Name: ___________________________________________________ Date: 11/16/15 Period: _____ NOTES
Notes: Atmosphere 3.1 – Air Masses and Fronts
Air Pressure Review:
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What is an air mass?
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What happens when an
air mass moves?
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What is a front?
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How do fronts affect
weather?
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What are cold fronts?
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What are warm fronts?
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What is a stationary
front?
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Air Pressure: the weight of the air pressing down on Earth’s surface in
an area.
Air pressure decreases when:
o Density decreases
o Altitude increases (gets higher)
o Air gets warmer (because warm = lower density)
o Amount of water vapor in air increases
Air pressure increases when:
o Density increases
o Altitude decreases (gets closer to Earth’s surface)
o Air gets cooler (cold = higher density)
An air mass is a large volume of air with the same weather
(temperature and humidity) throughout.
An air mass can cover many thousands of square kilometers.
The air gradually takes on the characteristics of the land or water
below it.
As an air mass moves, it brings its temperature and moisture to new
locations.
When an air mass moves to a new region, it carries along its
characteristic moisture and temperature.
The weather changes.
Warm and cold air masses don’t mix together, they stay separate from
each other
A front is a boundary between air masses.
The weather near a front can differ from the weather inside the rest of
an air mass.
Different types of fronts produce different patterns of weather.
When a cold, dense air mass pushes warmer air, it produces a cold
front.
When a warm air mass pushes colder air, it produces a warm front.
Cold fronts can move into a region quickly.
Cold fronts often produce tall cumulonimbus clouds and precipitation.
Brief heavy storms are likely.
Strong thunderstorms can develop and form tornadoes.
After the storms, the air is cooler and often very clear.
Triangles show the direction that a cold front moves.
Draw the cold front symbol:
Warm fronts move more slowly than cold fronts.
Warm air moves gradually up and over a mass of denser and colder
air.
Moisture in the warm air condenses all along the sloping front,
producing cloud-covered skies.
As a warm front approaches, you may first see high cirrus clouds,
then high stratus clouds, then lower and lower stratus clouds.
Often, a warm front brings many hours of steady rain or snow.
After the front passes, the air is usually warmer.
Semicircles show the direction that a warm front moves.
Draw the warm front symbol:
Stationary fronts occur when air masses first meet or when a cold or
warm front stops moving.
For a while, the boundary between the air masses stays in the same
location – it stays stationary.
The air along the front can still move sideways or upward.
The upward air motion may produce clouds that cover the sky,
sometimes for days at a time. (This can produce severe flooding.)
When the front starts moving, it becomes a warm front if the warm air
advances and pushes the cold air.
What are high pressure
systems?
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Alternating triangles and semicircles show a stationary front.
Draw a stationary front symbol:
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At a high-pressure center, air sinks slowly down. As the air nears the
ground, it spreads out toward areas of lower pressure.
In the Northern Hemisphere, the Coriolis effect makes the air turn
clockwise as it moves outward.
A high-pressure system is formed when air moves all the way around a
high-pressure center.
A high-pressure system generally brings clear skies and calm air or
gentle breezes.
A low-pressure system is a large weather system that surrounds a
center of low pressure.
It begins as air moves around and inward toward the lowest pressure
and then up to higher altitudes.
The rising air produces stormy weather.
In the Northern Hemisphere, the air in a low-pressure system circles in
a counterclockwise direction.
Cold fronts go with high pressure systems and thunderstorms.
Warm fronts go with low pressure systems.
Weather is caused by differences in temperature and pressure.
Low pressure is associated with storms (including tornadoes and
hurricanes).
High pressure is associated with clear and dry conditions (good
weather).
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What are low pressure
systems?
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How are fronts and
pressure related?
Summary:
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Questions:
1. What is an air mass?
2. How do air masses changes the weather?
3. What’s the difference between a cold front and a warm front?
4. What kind of clouds form with cold fronts?
5. What kind of weather is associated with cold fronts?
6. What kind of clouds form with warm fronts?
7. What kind of weather is associated with warm fronts?
8. What direction can stationary fronts move?
9. What kind of weather is associated with a high pressure system?
10. What kind of weather is associated with a low pressure system?