1. 12-7
What are air masses?

2. 12-7 Air Masses
Air mass- large volume of air with same temp. and moisture.
Air mass is affected by the region it covers- land, ocean, hot, or cold.
Masses can be dry, moist, warm, or cold.

3. 12-7 Polar Air Masses
Polar air masses- cold air masses that form over cold regions.
Continental polar air mass- a dry polar air mass that forms over land and forms over Canada and moves into the US.

4. 12-7 Polar Air Masses
Maritime polar air masses- moist, cold air masses that form over oceans and move into US via north Pacific and Atlantic Oceans.

5. 12-7 Tropical Air Masses
Tropical air masses- warm air masses that form over the equator.
Maritime tropical air masses- moist, warm air masses that form over water. US is affected by those that form over Caribbean and Gulf of Mexico and the oceans.

6. 12-7 Tropical Air Masses
Continental tropical air masses- dry, warm masses that form over land, usually coming from Mexico to the US.

7. Jet Streams Jet streams are currents of fast moving air.
They travel more than 300 km per hr. in a west to east direction.
They form due to temp. and air pressure differences.

8. 12-7 Lesson Summary
Air mass- large area of air with same temp. and moisture content.
Air mass is affected by the region it covers.

9. 12-7 Lesson Summary
Polar air masses- cold regions; may be maritime polar or continental polar.
Tropical air masses- form near equator; may be continental or maritime air masses.

10. 12-7 Class Work
Complete Checking Concepts and Thinking Critically.

11. 12-8
What is a front?

12. 12-8 Boundaries in Air
Front- the front surface/edge between different air masses.
Air masses move from W to E in the US.
As air masses move, they do not meet, but instead form fronts between them that bring changes in the weather.

13. 12-8 Cold Front Cold front- forward edge of a cold air mass.
Cold front forms when a cold air mass pushes under a warm air mass.
Cold fronts usually bring t-storms, gusty winds, cloudy skies, and cold air behind them.

14. 12-8 Warm Fronts Warm front- the forward edge of a warm air mass.
A warm front forms when a warm air mass pushes over a cooler air mass.

15. Warm Front, cont.
Cirrus clouds then stratus clouds form as warm front moves, and long, steady precipitation usually follows.
After front pushes through,slow clearing and warmer temperatures remain.

16. Stationary Front
Stationary front- when cold or warm masses stay in place a long time and do not move.
The weather will remain whatever is around that front until the front changes.

17. Occluded Fronts A warm mass “wedges” between two cold air masses.
The cold masses push the warm mass upwards and then push each other, resulting in cloudy, rainy, or snowy weather/violent forms.

18. 12-8 Summary Front- surface between two different air masses.
Cold front- forward edge of a cold air mass.
Warm front- forward edge of a warm air mass.

19. 12-8 Summary
Stationary front- forms when two air masses meet and stay in one place a while.
Movements of fronts causes changes in weather.

20. 12-8 Class Work
Complete Checking Concepts and Thinking Critically.