1. Air masses and fronts
1. An air mass is a wide-spread section of the troposphere with uniform temperature and humidity (moisture)
2. The source region is the geographic location the air mass developed over.
If air settles over one location for a long time, it develops the characteristic temperature and moisture of the area.
Uwsp.edu

2. Oceans (maritime) give Air a lot of water vapor
Because temperature changes so much with latitude, tropical areas are warm and polar are cold.
Oceans (maritime) give Air a lot of water vapor
On land, (continental) there is little water and the air is dry.
blueollie.wordpress.com

3. Page 13 ESRT uses symbols for the air masses
Dry air is small ‘c’ for continental
Moist air is small ‘m’ for maritime
Cold air is ‘P’ for Polar and REALLY cold air is ‘A’ for arctic.
Warm air is ‘T’ for tropical
Geography.hunter.cuny.edu

4. And to practice:
2. The characteristics of the air mass is due to the source region, or area where it formed. For each of the following locations create our air mass (and weather), identify the characteristics of the air, using the terms continental, maritime, tropical, arctic and polar.
Gulf of Mexico:
Central Mexico:
Great Plains (winter):
Central Canada:
Northern Atlantic:
1. Bringing those two characteristics together, the air masses may be described. For the following, identify the characteristics:
cT:
mT:
cP:
mP:
cA:
Air masses and polar fronts:
for air masses

5. Fronts: the boundary between two air masses
A boundary describes where two different things meet.
Between countries
Between lawns
Between air and land.
A frontal boundary is where two different air masses meet. Energy is exchanged.
Fronts bring a change in weather.
One type of air mass pushes in and replaces another one.
“Bad weather” (storms and precipitation) occurs at fronts.

6. How severe the storm is depends on:
how quick the change is and the differences between the 2 air masses:
a REALLY warm, moist air mass meeting a REALLY cold, dry air mass will produce dramatic weather/storm. This is what caused last week’s tornadoes!!!
How much moisture is in the warm air mass.
weather.thefuntimesguide.com

7. The winds in a storm, tend to make a counterclockwise rotation.
The type of front created depends on the direction the air masses move and the way the air masses meet.
Prevailing Winds: In the U.S., our weather systems tends to move from west to east.
The winds in a storm, tend to make a counterclockwise rotation.
scoutweatherbadge.wordpress.com

8. At Fronts:
Clouds form: because warm, moist air is pushed up at the boundary by the heavier, colder air mass.
Clouds form as rising air cools to the dew point temperature and water vapor condenses around condensation nuclei, such as soot or ash.
Precipitation happens at the front
explore.ecb.org

9. Cold Fronts
Side view:
physicalgeography.net
geography.hunter.cuny.edu

10. Cold front overview
Cold front, heavy, dry, cold air replaces light, warm air .
dramatic cumulonimbus clouds, lots of wind, and brief and intense precipitation.

11. Warm front: side view nauticed.org

12. Precipitation happens ahead of the front.
The wedge-shape front is caused by the warm air slowly pushing up along the boundary.
Precipitation happens ahead of the front.

13. Warm front: map overview
Warm front, in which warmer air replaces colder air. The effect is cirrus and stratus clouds, steady precipitation that may last for a day or two.
Usually, the warm air has more moisture.
The warm air is pushed up at the frontal boundary, causing clouds to form.
gcel.com.mx

14. Occluded front: side view
physicalgeography.net
aos.wisc.edu

15. Occluded front, in which a cold air mass wraps around a warm air mass, actually lifting the air off the ground.
This causes a REALLY dramatic change in weather, intense winds and violent precipitation. (Nor-easters, some tornadoes and t-storms)
allposters.com

16. Stationary front lewistonpublicschools.org

17. Stationary fronts may last for days because the 2 air masses just don’t really move. Usually, the characteristics are similar to the warm front, just prolonged.
Again, it is the warmer air that is pushed up because it is less dense.
Why clouds???
Rising air expands and COOLS.
Water vapor CONDENSES.