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Cloud Formation
I. Cloud Formation
A. Cloud-
A collection of millions of tiny water drops in
the air.
B. Why are there clouds in the sky?
1. Clouds start to form when a parcel of warm
moist air starts to rise.
2. Parcel-
A small contained area of air.
3. As the parcel gets higher it cools and
expands.
4. Cold air cant hold as much H2O as warm air.
5. The parcel will reach saturation eventually.
6. If the parcel of air reaches saturation, H2O
will condense onto any solid object. (Dust, salt,
smoke, etc.)
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7. If the parcel is allowed to keep on rising
millions of H2O drops condense onto this stuff.
8. That is when a cloud is formed.
II. Why do clouds form in certain areas?
A. Air can be stable or unstable.
1. Stable Air-
When a rising parcel of air becomes cooler than
the air around it. .
A.) High Pressure
B.) If the air becomes stable it will sink.
C.) If that happens before the air is saturated,
a cloud will not form.
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2. Unstable Air-
When a parcel of air is warmer than the air
around it.
A.) Low Pressure
B.) If the air stays unstable it will continue to
rise.
C.) If it reaches the saturation level it will
form a cloud.
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III. Cloud Classification
A. There are three main types of clouds.
1. Cirrus
A.) Thin feather like clouds.
B.) High altitude.
C.) No precipitation.
D.) Can be a clue that a storm is approaching.
2. Cumulus
A.) Thick puffy clouds.
B.) Some are cauliflower shaped.
C.) Thunderstorms and hail are come in some
types.
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3. Stratus
A.) Light gray, thin layered clouds.
B.) Low altitude.
C.) Light precipitation in most types.
D.) Fog is an example.
B. Cloud Types
1. There are five words that can be attached to
the main cloud types, to give them a more
specific name.
A.) Cirro-
High altitude clouds.
B.) Alto-
Mid altitude clouds.
C.) Strato-
Low altitude clouds.
D.) Nimbo Nimbus-
Very dark heavy rain clouds.
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C. Examples
1. Cumulonimbus
A.) Cumulus cloud that grew into a very large,
dark, heavy rain cloud.
B.) This type of cloud is the heaviest rainmaker.

C.) Thunderstorms, and tornadoes are common.
2. Nimbostratus
A.) Huge layers of dark., low altitude, rain
clouds.
B. ) Very long periods of rain can fall from
these clouds.
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I. High Clouds
1. Cirrus
2. Cirrostratus
3. Cirrocumulus
II. Middle Clouds
1. Altostratus
2. Altocumulus
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III. Low Clouds
1. Stratus
2. Stratocumulus
3. Nimbostratus
IV. Clouds with vertical development
1. Cumulus
2. Cumulonimbus
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IV. Precipitation
A. There are 5 types of precipitation.
1. Rain-
Drops of H2O falling into areas of above freezing
temps..
2. Snow-
H2O that falls as a frozen six sided, flake.
3. Sleet-
Forms when snow falls through a warm area of air,
melts, then freezes back into an ice pellet.
4. Hail-
Warm weather falling lumps of ice.
A.) Most commonly found in cumulonimbus clouds. .

B.) Water freezes in the upper level of the
cloud, into a small ice pellet.
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C. ) When it falls it gets caught in the strong
up drafts of wind.
D.) The up drafts blow the ice pellet back into
the freezing temperatures.
E.) Another layer of ice forms around it.
F.) The process continues until the ice pellets
are too heavy for the up drafts.
G If the ice pellet does not melt before it hits
the ground you will see hail.
5. Freezing rain-
Rain drops that are super cooled.
A.) Salt dissolved in rain lowers the freezing
point of H2O.
B.) As soon as it touches a solid surface it
freezes to it .
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Weather Patterns
I. What causes our weather to change?
A. The movement of different air masses causes
weather to change.
Large body of air that has the same
characteristics as the same area it formed over.

1. Air Mass-
B. There are four basic air massed that effect
weather in United States.
1. Continental Polar (cP)-
Form over cold dry areas.
A.) cP air masses bring clear skies, and cold
temperatures.
B.) Come from Canada.
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2. Continental Tropical (cT)-
Form over warm dry areas.
A.) cT air masses bring clear skies and warm
temperatures.
B.) Come from Mexico.
3. Maritime Polar (mP)-
Form over cold wet areas.
A.) mP air masses bring cloudy skies and cold
temperatures.
B.) Come from the Northern Pacific, or the
Northern Atlantic.
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4.Maritime Tropical (mT)-
Form over warm moist areas.
A.) mT air masses bring cloudy skies and warm
temperatures.
B.) Come form the Gulf of Mexico.
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Blues cold/dry
Green cold/moist
Pink hot/moist
Red hot/dry
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C. Why do air masses change weather?
1. These four air mass types can be either stable
or unstable.
2. When two different air masses collide weather
changes may occur.
3. The boundary between the two air masses is
called a front.
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II. Fronts
A. What are fronts?
1. Front-
The boundary between two different air masses.
2. If air between the boundaries is unstable then
clouds will form and a storm may occur.
B. There are four types of fronts
1. Warm Front-
Happens when a warm air mass moves into a cold
air mass.
A.) The warm air will rise over the cold air
slowly.
B.) If the air is wet, clouds of the stratus and
cumulus variety will form.
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C.) If the air is dry it will bring nice weather
with some high cirrus clouds.
D.) On a weather map they look like this
Cold Air
Warm Air
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2. Cold Front-
Happens when a cold air mass moves into a warm
air mass.
A.) The cold air forces the warm air to rise
quickly.
B.) Makes the air rise twice as fast as warm
fronts.
C.) This rapid movement can cuse large rain
clouds if the air is wet. .
D.) Large cumulus and nimbostratus clouds are
common.
E.) On a weather map they look like this.
Cold Air
Warm Air
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3. Occluded Front-
Happen when two cold air masses collide and force
a warm air mass between them to rise.
A.) Very heavy rain will occur if the air mass is
wet enough.
B.) Cumulonimbus clouds and high winds are
common.
C.) This is the severe weather front.
D.) If air is dry high winds and moderate rain
clouds are still common.
E.) On a weather map they look like this

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Happens when pressure differences cause a warm
front and a cold front to stop moving towards
each other.
4. Stationary Front-
A.) This type of front may stay in the same area
for days.
B.) If the air is wet, light precipitation and
wind can last for as long as the front is
stationary.
C.) Nimbostratus clouds are common.
D. ) If the air is dry light winds and stratus
clouds are common.
E.) On a weather map they look like this

Warm Air
Cold Air
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Severe Weather
V. Severe Weather Storms

A. Thunderstorms

1. Thunder Storms occur when warm, moist air
moves upward rapidly, cools, condenses
and forms cumulonimbus clouds.
2. These clouds are formed from strong updrafts
caused by rapidly rising air.
3. As water drops become to heavy, they start to
fall toward the ground.
4. The falling water causes strong downdrafts of
wind.
5. The rapid updrafts downdrafts build up
electrical charges in the clouds.
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B. What causes thunder and lightning?
1. Opposite charges attract.
2. Like charges repel.
3. When a positively charged cloud passes a
negatively charged area on the ground, particles
from the ground are attracted to the opposite
charge in the sky and current flows between
them.
4. This is a lightning bolt.
5. Thunder results from the rapid heating of the
air around the lightning bolt.
6. Lightning can reach temperatures of 30,000
degrees C.
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7. This extreme heat causes the air around
lightning to expand rapidly.
8. After the lightning is gone the air cools and
contracts.
9. This rapid motion of air particles cause
sound waves called thunder.
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C. Facts about thunder lightning
1. Lightning travels at the speed of light, so
it is seen almost instantly. (300,000 km/s,
186,000 m/s)
2. Thunder travels at the speed of sound, so it
takes longer to hear it. (1000 ft/s)
a.) 1 mile approx. 5 seconds after lightning
you will hear the thunder.
b.) 1 km approx. 3 seconds after lightning
you will hear the thunder.
3. Causes an average of about 200 deaths per
year.
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Severe Weather II
VI. Tornadoes
1. It is a violent funnel shaped wind storm that
moves in a narrow path across land.
A. What causes tornadoes to form?
1. In very severe thunderstorms, the wind at
different heights, blow in different directions,
at different speeds.
the difference in wind direction and wind speed.
2. Wind Shear-
3. Strong updrafts tilt the wind shear and
produce rotation inside of the thunderstorm.
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4. This is when the funnel cloud starts to
appear.
5. When it reaches Earths surface, they are
called tornadoes.
B. Facts about tornadoes
1. Internal winds can reach up to 500 km/hr or
300 mph.
2. Paths of tornadoes are irregular. The path
can change at any time.
3. Width of a tornado can be from 100 meters
wide to 600 meters wide. (Largest are about ½ -1
mile wide.)
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4. Life span is usually less than one hour. (15
minutes on average)
5. Usually occur in the southwest corner of a
low pressure system.
6. 3 out of every 4 tornadoes in the world occur
in an area called Tornado Alley.
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C. Tornado Classification
1. We use the Fujita Scale to classify
tornadoes.
F0 lt 72 mph winds
F1 72-112 mph winds
F2 113-157 mph winds
F3 158-206 mph winds
F4 207-260 mph winds
F5 gt 260 mph winds
2. Winds cant be measured.
3. Damage is assessed to find the wind speeds.

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VII. Hurricanes
A. What is a Hurricane?
1. A Hurricane is a very intense tropical
low- pressure system that has winds of 74 mph
(120km/hr) or more.
B. What causes the hurricane to form?
1. Wind from the southeast trade winds meet
winds form the northeast trade winds.
2. These winds start to spin counterclockwise.
3. A low-pressure system forms in the middle of
the spin
4. Air sinks in the center of this system.
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5. Outside of the center, warm moist air rises
and forms clouds.
6. The center of the hurricane is called the eye
of the storm. (high pressure)
7. Outside the eye is an area called the eye
wall. (low pressure, most intense area of the
storm)
8. When winds reach 74 mph, 120 km/h the storm
is called a hurricane.
C. Facts about hurricanes
1. They get their energy from the heat of the
water.
2. Hurricanes weaken when they reach land or
cold water.
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3. Wind speeds can reach 200 mph in the eye
wall.
4. Most damage is not done by high winds or
rain.
5. Storm Surge causes the most damage.
a.) can raise high tide 20-30 feet.
b.) Causes extensive flooding.
c.) Drowning deaths.
d.) Building damage.
D. Hurricane Names
1. Pre 1953 hurricanes were classified only by
date.
2. 1953-1979 only female names were used.
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3. 1979-present alternating male and female
names are used
4. Names are recycled every six years.
5. Names of the strongest storms are retired
from use.
6. A name is given to the storm after winds
reach 65 mph.
7. A group of people develop a list to use each
year.
8. The list is in alphabetical order. The first
storm name starts with A.
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VIII. Blizzards
A. What is a blizzard?
1. A snow storm that meets all of the following
conditions is considered a blizzard.
Wind speeds over 50 mph.
Whiteout condition snow. (1/4 mile
visibility.)
Below freezing temperatures. (27 F. or
lower.)