1. Air Masses and Weather Fronts
Lesson 5

2. What is an air mass?

3. United States’ Air Masses (Page 49)

4. What happens when air masses meet?
The boundary between air masses is called a
There are 4 types and they can be found on page:
63 in your Catastrophic Events Book (Only 3)
222 in your ScienceSaurus (All 4 with symbols)
Animations can be found on the following link:

5. What happens when air masses rise or sink?
When a “warmer” air mass is rising you have low atmospheric (barometric) pressure.
This is represented by a red L on a weather map.
When a “cooler” air mass is sinking you have a higher atmospheric (barometric) pressure.
This is represented by a blue H on a weather map.

7. What makes the wind blow?
When a cooler sinking air mass rushes in to take the place of a warmer rising air mass we get wind.
Wind almost always goes from a higher pressure H area to a lower pressure L area.