1. Air Masses What are major air masses?
What are the main types of fronts?
What is a hurricane?

2. What are the major air masses?
An air mass is a huge body of air in the lower atmosphere that has similar temperature, humidity and air pressure
Four major types of air masses influence the weather in North America:
maritime tropical,
continental tropical
Maritime polar
Continental polar

3. How do Air masses move?
When an air mass moves into an area and interacts with other air masses, it causes the weather to change
Prevailing westerlies are the major wind belts across the United States, generally push are masses from west to east
Jet streams are bands of high speed winds about 10 kilometers above Earth’s surface
Fronts are the boundaries where air masses meet. Storms and changeable weather often develop along fronts

4. Cold Fronts
Remember, cold air is dense and sinks, warm air is less dense and tends to rise
When colder, dense air runs into warm, less dense air, the warm air is pushed up.
Warm air can hold more water vapor, so as this air is forced upward, the water condenses
Clouds form and heavy rain or snow may happen
Cold fronts tend to arrive quickly and bring thunderstorms
After a cold front passes, there will be clear skies, and cooler temperatures

5. Warm Fronts Clouds and precipitation often accompany warm fronts
Because cold air is denser, the warm air moves over the colder air
If the warm air is humid, you will get rain and clouds for several days
After a warm front passes, the weather tends to be warmer and humid

6. Stationary fronts
Sometimes cold and warm air masses meet, but neither can move the other
Where the warm and cool air meet, water capor in the warm air condenses
If a stationary front stalls, it may bring many days of clouds and precipitation

7. Occluded Fronts
The most complex weather situation occurs at an occluded front
A warm air mass is caught between two cooler air masses
The denser cool air moves under the warmer air and pushes it upward
The warm air mass is cut off from the ground and the water vapor in it condenses
Rain or snow may fall

8. Hurricanes
A Hurricane is a tropical cyclone with winds of 119 km/h (74 mph) or higher
A hurricane begins over warm ocean water as a low pressure area, or tropical disturbance
The role of the oceans in the formation of hurricanes is to store the heat and moisture that the storm needs to develop
Hurricane winds are strongest around its center or eye wall