely charged
when a current flows between regions of opposite electrical charge, lightning flashes
can occur in a cloud, between clouds, or between a cloud and the ground

5. 7. What causes thunder?
lightning heats the air around it to temperatures of about 30,000°C
heated air expands rapidly then cools quickly and contracts
rapid movement of the molecules forms sound waves heard as thunder
8. tornado
- a violently rotating column of air in contact with the ground
9. wind shear
- the difference in wind speed and direction during thunderstorms

6. 10. How is a tornado formed?
wind shear creates a rotating column of air parallel to the ground
a thunderstorms updraft can tilt the column upward and create a funnel cloud
if the funnel cloud touches Earth it is a tornado
winds can rip apart buildings and uproot trees
can lift animals and houses into the air
winds can blow through open windows and blow off roof and blow out walls
11. damage caused by tornadoes

7. 1. hurricane
most powerful storm
large, swirling low pressure system that forms over the warm Atlantic Ocean
turns heat energy from the ocean into wind
winds of at least 119 km/h
2. typhoons
- storms like hurricanes that form in the Pacific Ocean
3. cyclones
- storms like hurricanes that form in the Indian Ocean

8. 4. How do hurricanes form?
low pressure system forms in Atlantic or Pacific Ocean
winds in northern hemisphere rotate counterclockwise
pushed by surface winds west
gain strength from heat and moisture of warm ocean water
5. damage caused by hurricanes
flooding
destroy crops, demolish buildings, and kill people and animals
heavy winds, high waves

9. winds 56 km/h
temperature is low
visibility is less than 400 m
snow or blowing snow lasting for 3 or more hours
6. blizzard
7. When is a severe weather watch issued?
- when conditions are favorable for severe thunderstorms, tornadoes, floods, blizzards, and hurricanes
8. When is a severe weather warning issued?
- when severe weather conditions already exist

10. 9. What should you do during a severe thunderstorm or tornado?
- take shelter in a basement or middle room away from windows
10. What should you do during a blizzard?
- stay indoors