1. Weather Patterns Air Masses and Fronts
Section 17.1

2. Air Masses
Arctic
Maritime
polar
Continental
polar OK
Maritime
tropical
Continental
tropical
Huge bodies of air that have similar temperature, humidity, and air pressure

3. Fronts
When an air mass moves into an area and interacts with other masses, it causes the weather to change.
The boundary where air masses meet becomes a front

4. Cold Front Since cold air masses move fast they can cause abrupt
Fast moving cold
dense air pushes
slow moving
warm air up
Warm air cools
and precipitates
Since cold air masses move fast they can cause abrupt
weather changes (thunder storms)
After a cold front passes, colder, drier air moves in
bringing clear skies

6. Warm Front Less dense warm air moves over dense cold air
Fast moving
warm air
overtakes
slow moving
cold air
Less dense warm air moves over dense cold air
Can produce rain or snow
Area likely to become warm and humid

7. Warm Front

8. Stationary Fronts Standoff between two air masses
Cold air and warm air meet but neither can move the other.
Produces rain, snow or fog
Can last for several days
Standoff between two air masses

9. Stationary Fronts
Standoff between two air masses

10. Occluded Front A warm air mass is caught between two cold air masses
The denser air mass pushes the warm air mass up
The two cold air masses may mix underneath the warm one
The warm air mass is cut off (occluded) from the ground
The warm air cools, condenses and may precipitate

11. Cyclones & Anticyclones
Fronts become distorted because of things like mountains or jet streams (bending)
Bending can cause swirls which can create low pressure centers

12. Cyclones Swirling low pressure system
Air pressure decreases as warm air rises
Cooler air blows inward toward the low pressure area
Coriolis effect causes the wind to spin counterclockwise in northern hemisphere
Associated with clouds, wind, and precipitation

13. Anticyclones High pressure systems
Air swirls outward in clockwise direction in northern hemisphere
Cool air moves downward and heats up lowering relative humidity
Associated with dry, clear weather