Tiny particles in the air called hygroscopic nuclei can cause water vapor to condense and form clouds. Clouds are classified by their appearance and altitude into low, middle, and high clouds. Low clouds include stratus, nimbostratus, and stratocumulus and form near the surface. Middle clouds such as altocumulus and altostratus form between 7,000 to 20,000 feet. High clouds like cirrus, cirrostratus, and cirrocumulus are made of ice crystals and form above 20,000 feet. Different cloud types can indicate upcoming weather conditions.

1. CHAPTER 2
CLOUDS AND FOG

2. Tiny particles of dust, pollen from plants,
factory smoke, and salt particles from
oceans are always present in the air. These
fragments are called hygroscopic nuclei.

3. Tiny particles that absorb or attract
moisture from the air
Hygroscopic Nuclei

4. Clouds form when:
• Water vapor rises
• Vapor condenses
• Droplets cling to hygroscopic nuclei
• Nuclei bunch together and form clouds
or fog

5. Three things may happen to the water
droplets:
• Reevaporate and rise
• Rise and freeze into ice crystals
• Collide with other nuclei and form
larger drops

6. Cloud formations give clues concerning
the forces at work in our atmosphere.

7. Fragments of matter that are always in
the air are called _________ nuclei.
a. hydroscopic
b. hygroscopic
c. psychroscopic
d. psychrodropic

8. Cirrus Stratus
Cumulus
There are three
basic cloud types.

9. A cloud of a class characterized by
thin white filaments or narrow bands
and a composition of ice crystals: of
high altitude, about 20,000 - 40,000
feet
Cirrus

10. A cloud of a class characterized by
dense individual elements in the form
of puffs, mounds, or towers, with flat
bases and tops that often resemble
cauliflower
Cumulus

11. A cloud of a class characterized by a
gray, horizontal layer with a uniform
base, found at a lower altitude than
altostratus, usually below 8,000 feet
Stratus

12. There are also other types of clouds
having names with combinations of
the following:
• Nimbus - rain
• Alto - high
• Fracto - fragmented or windblown

13. Clouds are sometimes classified by
altitudes at which they most frequently
occur:
• Low - surface - 7,000 feet
• Middle - 7,000 - 20,000 feet
• High - above 20,000 feet
• Towering - exceptionally high cloud
with its base in low-altitude

14. There are ten general types of clouds
grouped into low, middle, and high
categories.

15. Low Clouds
Stratus
Nimbostratus
Stratocumulus
Cumulus
Cumulonimbus

16. • Lowest cloud type
• Gray layer with uniform base
• May cause drizzle, but never rain
• Fog becomes stratus when it lifts
Stratus

17. • Dark, shapeless, rain-laden
• Often have streaks of rain extending
to ground
• Often seen in summer at base of
thunderheads
• Brings steady, heavy snow in winter
Nimbostratus

18. A cloud of a class characterized
by a formless layer that is almost
uniformly dark gray, a rain cloud
of the larger type, of low altitude,
usually below 8,000 feet
Nimbostratus

19. Stratocumulus
• Irregular, rounded masses spread out
in puffy or rolling layers
• Usually gray with darker spots
• Do not produce rain
• Usually precede bad weather

20. A cloud of a class characterized
by large dark, rounded masses,
usually in groups, lines, or
waves, the individual elements
being larger than those in
altocumulus and the whole being
at a lower altitude, usually below
8,000 feet
Stratocumulus

21. Cumulus
• Dense, puffy clouds with a beautiful,
cauliflower-like appearance
• They rise by day and disappear at night
• Fleecy cumulus clouds usually mean
fair weather ahead

22. • Dense clouds of the towering variety
• The base is a dark nimbus rain cloud
• May produce severe thunderstorms
and tornadoes
Cumulonimbus
(Thunderheads)

23. A cloud of a class indicative of
thunderstorm conditions,
characterized by large, dense
towers that may reach altitudes
of 75,000 feet, uniform except
for the tops, which appear
fibrous because of the
presence of ice crystals
Cumulonimbus

24. The upper portion of a cumulus
cloud characterized by dense,
sharply defined cauliflower-like
upper parts and sometimes of
great verticality
Thunderhead

25. Middle Clouds
Altocumulus
Altostratus

26. Altocumulus
• Gray or whitish layers, puffy, fleecy
• Made up of water droplets
• Sometimes produce a pale blue or
yellow corona
• Presence means rain is probable
within 24 hours

27. A cloud of a class characterized by
globular masses or rolls in layers or
patches, the individual elements
being larger and darker than those of
cirrocumulus and smaller than those
of stratocumulus: of medium
altitude, about 8,000 - 20,000 feet
Altocumulus

28. Altostratus
• Dense sheets of gray or blue
• Sun or Moon will show through but
without corona
• Light rain is likely within 24 hours

29. A cloud of a class characterized
by a generally uniform gray sheet
or layer, lighter in color than
nimbostratus and darker than
cirrostratus: of medium altitude,
about 8,000 - 20,000 feet
Altostratus

30. High Clouds
Cirrus
Cirrostratus
Cirrocumulus

31. Cirrus
• Thin, wispy, made up of ice crystals
• Called “mare’s tails”
• If scattered, indicate clear, cold
weather
• If in parallel lines, indicate violent
change in weather within 36 hours

32. Cirrostratus
• May nearly cover the sky with a filmy
cloud
• Curly appearance at their edges
• Form large halos around the Sun and
Moon
• Indicate clear and cold weather

33. A cloud of a class characterized
by a composition of ice crystals
and often by the production of
halo phenomena and appearing as
a whitish and usually somewhat
fibrous veil, often covering the
whole sky and sometimes so thin
as to be hardly discernible: of high
altitude, 20,000 - 40,000 feet
Cirrostratus

34. Cirrocumulus
• Thin, patchy clouds that sometimes
form in wavelike patterns
• Do not leave shadows
• Precipitation usually follows within
24 hours

35. A cloud of a class characterized
by thin, white patches, each of
which is composed of very small
granules or ripples: of high
altitude, 20,000 - 40,000 feet
Cirrocumulus

36. Clouds have been leading lost seamen,
navigators, and explorers to land since
the days of the earliest hardy sea
voyagers.

37. Stationary clouds on the horizon usually
indicate an island is close by.

38. In the tropics, clouds often reflect the
colors of the sandy beaches or coral
reefs below.

39. Precipitation (rain, snow, sleet, and hail)
cannot occur without clouds.

40. Temperature and presence of
hygroscopic nuclei or ice crystals
determine if there will be precipitation
and in what form it will take.

41. Raindrops form when moist air is
cooled to the point where the moisture
condenses into heavy drops.

42. Cloud moisture
droplets are
1/2,500 of an inch in
diameter. If the
droplet grows to
1/125 of an inch, it
will fall from the
cloud. The
combining of
moisture droplets is
called coalescence.
Large Raindrop
Small Raindrop
Not to Scale

43. To grow together into one body
Coalescence

44. Coalescence occurs in two known ways:
• Bigger droplets move about slowly,
bump into other droplets and combine
with them (low clouds).

45. Coalescence occurs in two known ways:
• Ice crystals and water droplets form
near each other, the droplets evaporate
and resulting vapor collides with ice
crystals and condenses into snow or
ice pellets. They melt into rain as they
pass through warmer air at lower
altitudes.

46. Rainmaking has been a concern of
humans since the most ancient times.

47. Rain dances, sacrifices, drums, cannons,
and smoke have all been used in an attempt
to make rain, especially during a drought.

48. Seeding a large cumulus cloud with one
pound of artificial nuclei made of dry-ice
or silver-iodide crystals can start a
shower.

49. Seeding can cause:
• Rain to fall sooner
• More rain to fall
• Rain to fall from a cloud that normally
would not produce rain

50. Seeding cannot cause:
• Rain to fall from fair skies or
fair-weather cumulus clouds
• Rain to fall over a large area

51. Sleet occurs when rain formed in relatively
warm air falls through a layer of freezing air.

52. Hail usually occurs in the summertime. It
begins as raindrops, that updrafts take to
greater heights. They are coated with water
from lower clouds, lifted again and again until
too heavy to be lifted.

53. Most hailstones are smaller than
marbles. Hailstones as large as
baseballs have killed people and
animals.

54. In wintertime, when the upper air is very
cold, water vapor will condense into ice
crystals. Snow is the result.

55. Dew is water vapor that condenses on
objects that have cooled below the
condensation point of the air around them.

56. Frost is similar to dew, but it forms
at temperatures below freezing.

57. A covering of minute ice needles,
formed from the atmosphere at
night upon the ground and other
exposed objects when they have
cooled by radiation below the
dew point, and when the dew
point is below the freezing point
Frost

58. Fog is really a low-lying cloud that is near
or touching the surface of the Earth.

59. Fog formation requires the presence of
moisture, a gentle breeze, and a combination
of warm and cold temperatures.

60. Fog is hazardous to aviation because
it limits both ceiling (height above
ground level of lowest layer of clouds
that cover more than half the sky) and
visibility (distance an object can be
Seen with the unaided eye).

61. Fog at sea is a continual hazard
to safe navigation.

62. Fog at Sea

63. The nautical "Rules of the Road" require
that extra lookouts be stationed aboard
ship in foggy conditions.

64. Fog at sea is frequently formed through a
process known as advection. Fog is likely
to develop when warm air that has passed
over warm water moves to an area of colder
water.

65. The horizontal transport of atmospheric
properties
The horizontal flow of air, water, etc.
Advection

66. When warm moist air comes in contact
with colder water, advection fog forms.

67. Advection fog is the name given to
air-mass fog produced by air in motion,
or to fog formed in one place and
transported by wind to another. It will
usually dissipate when the Sun rises.

68. Every Sailor is aware of the fogs that
blanket the harbors and coastlines
near these areas.
Puget Sound
San Francisco
Los Angeles
San Diego
Newport
New York
Norfolk

69. Steam fog is a type of advection fog
formed by air saturation.

70. A condition in the atmosphere
corresponding to 100 percent
relative humidity
Saturation

71. In the far north, "sea smoke" can be seen
in the late fall or winter when a river or
pond "steams" as frigid air cools the water
until it begins to form ice.

72. Fog caused by cold air flowing over
a body of comparatively warm water,
the vapor condensing in small
convective columns near the water
surface and giving the appearance of
smoke or steam
Sea Smoke

73. The heat that the Earth radiates causes
radiation fog. It forms only at night,
over a land surface. The Sun usually
burns the fog away.

74. Fog produced by the nocturnal
cooling of the surface boundary
layer to a temperature at which
its content of water vapor
condenses
Radiation Fog

75. The movement of cold air masses
causes frontal fog. It is common in
the upper Midwest.

76. A fog caused by the movement of two
dissimilar air masses
Frontal Fog

77. Q.1. What does the term
hygroscopic nuclei mean?
A.1. Particles that readily absorb
moisture

78. A.2. Particles that are present in the
air, such as dust, smoke, and
pollen
Q.2. What are examples of
hygroscopic nuclei?

79. A.3. Raindrops are formed when
moist air is cooled to the point
where the moisture condenses
into heavy drops.
Q.3. How are raindrops formed?

80. A.4. Cirrus, cumulus, and stratus
Q.4. What are the three basic types
of clouds?

81. A.5. Fragmented or wind-blown
Q.5. What does the prefix “fracto”
mean?

82. A.6. Altocumulus clouds
Q.6. What clouds are made of water
droplets, sometimes laid out in
parallel bands?

83. A.7. Changes in the atmospheric
conditions
Q.7. What accounts for the different
shapes and altitudes of clouds?

84. A.8. Cirrus clouds
Q.8. What clouds are often called
“mares’ tails?”

85. A.9. High: above 20,000 ft.
Middle: 7,000 to 20,000 ft.
Low: surface to 7,000 ft.
Q.9. What altitudes are associated
with high, middle, and low
clouds?

86. A.10. According to their appearance
and altitude
Q.10. How are clouds generally
named?

87. A.11. Stratus, nimbostratus, and
stratocumulus
Q.11. What are the main types of
low clouds?

88. A.12. Altocumulus and altostratus
Q.12. What are the main types of
middle clouds?

89. A.13. Cirrus, cirrostratus, and
cirrocumulus
Q.13. What are the main types of
high clouds?

90. A.14. Thunderstorms and
tornadoes
Q.14. What type of weather is
associated with
cumulonimbus clouds?

91. Q.15. What weather condition
follows cirrocumulus
clouds?

92. Q.15. What weather condition
follows cirrocumulus
clouds?
A.15. Precipitation