Name ___________________________
Period _____________
Air Masses and Weather Fronts
Air Masses
A. An air mass is a large section of the air (lower _Troposphere___ ) in which
the temperature and humidity are about the ____same______ throughout.
B. Characteristics of air masses:
1. The two main characteristics that define an air mass are
___temperature___ and ___humidity____.
2. These two characteristics are determined by the surface over which
they _____formed_______ (source region).
3. On a weather map, air masses are identified and described according
to their source regions (case specific):
(temperature characteristic)
a. Arctic -Very high latitude (Alaska) cold air - _____A_____
b. Polar - High latitude (Canada) cold air
- _____P______
c. Tropical - Low latitude (Mexico) hot air
-_____T______
(humidity characteristic)
d. Maritime - Over water (oceans), wet air
-_____m______
e. Continental - Over land, dry air
-______c_____
4. The abbreviations for the four main air masses that affect the
continental United States are ____cP____, ____mT____, ___cT___,
and ____mP____.
C. Place the proper abbreviation for each air mass in the circles on the map
D. Weather in an air mass:
1. Weather in a cP air mass is generally ___cold/dry_________.
2. Weather in an mT air mass is generally _____warm/moist_______.
3. Air masses may undergo changes. For example, air masses moving
south will tend to become ___warmer_____, while those that move
north will become ____colder______.
E. Air mass practice:
1. The symbol for a cold and dry air mass is ____cP, cA_____.
2. The symbol for a cold and wet air mass is ____mP________.
3. The symbol for a warm and wet air mass is ___mT________.
4. The symbol for a warm and dry air mass is ____cT_______.
5. The “c” in cP indicates that the air mass originated over a
_____land_______ region and is relatively ___dry______.
6. The “m” in mP indicates that the air mass originated over
____water______ and is relatively ___moist_____.
7. The “P” in mP indicates that the air mass originated in the
____polar_____ regions or __high____ latitudes and is relatively
____cold_______.
8. The “T” in mT indicates that the air mass originated in the
__tropical______ regions or ___low___ latitudes and is relatively
____warm______.
High & Low Pressure Systems
A. High Pressure System (H):
1. At the ___center____ of all air masses, the air is descending (falling)
to the surface causing high pressure.
2. Once the air reaches the surface the air _____diverges_____, or
spreads out, away from the high pressure center.
Notice the air falling at
the center causing
high pressure.
3. Due to the Coriolis Effect, the diverging surface winds turn to the
____right (clockwise)______ in the northern hemisphere.
Notice the outward spiraling
surface winds turning right.
4. This clockwise, spiraling outward wind is why high pressure systems
are called ______anti-cyclones_______
B. Low Pressure System (L):
1. In a low pressure system, air ___rises_____, which causes low pressure
and causes winds to ____converge_____ towards the low pressure center.
Notice the air rising at
the center causing low
pressure.
2. This counterclockwise, convergent, spiraling inward (with a turn to the
right) surface wind is why low pressure systems are called
_____cyclones________.
Notice the right turn to the
spiraling inward surface winds.
Weather Fronts
A. A weather front is defined as the boundary between two different
_____air masses__. The importance of fronts is that their passage always
indicates a change in weather and is usually accompanied by
__precipication___.
B. Warm Front:
1. A warm front forms when a warm air mass _collides_ with a cold
air mass.
2. Since warm air is ___less__ dense than cold air, the warm air
slowly glides up and over the back of the cold air.
3. This gliding effect causes the warm front to have a __gentle____
slope.
Cloud Type
Warm Air
Ns – Nimbostratus
As – Altostratus
Cs – Cirrostratus
Ci – Cirrus
4. Point C on the diagram shows the position of the warm front at the
surface. A series of __stratus___-type clouds precede the passage
of a warm front that extend ___600-900____ miles ahead.
5. Steady precipitation is experienced for several hundred miles
___ahead____ of the front.
C. Cold Front:
1. A cold front forms when a cold air mass ___collides____ with a
warm air mass (just the opposite of a warm front).
2. Since cold air is _more__ dense than warm air, the cold air
“bulldozes” underneath the warm air.
3. This bulldozing effect causes the cold front to have a __steep___
slope.
Cloud Type
Cu – Cumulus
Cb – Cumulonimbus
4. Point D on the diagram shows the position of the cold front at the
surface. Its passage is generally accompanied by _cumulus_-type
clouds ___along_____ the front.
5. A strong line of thunderstorms is frequently found just ahead of the
front, which is called a __squall____ line.
D. Occluded front
1. An occluded front occurs when a cold front __overtakes___ a warm
front. This occurs because cold fronts are generally _faster___
than warm fronts.
2. The cold and the cool air masses force the warm air mass __up_.
3. The weather along an occluded front __combines__ the
characteristics of both types of fronts, which usually results in an
__increased___ amount of cloudiness and precipitation.
Warm Air
Mass
Cold Air Mass
Cool Air Mass
E. Stationary Front
1. A stationary front is produced when two different air masses are not
____moving____.
2. The weather of these fronts most closely resembles __warm__
front weather.
F. The passage of a front is ___always__ accompanied by a change in
__wind__ direction and speed.
G. On a weather map, there are symbols to represent the different fronts.
These symbols can be found in your reference tables on page __13_.
H. In the following boxes, draw the front symbols for each front. Also, add
the abbreviations for the appropriate air masses.
Cold Front
Warm Front
Occluded Front
Stationary Front