Transcript Notes

“Cloud Formation”
I. Cloud Formation:
A. Cloud- A collection of millions of tiny water drops in the
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 can’t 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.)
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.
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
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.
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.
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
I. High Clouds:
1. Cirrus
2. Cirrostratus
3. Cirrocumulus
II. Middle Clouds:
1. Altostratus
2. Altocumulus
III. Low Clouds
1. Stratus
2. Stratocumulus
3. Nimbostratus
IV. Clouds with
vertical development:
1. Cumulus
2. Cumulonimbus
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.
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
B.) As soon as it touches a solid surface it freezes to it
“Weather Patterns”
I. What causes our weather to change?:
A. The movement of different air masses causes weather to
1. Air Mass- Large body of air that has the same
characteristics as the same area it formed
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
B.) Come from Canada.
2. Continental Tropical (cT)- Form over warm dry areas.
A.) cT air masses bring clear skies and warm
B.) Come from Mexico.
3. Maritime Polar (mP)-
Form over cold wet areas.
A.) mP air masses bring cloudy skies and cold
B.) Come from the Northern Pacific, or the Northern
4.Maritime Tropical (mT)- Form over warm moist areas.
A.) mT air masses bring cloudy skies and warm
B.) Come form the Gulf of Mexico.
C. Why do air masses change
1. These four air mass types can be either stable or
2. When two different air masses collide weather
changes may occur.
3. The boundary between the two air masses is called a
II. Fronts:
A. What are fronts?
1. Front- The boundary between two different air
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.
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:
Warm Air
Cold Air
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
E.) On a weather map they look like this:.
Cold Air
Warm Air
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
B.) Cumulonimbus clouds and high winds are
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:
4. Stationary Front- Happens when pressure differences
cause a warm front and a cold front
to stop moving towards each other.
A.) This type of front may stay in the same area for
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
E.) On a weather map they look like this:
Warm Air
Cold Air
“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
5. The rapid updrafts & downdrafts build up
electrical charges in the clouds.
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
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.
7. This extreme heat causes the air around
lightning to expand rapidly.
8. After the lightning is gone the air cools and
9. This rapid motion of air particles cause sound
waves called thunder.
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
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
“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.
2. Wind Shear- the difference in wind direction
and wind speed.
3. Strong updrafts tilt the wind shear and produce
rotation inside of the thunderstorm.
4. This is when the funnel cloud starts to appear.
5. When it reaches Earth’s surface, they are called
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.)
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.
C. Tornado Classification:
1. We use the Fujita Scale to classify tornadoes.
< 72 mph winds
72-112 mph winds
113-157 mph winds
158-206 mph winds
207-260 mph winds
> 260 mph winds
2. Winds can’t be measured.
3. Damage is assessed to find the wind speeds.
VII. Hurricanes:
A. What is a Hurricane?
1. A Hurricane is a very intense tropical lowpressure 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.
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
2. Hurricanes weaken when they reach land or
cold water.
3. Wind speeds can reach 200 mph in the eye
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
2. 1953-1979 only female names were used.
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
6. A name is given to the storm after winds reach
65 mph.
7. A group of people develop a list to use each
8. The list is in alphabetical order. The first storm
name starts with A.
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
* Below freezing temperatures. (27 F. or