1. Chapter 24-1 Air Masses
Air Mass- large volume of air with about the same temperature and amount of moisture.
* Air masses take on characteristics of their source region.
Air masses that form over land are dry.
Air masses that form over water are moist
Types of Air Masses
cP-continental polar: dry and cold
mP- maritime polar: moist and cold
cT- continental tropical: dry and warm
mT- maritime tropical: moist and warm

2. Meeting of cold air and warm air
Colliding air masses

3. Chapter 24-2 Fronts
Front- boundary between air masses of different densities.
*fronts can be hundreds of kilometers long
* fronts bring changes in weather.
* cold air is denser than warm air
Types of Fronts:
Cold front- forward edge of a cold air mass, formed when a cold air mass pushes under a warm air mass.
* have steep leading edges and dense air.
* heavy rainfall of short duration
* cumulonimbus, cumulus clouds
Warm front- forward edge of a warm air mass, formed when a warm air mass pushes over a cold air mass.
* has a gentle leading edge and less dense air.
* light to moderate rainfall and stratus, nimbostratus clouds.
Occluded front- Occurs when a cold front over takes a warm front.
* Violent weather, cumulonimbus clouds, lightning, thunder
Stationary Front- When two air masses meet and fail to move for an extended period of time.
* light to moderate rainfall of long duration.

4. Fronts
Warm/Cold Front

5. Fronts
Occluded

6. Fronts
Occluded

7. Front
Warm Front

8. Chapter 24-3 What causes severe storms?
Objective- Identify three types of severe storms.
Thunderstorm- storm with thunder, lightning, and often heavy rain and strong winds.
* Usually forms in summer when air becomes unstable and large cumulonimbus clouds develop vertically.
Lightning- electrical discharge created in clouds from a build-up of charges.
Lightning discharges an excess of positive and negative charge within clouds, between clouds, or between clouds and the ground.

9. Lightning
Lightning kills or injures 1,000’s of people each year worldwide.
*Only one out of 500,000 people are killed by lightning and only about one in 125,000 people are injured.

10. Chapter 24-3 Severe Storms
Thunder- sound wave produced by superheated air.
*When the potential difference between the regions gets too great, lightning flashes, heating the discharge channel to sun-surface temperatures. The air expands explosively, forms a shock wave, and thunder cracks — nature’s sonic boom.

11. Chapter24-3 Tornadoes
Tornado- small very violent funnel-shaped cloud that spins.
* Low pressure storm that forms over a small area with very violent winds.
Waterspout- tornado that forms over water.

12. Tornado- What causes a tornado?
Low pressure develops from colliding air masses; usually mT and cP, As the air mass rises, it is affected by shear winds traveling in the upper troposphere.

13. Chapter 24-3 Hurricanes
Hurricane- tropical low pressure storm with very strong winds.
*Hurricanes form over warm tropical waters, from low pressure created by warm/moist rising air. As the air rises, it spins inwards towards the center at speeds of 300 km/hr.

14. Hurricanes
The winds of a hurricane grow stronger and more destructive the closer to the eye.