Name: ____________________________
Date: _________________________
Mr. Lanik/Ms. Cooley/Mr. Liebowitz
Chapter 20.1-20.2 Notes
Meteorology –
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Air Mass –
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Front _________________________________________________
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Cold Front ___________________________________________________
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Warm Front –
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Occluded Front –
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Stationary Front –
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I – Air Masses
An (1) ___________________________ is a large body of air in the lower troposphere
that has similar characteristics throughout. An air mass can be several thousand kilometers in
diameter and several kilometers high. Two or three air masses can (2) ________________ the
entire United States! Throughout an air mass,
(3) _________________________ and
(4) _______________________________ are nearly uniform (the same).
The temperature and humidity of an air mass depends on where the mass
(5) ________________________. In polar regions the lack of (6) ____________________
causes the ground to be very cold. If an air mass stays in a polar region for a long time, the air
mass becomes cold as well. The opposite happens in tropical regions.
The moisture of an air mass depends on the surface where it came from. If an air mass
stays over land for a long period of time, it becomes (7) ______________, where an air mass
over the ocean (8) _________________ water vapor and becomes (9) ___________________.
When an air mass moves from one place to another, it takes the temperature and humidity
of its place of origin with it. However, some of its characteristics may change as it moves across
the country. When cold polar air moves south, it affects the (10) ______________________ of
the area it enters, as well as slowly (11) ______________________ as it moves across a warmer
(12) _________________________________. Earth’s topography also helps change the
temperature and humidity of an air mass as it travels.
II – Types of Air Masses
There are (13) ________________ main air masses in North America:
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(14) _____________________________________________,
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(15) _____________________________________________,
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(16) _____________________________________________,
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(17) _____________________________________________,
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(18) _____________________________________________.
Continental Arctic (cA) air masses originate in the arctic regions where the air is
extremely cold. Because cold air is incapable of containing much
(19) ________________________, cA air masses are very (20) ______________________.
Continental Polar (cP) air masses start over Alaska and Canada and are somewhat
warmer than the cA air masses. The differences in temperature and humidity between cA and cP
air masses are usually (21) ______________________. When cP air passes over the Great Lakes
region in the late fall when the water is still warm, the cold, dry air picks up moisture from the
lakes, then dumps the precipitation as snow, causing (22) _______________________________.
Maritime polar (mP) air masses form over the ocean in high latitudes. These air masses
are both (23) ____________________ and (24) ______________________. mP air is not as cold
as cP air because of the difference in temperatures between the land and the oceans. Occasionally
mP air from the North Atlantic brings heavy snowstorms called
(25) ______________________________ to the East Coast in the winter and cool, clear weather
to the area in the summer.
Maritime tropical (mT) air masses form over a warm tropical ocean and gain both
warmth and moisture. In the summertime, mT air from the Bahamas and the Gulf of Mexico
moves (26) __________________________ around the high pressure over the Atlantic Ocean,
bringing heat and humidity to the Midwest and Eastern U.S. Since this air mass contains a lot of
moisture, (27) ______________________________________ often develop. As the sun heats
the ground, the moist mT air is heated from below and (28) _____________________, forming
thunderclouds. When the sun sets, the clouds and thunderstorms leave as the surface cools.
Continental tropical (cT) air masses originate over deserts and are hot and dry. Most of
the time a cT air mass originates as a maritime air mass but becomes dry as it passes over
mountains. cT air masses produce massive (29) ______________________________ in most of
the United States. mT air usually produces temperatures no higher than 100 degrees Fahrenheit,
but cT air is much (30) ______________________, with temperatures exceeding 100 degrees
Fahrenheit. cT air is dry and does not bring cloud or thunderstorms, however if this type of air
mass comes into a crop region, it can cause serious damage to them.
III – Fronts
Air masses of different types do not mix easily. The boundary that separates different air
masses are called (31) ________________________. The width of a front can range from 200
meters to 200 kilometers. Fronts can also be as high 5 kilometers and as long as 2000 kilometers
and can effect weather patterns in areas hundreds of kilometers wide. Fronts are most common at
(32) ____________________________________, where southward moving polar air masses and
northern moving tropical air masses often meet.
At the front, the less-dense air mass is forced to (33) _________________________ over
the denser air mass. Because of this the front is usually
(34) ___________________________________.
Fronts usually bring (35) ___________________________________. At the surface of
the front the less-dense air rises into the troposphere where the air cools, and if humid enough,
can create clouds and bring precipitation.
IV – Types of Fronts
The weather associated with a particular front depends on two things:
(36) _______________________________________
(37) _______________________________________.
A (38) ______________________________________ is the boundary between an
advancing cold air mass and a warmer air mass. Since cold air is denser than warm air, the cold
air slides underneath the warm air, forcing it upward. Cold fronts can create thunderstorms, or
cause no greater change than a shift in wind direction. In the summer, some cold fronts cause a
decrease in humidity, while in the winter a cold front can cause
(39) _________________________________
(40) _________________________________.
If warm air moves cold air, the boundary between the air masses is known as a
(41) _____________________________________. The advancing warm air rises above the
denser cold air, which moves away slowly. The first signs of a warm front are high cirrus clouds,
which are followed by cirrostratus clouds and lower and thicker stratiform clouds. Such clouds
form in the warm, stable air sliding up the front surface. These clouds may stretch 1500
kilometers ahead of the place where the warm front touches the ground; this cirrus clouds may
warn of approaching (42) ___________________________________.
Cold fronts usually move (43) _______________________ as fast as warm fronts. If a
cold front “catches up” to a warm front, the result is an
(44) ______________________________________________. The warm air that is caught
between the two colder air masses is forced to rise. Once this warm air rises, it cools, often
resulting in:
(45) ______________________________
and
(46) ______________________________.
If a front is not moving forward, it is called a (47) ____________________________________.
The warmer air rises over the denser, colder air, and clouds and precipitation may form.