Download Unit 4 Section 2 Severe Weather Answer Key - WAHS

Name:
Date:
Period:
Unit 4: Earth’s Fluid
Spheres
Section 2: Severe
Weather
Thunderstorms, tornadoes, or floods can happen almost anywhere. In some regions,
these events occur very often, whereas in others they are unusual. However, at some time
in your life you will probably experience some form of severe weather.
In this chapter, you will learn what conditions create thunderstorms.
How and Why Warm Air Rises (F 70)
As air warms, it becomes less dense than its cooler surroundings and rises. Warm air is
less dense than cold air because molecules in warm air are more active than the
molecules in cold air. As molecules move around with increasing speed, the distance
between them gets larger and their density decreases.
Air masses can also be forced to rise when they flow over mountains or collide with other
air masses. There are four main mechanisms that cause air to rise on a regional scale.
1. Convective Uplift – Convection refers to upward and downward motions of air caused by
differences in air temperature (and therefore differences in density). As the Sun warms
the ground, the ground warms the air immediately above it. Cooler, denser air from
above sinks and forces the warmer air upward. The ascending warm air expands and
cools and eventually sinks back to ground, completing the convective circulation.
2. Orographic Uplift – (orographic refers to mountains) When the wind encounters a
mountain range, the mountain range acts as a barrier, and forces the air upward.
3. Frontal Wedging – When a cold air mass meets a warm air mass, the more dense cold
air wedges or forces its way beneath the less dense warm air along a cold front.
4. Convergence – When winds blowing from different directions meet head-to-head, or
converge, they have nowhere to go but up.
Unit 4, Section 2: Severe Weather
1
What is a Front?
A front is a narrow zone of transition between air masses that contrast in temperature
and/or humidity. The map on the next page shows the “source regions” for the air masses
that regularly move over North America. As indicated by the arrows, cold air usually flow
southeastward and warm air masses flow northeastward. As air masses move out of
their original regions, they change depending on the route they travel.
Example: Cold air traveling southward will warm up before it reaches Florida so that is
why Florida never gets as cold in the winter.
Air masses are
classified by their
temperature and
humidity (or moisture
content), as follows…
 Continental:
relatively dry air
masses that form
over land.
 Maritime: relatively
humid air masses
that form over the
ocean.
 Polar: cold air
masses that form
at high latitudes.
(Example: northern
Canada)
 Tropical: warm air
masses that form
at low latitudes.
(Example: Gulf of
Mexico)
General Types of air masses include:
1. continental polar – cold and dry
2. continental tropical – warm and dry
3. maritime polar – cold and humid
4. maritime tropical – warm and humid
5. artic air – exceptionally cold and dry
Unit 4, Section 2: Severe Weather
2
When a front develops, whether it is a cold or warm front is determined by which air mass
retreats or gives way to the other. If the colder (or drier) air advances while the warmer (or
more humid) air retreats, the transition zone is considered a cold front. On the other hand,
if the warm air advances while the cold air gives way, it is considered a warm front.
Example of a cold front.
Development of a Thunderstorm
Thunderstorms can be caused by air rising along either warm fronts or cold fronts.
However, the most intense thunderstorms develop from cold fronts. As a general rule, the
greater the difference in temperature between the air masses, and the more rapidly the
cold-air mass wedges under the warm air mass, the greater the chance a thunderstorm
will form. Another way thunderstorms can form is through local convection of a warm and
humid air mass.
A thunderstorm is a relatively small, short-lived weather system. They usually affect an
area the size of a city and for the duration of about an hour. A thunderstorm completes its
“lifecycle” in three stages: cumulus, mature, and dissipating. The most severe weather
occurs during the mature stage. At any given moment about 1800 thunderstorms are
happening on Earth. This equates to 16 million thunderstorms per year worldwide.
During the first stage, cumulus clouds build upward and laterally with a flat bases and
towering tops. Cumulus clouds develop where air ascends as an updraft. As the air
reaches the higher levels, it expands because the pressure is lower and that makes the air
cool. The water vapor in the air condenses because of the colder temperatures producing
clouds. No precipitation occurs during this stage and sometimes the cumulus clouds do not
produce a thunderstorm.
A thunderstorm that produces severe weather requires a very strong updraft that builds
the developing cumulonimbus (nimbus means rain) cloud to great altitudes. Usually
convection alone is not enough to produce a thunderstorm. Frontal wedging, orographic
Unit 4, Section 2: Severe Weather
3
uplifting, or converging surface winds can strengthen an updraft and cause the cumulus
clouds to build vertically.
When a cumulus cloud gets tall enough, it will produce rain, hail, or even snow. Once the
precipitation begins, the thunderstorm has reached its mature stage. Falling precipitation
causes a downdraft next to the continuing updraft. During the mature stage, precipitation
is the heaviest, lightening is most frequent, and hail or even tornadoes may develop. The
higher the thunderstorm builds, the more severe the weather.
Precipitation and the downdraft eventually spread throughout the thunderstorm as the
system enters its dissipating stage. Precipitation tapers off and ends, clouds dissipate,
and the chances for severe weather decrease dramatically.
Review Questions
1. What happens as air warms? _______________________________________
___________________________________________________________
2. Why is warm air less dense than cold air? ______________________________
___________________________________________________________
3. What are two things that can force air masses to rise?
a. _________________________________________________________
b. _________________________________________________________
4. Describe what happens during convection. ______________________________
___________________________________________________________
___________________________________________________________
5. What happens when a cold air mass meets a warm air mass?
___________________________________________________________
___________________________________________________________
6. In what direction do warm and cold air masses usually flow?
___________________________________________________________
7. Why are winter temperatures warmer in Florida then they are in the Great Lakes
region?
___________________________________________________________
___________________________________________________________
8. What are air masses classified by?
_____________________________ and __________________________________
Unit 4, Section 2: Severe Weather
4
9. Describe each one of the five air masses.
a. _________________________________________________________
b. _________________________________________________________
c. _________________________________________________________
d. _________________________________________________________
e. _________________________________________________________
10. How does a cold front form? _______________________________________
___________________________________________________________
11. How does a warm front form? ______________________________________
___________________________________________________________
12. What causes a thunderstorm? ____________________________________________
___________________________________________________________
___________________________________________________________
13. With what type of fronts do the most intense thunderstorms form? ________________
14. What are the three stages in the lifecycle of a thunderstorm?
a. ________________
b. _________________
c. _______________
15. During which stage is the weather the most severe? __________________________
16. How do cumulus clouds form and what do they look like?
___________________________________________________________
___________________________________________________________
___________________________________________________________
17. What are thunderstorm clouds called once they produce rain? ___________________
18. What causes cumulus clouds to build into high altitude thunderstorm clouds?
___________________________________________________________
___________________________________________________________
19. What event signals the beginning of the mature stage?_________________________
20. What is the relationship between the height of a thunderstorm and the weather it
produces?
___________________________________________________________
___________________________________________________________
___________________________________________________________
Unit 4, Section 2: Severe Weather
5
Name:
Date:
Period:
How Clouds Form (F 80)
All air contains water vapor, which is water that exists in the atmosphere as an invisible
gas. Water vapor is not the same as clouds, fog, or steam, which is composed of tiny,
visible droplets of water suspended in the air. There is a limit to how much water vapor
can be concentrated in the air and when that limit is reached, the air is considered
saturated.
Warm air can hold more water vapor than cold air. When air is saturated with water vapor,
some water vapor condenses into tiny droplets of water (or, if the temperature is really
low, tiny ice crystals) that are visible in the form of clouds. The most common way clouds
develop is by cooling of the air as it rises in the atmosphere.
Ascending air cools because of expansion. A gas cools when it expands. Air coming out
of a tire is cool because it is expanding as it escapes. The pressure is much less on the
outside than on the inside the tire.
Air Pressure
Air pressure is the cumulative force of a multitude of air molecules colliding with a unit
surface area of any object in contact with air. Think about a column of air pushing down
on a specific surface area at the base of the column. Air pressure decreases with altitude,
because the mass of air above you is getting smaller.
Air that rises, like in an updraft, expands as it rises and loses heat. With that cooling, the
air becomes saturated and excess water vapor condenses into droplets, which form
clouds. This happens in the updraft of a thunderstorm. Conversely, if air is descending it is
encountering growing air pressure and it warms and becomes compressed. During the
dissipating stage of a thunderstorm the downdraft spreads through the thunderstorm cloud,
and with compressional warming, the cloud vaporizes.
Condensation Nuclei
In addition to saturated air, cloud formation requires surfaces on which the water vapor
can condense. Earth’s atmosphere contains an abundance of tiny solid and liquid
particles that water vapor can condense on. These particles are called condensation
nuclei. Nuclei are products of many different natural and human-related activities.
Unit 4, Section 2: Severe Weather
6
Forest fires, volcanic eruptions, wind erosion of soil, saltwater spray, motor vehicle
exhaust, and various industrial emissions are all sources of nuclei. Nuclei that promotes
condensation is called condensation nuclei and nuclei that promotes the formation of ice
crystals are called ice-forming nuclei.
Types of Clouds
Meteorologists classify clouds into three broad categories based upon shape: cirrus,
stratus, and cumulus. Cirrus clouds are wispy, stratus clouds are layered, and cumulus
clouds are puffy (like cottonballs).
Clouds are further classified by their altitude: high, middle, low, or clouds with vertical
development. And finally, clouds are classified by their composition: water droplets or ice
crystals. Photographs of these clouds can be found on page F 82-83 of your text.
The Mature and Dissipating Stages of a Thunderstorm (F 84)
In the previous lesson, you learned that a
thunderstorm begins when a cumulus cloud
develops in an updraft of air. The more
humid the air, the better chance a
thunderstorm will form. In general, the more
vigorous the updraft, the greater the altitude
to which a thunderstorm cloud builds, and
the more likely that the thundercloud can
build. Consider the four different layers of
the Earth’s atmosphere (listed from lowest to
highest): troposphere, stratosphere,
mesosphere and thermosphere. The
boundaries between these layers are
defined by air temperature.
We live in the troposphere. On average, air
temperature drops with increasing altitude
up to the top boundary of the troposphere which is called the tropopause.
The next layer up is the stratosphere, in which the air temperature is at first constant with
altitude and then increases with altitude. A thunderstorm cloud that pushes above the
tropopause and into the lower part of the stratosphere will be colder and denser than the
surrounding air and will sink back down into the troposphere. Because of this reason,
even a very intense thunderstorm cannot build much higher than the tropopause. This is
also why cumulonimbus clouds develop their characteristic flat top.
Thunderstorm precipitation falls through the updraft, weakening it and eventually dragging
air downward, producing a downdraft alongside the updraft. The downdraft leaves the
Unit 4, Section 2: Severe Weather
7
base of the cloud and flows along the ground ahead of the shaft of precipitation. The
leading edge of this rain-cooled gusty air is like a miniature cold front and is known as a
gust front.
In an intense thunderstorm, a downdraft may strike the ground with wind speeds in excess
of 100 km/hr (60 mph). An intense downdraft is known as a downburst. A downburst
pushes ahead of the thunderstorm and can be strong enough to uproot trees and damage
buildings.
As precipitation
spreads throughout
the thunderstorm
cloud, so does the
downdraft.
Eventually the
downdraft
overpowers the
updraft. The updraft
dies, precipitation
comes to an end,
and the cloud slowly
vaporizes. This is
the final, or
dissipating, stage of
the thunderstorm.
Review Questions
21. What is water vapor? _____________________________________________
___________________________________________________________
22. What does the upper limit of water vapor in the atmosphere depend on?
___________________________________________________________
___________________________________________________________
23. Compare the amount of water vapor in warm and cool air.
___________________________________________________________
___________________________________________________________
24. What happens when air is saturated with water vapor?
___________________________________________________________
___________________________________________________________
25. How do clouds develop in the atmosphere? _________________________________
___________________________________________________________
Unit 4, Section 2: Severe Weather
8
___________________________________________________________
26. What happens to ascending air? __________________________________________
___________________________________________________________
___________________________________________________________
27. What happens to air pressure as altitude increases? ___________________________
28. What happens to descending air?__________________________________________
___________________________________________________________
___________________________________________________________
29. What are the sources of the nuclei?
___________________________________________________________
___________________________________________________________
30. What are the three things that meteorologist use to classify clouds?
a. _______________________________________________________
b. _______________________________________________________
c. _______________________________________________________
31. Describe each one of the three categories of clouds.
a. _______________________________________________________
b. _______________________________________________________
c. _______________________________________________________
32. What are the four layers of the Earth’s atmosphere from lowest to highest?
a. ________________________
c. ________________________
b. ________________________
d. ________________________
33. What defines the boundaries of these four layers?____________________________
___________________________________________________________
___________________________________________________________
34. What is a downburst?___________________________________________________
___________________________________________________________
___________________________________________________________
35. Describe the dissipating stage of a thunderstorm._____________________________
___________________________________________________________
___________________________________________________________
___________________________________________________________
Unit 4, Section 2: Severe Weather
9
How Radar Works (F 90)
Although most thunderstorms last for less than an hour, some can produce severe weather
and damage for several hours such as flash flooding, destructive hail, and tornadoes. In
this chapter, you will learn about radar and how it is used to track storm systems.
36. What is radar an acronym for? ______________________________________
37. Describe how radar works. ________________________________________
___________________________________________________________
___________________________________________________________
___________________________________________________________
___________________________________________________________
38. What type of energy does radar use? _________________________________
39. What is radar echo? ____________________________________________
___________________________________________________________
40. How is echo strength calibrated? ____________________________________
___________________________________________________________
41. Why does the curve of the Earth limit the range of radar? ____________________
___________________________________________________________
___________________________________________________________
42. What is radar’s maximum range? ____________________________________
43. What is ground clutter? __________________________________________
___________________________________________________________
___________________________________________________________
44. What do radar images track? ______________________________________
___________________________________________________________
___________________________________________________________
Unit 4, Section 2: Severe Weather
10
45. How are past positions, storm center movement, and future positions represented on a
radar screen?
___________________________________________________________
___________________________________________________________
___________________________________________________________
46. Why do we sometimes have prolonged periods of severe weather?
___________________________________________________________
___________________________________________________________
47. Where and when are MMC’s most common?
___________________________________________________________
___________________________________________________________
48. How long does a typical MMC last? __________________________________
49. What kind of thunderstorm is responsible for the most powerful tornadoes and the
largest, most destructive hail? ____________________________
Unit 4, Section 2: Severe Weather
11
Name:
Date:
Period:
Severe Weather Hazards: Flash Floods (F 98)
Thunderstorms can produce torrential rains. Usually the rain does not last very long and
cause no serious problems, however, sometimes heavy rains can last for hours. This can
lead to a flash flood.
A flash flood is a sudden rise in the water level of a stream, river, or a man-made drainage
channel in response to extremely heavy rains. Flash floods can also occur when a brief but
heavy rain falls over the entire area of a very small watershed. In some places, water
might overflow stream banks and collect in low-lying places.
The Link Between Flash Floods and Thunderstorms
The life cycle of a thunderstorm cell is typically less than an hour. How could torrential
thunderstorm rains last for many hours? Flooding usually results from more than one
thunderstorm cell. Flooding thunderstorms are most likely in mountainous terrain where a
persistent flow of humid air up a mountain slope can cause thunderstorm cells to develop
and redevelop over and over.
Outside of the mountains, another possible cause of flooding rains is a succession (or
“train”) of slow-moving thunderstorm cells that mature over essentially the same
geographic area. Thunderstorms move slowly when the steering winds in the middle and
upper part of the troposphere are relatively weak.
Watersheds
A river plus all of its tributaries (smaller creeks that feed into the main river) drain a fixed
geographical area, and that area is the drainage basin. Drainage basins are also called
watersheds. Heavy rain falling on the upstream part of the drainage basin might cause
flooding downstream in areas that received no rain. In other words, just because it is not
raining where you are does not necessarily mean there is no flood danger.
Where are flash floods most likely to occur?
Flash floods may be more likely in an urban area than in the surrounding countryside. The
reason for this is the rain in the country can seep into the soil. In the city, rain cannot seep
into asphalt or concrete parking lots, roads, and driveways. Frozen soil is also impervious
Unit 4, Section 2: Severe Weather
12
to water. Instead, the water runs off these surfaces into nearby streams or other drainage
ways. Storm sewers also channel water from roads into streams.
Streams receiving so much water at one time can overflow their banks quickly. Also, storm
sewers sometimes clog or cannot handle excessive volumes of water and back up into the
streets.
The flash flood hazard is particularly serious in mountainous terrain where river valleys are
narrow and deep. Stream level can rise very quickly because there are no broad areas
next to the stream channel where the water can spread out. If the river valley also contains
roads, campgrounds, or houses, a flood can be very destructive.
When a river overflows its banks in a non-mountainous area, excess water spreads over a
broad flat area adjacent to the river known as a floodplain. Floodwaters are usually
shallower then they are in mountain valleys where floodplains are very narrow or
nonexistent. Also, in non-mountainous areas, roads and buildings usually are not located
as close to the river as they might be in the mountains.
Safety Tips for Floods
Flash floods can strike any time and any place with little or no warning. In mountainous or
flat terrain, distant rain may be channeled into gullies and ravines, turning a quiet
streamside campsite into a rampaging torrent in minutes. City streets can become rivers in
seconds. Observe these flash flood safety rules. They could save your life.
 Keep alert for signs of heavy rain such as thunder and lightning, both where you are
and upstream. Watch for rising water levels.
 Know where high ground is and get there quickly is you see or hear rapidly rising
water.
 Don’t pitch your tent in a dry streambed.
 Be especially cautious at night; the danger is harder to recognize then.
 Do not attempt to cross flowing water that may be more than knee deep. If you have
doubts, do not cross.
 Do not try to drive through flooded areas.
 If your vehicle stalls, abandon it and seek higher ground immediately.
 During threatening weather, listen to commercial radio or TV, or NOAA Weather
Radio for weather watch and warning bulletins.
Review Questions
Unit 4, Section 2: Severe Weather
13
50. How long does one thunderstorm cell usually last? ____________________________
51. How do thunderstorms cause flooding?
___________________________________________________________
___________________________________________________________
52. Where are flooding thunderstorms usually found?
___________________________________________________________
___________________________________________________________
53. Why are flash floods more likely in urban areas than in the countryside?
___________________________________________________________
___________________________________________________________
54. Why is it a problem if streams receive too much water at one time?
___________________________________________________________
___________________________________________________________
55. Why are flash flood hazards particularly serious in mountainous terrain?
___________________________________________________________
___________________________________________________________
___________________________________________________________
56. List four safety tips for floods.
a. _________________________________________________________
b. _________________________________________________________
c. _________________________________________________________
d. _________________________________________________________
57. When did the flash flood in the Big Thompson Canyon occur? ___________________
58. What caused the flash flood in the Big Thompson Canyon? _____________________
___________________________________________________________
___________________________________________________________
59. Why did the thunderstorm cells stay in the area? ______________________________
___________________________________________________________
___________________________________________________________
60. How much rain did they receive to cause the flood? ___________________________
61. What happened to people trying to escape in their cars? ________________________
___________________________________________________________
Unit 4, Section 2: Severe Weather
14
62. What floodplain management strategies helped to prevent a greater loss of life during
the 1997 Fort Collins flash flood? __________________________________________
___________________________________________________________
___________________________________________________________
___________________________________________________________
Name:
Date:
Period:
Severe Winds and Tornadoes (F 116)
In the United States about 10,000 severe thunderstorms occur in an average year. About
10% of these produce tornadoes, and perhaps 1% of those tornadoes are violent and
destructive.
Downbursts and Tornadoes
Downbursts that affect a relatively small area (4 km or less across) are known as
microbursts. Microbursts cause sudden changes in wind speed and direction called wind
shear, which can interfere with aircraft flight. Microbursts over short distances are
particularly hazardous to aircraft taking off or landing because these winds typically affect
only a part of the runway and are difficult to detect. Near the ground, downbursts winds
blow outward from a central area, whereas winds produced by a tornado tend to swirl in
circles. Microbursts can be deadly.
Tornadoes threaten people and property mainly because of their exceptionally strong
winds and powerful updrafts. Winds blowing hundreds of kilometers an hour knock over
trees and power poles, toss cars around as if they were toys, and destroy even wellconstructed buildings. Another danger is flying glass and splintered lumber, which causes
much of the injuries associated with tornadoes. In violent tornadoes, the updraft near the
center of the system may top 160 km/hr (100 mph), strong enough to lift a house off its
foundation. The most destructive tornadoes are large systems made up of two or more
whirling masses of air (multi-vortex systems).
The Fujita Scale
Tornadoes intensity is rated on the Fujita scale (or F-scale) devised by the late Professor
T. Theodore Fujita of the University of Chicago. The F-scale is based on rotational wind
speeds estimated from property damage and classifies tornadoes as weak (F-0 or F-1),
strong (F-2 or F-3), or violent (F-4 or F-5).
Characteristics of Tornadoes
Unit 4, Section 2: Severe Weather
15
Tornadoes come in variety of shapes, ranging from cylindrical cloud masses having nearly
uniform lateral dimensions to long, slender rope-like pendants.
Type of
Tornado
Weak
Size of Tornado
(width in meters)
Wind Speed
(km/h)
Distance
Traveled (km)
Life
Expectancy
100 m
< 180 km/hr
< 1.5 km
1-3 min
> 100 m
500 km/hr
160 km +
2 hrs +
Strong (Intense)
Tornado paths are often erratic and produce a hopscotch pattern of destruction as the
alternatively touch down and lift off of the ground. The average forward speed of a tornado
is about 48 km/h (30 mph). Winds in the vast majority of Northern Hemisphere tornadoes
blow in a counterclockwise direction when viewed from above. Strong tornadoes can
occur in mountainous terrain.
Each year, the United States can anticipate between 700 and 1100 tornadoes, with only
about 1% rated as violent. By late February, the maximum tornado frequency is along the
central Gulf states. In April, the maximum frequency shifts to the southeast Atlantic states.
In May and June, the highest is usually over the southern Great Plains, and by early
summer it has shifted to the northern Plains and the Great Lakes region.
Tornado Development
Most tornadoes develop in supercell thunderstorms. In a supercell thunderstorm, a
powerful updraft interacts with horizontal winds to cause air to rotate about a vertical axis.
The rotating air is called a mesocyclone. If conditions are right, the mesocyclone
circulation narrows and grows downward towards Earth’s surface and the wind speed
increases. Example: Ice skater bringing arms in during a spin increases spin speed.
You can see tornadoes because humid air expands and cools as it is drawn inward toward
the low-pressure center of the whirling system. Cooling of the air causes water vapor to
condense into droplets which is what you are able to see. If the funnel cloud strikes the
ground, dust and debris are drawn into its circulation, and the system is described as a
tornado. About 60% of mesocyclones produce tornadoes.
Unit 4, Section 2: Severe Weather
16
Most supercell thunderstorm develop as part of a squall line in the warm, humid air ahead
of a well-defined cold front. A key requirement for bringing contrasting cold and warm air
masses together is a strong cyclone. A cyclone is a stormy weather system that is plotted
on a weather map as L or Low for the relatively low air pressure at its center. Here,
cyclone does not refer to a hurricane or tornado, but rather a large weather system in
which surface winds blow counterclockwise and inward. They can affect up to one third of
the eastern half of the United States at one time.
Where and When are Tornadoes Common?
Although severe thunderstorms are tornadoes have been reported
in every state, they are most frequent in a north-south belt in the
center of the nation, stretching from east Texas northward through
Oklahoma, Kansas, Nebraska, and into southeast South Dakota.
This area is known as “tornado alley.” The frequency of tornadoes
in that region is greater than anywhere else in the world!
Although tornadoes have been reported in every month of the year,
they are most common in spring and early summer. At this time of year, the temperature
contrast in between air masses is greatest, meaning that the potential for severe
thunderstorm development is highest.
Predicting Tornadoes
Tornadoes are hard to predict because
they are such short-lived systems.
When conditions in the atmosphere
appear favorable for the development
of a severe thunderstorm or tornado,
the National Weather Service’s Storm
Prediction Center in Norman,
Oklahoma, issues a severe
thunderstorm or tornado watch. When
Unit 4, Section 2: Severe Weather
17
one has been spotted, the weather service issues an update letting people know what
areas are affected.
The National Weather Service radar uses the Doppler effect to determine how air is
moving within a thunderstorm and can provide the public with advance warning of the
development of tornadoes. The Doppler effect refers to a shift in frequency of sounds
waves or electromagnetic waves when a source is moving. Example: Ambulance sirens
sounds high pitched as they approach then lower as they move away. In this way,
meteorologists can track particles in the atmosphere as they move and detect
mesocyclones before they turn into tornadoes.
Tornado Safety Tips
 If you have been warned of a tornado or see one approaching, take shelter
immediately.
 Tornado shelter should have a steel-frame or a reinforced concrete building. If you are
at home, go into the basement. If there is no basement, go to a small interior room
such as a closet or hallway in the center of the house on the lowest floor.
 Seek shelter under a mattress or a rigid piece of furniture.
 Do not go near windows or outside walls and do not open windows or exterior doors.
 If you are in a large building, go to an interior hallway on the lowest floor. Avoid areas
with wide free-span roofs such as auditoriums and gymnasiums.
 Never try to outrun a tornado in a car. It is hard to predict what direction they are
going.
 Never seek shelter in a mobile home, car, or other motor vehicle.
Review Questions
63. What type of damage can a tornado cause? ________________________________
___________________________________________________________
___________________________________________________________
64. What speed can the updraft in a violent tornado reach? _______________________
65. What is tornado intensity rated on? _______________________________________
66. What is this scale based on? _______________________________________
___________________________________________________________
Unit 4, Section 2: Severe Weather
18
67. What is a weak tornadoes path, life expectancy, and wind speed?
___________________________________________________________
___________________________________________________________
68. What is an intense tornadoes path, life expectancy, and wind speed?
___________________________________________________________
___________________________________________________________
69. In what direction does a tornado usually rotate? _____________________________
70. Why do tornadoes create a “hopscotch” pattern of destruction?
___________________________________________________________
___________________________________________________________
71. What is the average forward speed of a tornado? _____________________________
72. How many tornadoes can the U.S. anticipate every year? ______________________
73. What causes the funnel-shaped cloud that extends down from the parent
cumulonimbus cloud?___________________________________________________
___________________________________________________________
___________________________________________________________
74. Where do most supercell thunderstorms develop?
___________________________________________________________
___________________________________________________________
75. Where are severe thunderstorms and tornadoes most frequent?
___________________________________________________________
___________________________________________________________
76. What is that frequent tornado area called? ___________________________________
77. During what time of year are tornadoes most common and why?
___________________________________________________________
___________________________________________________________
78. Why are tornadoes hard to predict?
___________________________________________________________
___________________________________________________________
79. How does the National Weather Service use the Doppler effect?
___________________________________________________________
___________________________________________________________
Unit 4, Section 2: Severe Weather
19
80. What does the Doppler radar monitor?
___________________________________________________________
___________________________________________________________
81. What are the colors displayed on a Doppler radar and what do they indicate?
___________________________________________________________
___________________________________________________________
___________________________________________________________
82. List three tornado safety tips.
___________________________________________________________
___________________________________________________________
___________________________________________________________
___________________________________________________________
Unit 4, Section 2: Severe Weather
20