Chapter 16 Section 3:
Severe Weather
Thunderstorms:
Weather changes from day to day. These changes result from the continual shifting of air masses (large
bodies of air having the same moisture and temperature properties as the area they come from). Sometimes severe
weather will develop along the front or leading edges of those air masses.
Thunderstorms are small, intense weather systems that produce strong winds, heavy rain, lightning, and
thunder. Thunderstorms usually occur along the leading edges of cold air masses or cold fronts. Thunderstorms
occur when warm, moist air rises rapidly. When the cooling nears the dew point temperature, cumulus clouds
develop. With further rising dark, cumulonimbus clouds form, and severe weather can result. Severe thunderstorms
produce high winds, hail, and even tornadoes.
Thunderstorms are very active electrically.
Lightning is a large electrical discharge that occurs
between two oppositely charged surfaces or areas.
Lightning within a cloud is most common, but strikes
also occur between clouds, and from clouds to the
ground.
Lightning occurs with all thunderstorms. When
lightning strikes, energy is released. This energy causes
the air around the bolt of light to rapidly expand and
send out shock waves. Thunder is the sound we hear
from the rapid expansion of air along a lightning strike.
Tornadoes:
Tornadoes are produced in about 1% of all thunderstorms. A tornado is a small, violent, rotating column of
air that has high wind speeds and touches the ground. About 75% of the world’s tornadoes occur in the U.S., the
majority in the spring and early summer, and frequent
the midwestern part of the country. Wind speeds can
get to 300 mph, but average between 75 and 110 mph.
The spinning winds can cut a path of total destruction 5
miles long and 100 yards wide.
Tornadoes are produced when winds traveling is
two different directions cause a layer of air in between
to rotate like a roll of toilet paper. Next, the rotating
cylinder of air is turned upright into a vertical position
by strong updrafts of air within the cumulonimbus
cloud. Afterwards, the rotating column works its way
down to the bottom of the cumulonimbus cloud and
forms a funnel cloud. Finally, the funnel cloud is called
a tornado when it touches the ground.
Hurricanes:
A hurricane is a large, rotating tropical weather system with wind speeds from at least 74 mph to over 180
mph. Hurricanes are the most powerful storms on Earth because they cover vast areas of land, sometimes ranging in
size from 100-900 miles across. They are identified differently in other parts of the world, typhoons in the western
Pacific, and cyclones over the Indian Ocean. In the 1950’s, meteorologists began assigning them names.
Hurricanes generally form over the warm, tropical oceans between 5o and 20o north and south latitude. They
begin as a group of thunderstorms moving over tropical ocean waters. Winds traveling in two different directions
collide, causing the storm to rotate. Because the Coriolis Effect, storms rotate ccw in the northern hemisphere, and
cw in the southern hemisphere.
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Hurricanes get their energy from the condensation of water vapor. Once formed, they are fueled through
contact with the warm ocean water. Moisture is added by evaporation. As the warm, moist air rises, the water vapor
condenses, releasing large amounts of energy. They continue to grow as long as they are over warm water. As they
move over cold water or over land, they die off.
At the center of a hurricane is the eye. The air in the
eye is calm. As the eye passes over, a small circle of clear sky
may be visible overhead for a short period of time. This lull
Eye
ends when torrential rains again fall around the outside of the
Updrafts
Downdrafts
eye, and winds rage, drawn in from hot air spiraling up the wall
of the eye. The eye wall is the strongest part of the hurricane.
Hurricane winds can knock down trees and buildings.
They can also cause coastal flooding from on-shore ocean tidal
surges and heavy rains.
Rainbands
Eyewall
Questions Section 16-3: Answer the following questions searching the reading assignment above.
__________1. The leading edge of an air mass is called the ___ .
__________2. Small, intense weather systems that produce strong winds, rain, lightning, and thunder are ____ .
__________3. Large bodies of air with similar temperature and moisture levels as the area they come from are __.
__________4. A large electrical discharge that occurs between two oppositely charged surfaces or areas is ____.
__________5. Lightning occurs with all _____ .
__________6. When lightning strikes, ____ is released.
__________7. The sound we hear from the rapid expansion of air along a lightning strike is called ____.
__________8. A ____ is a small, violent, rotating column of air that has high wind speeds and touches the ground.
__________9. A rotating column of air that works its way down to the bottom of the cumulonimbus cloud is a ___.
__________10. About ___% of the world’s tornadoes occur in the U.S.
__________11. A ____ is a large, rotating tropical weather system with wind speeds of at least 74 mph.
__________12. The most powerful storm on Earth is the ____ because it covers such a large area.
__________13. Hurricanes generally form over a warm, tropical ____ .
__________14. At the center of a hurricane is the ___ .
__________15. Hurricanes get their energy from the ____ of water vapor.
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