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
Meeting of cold air and warm air
Colliding air masses
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.
Chapter 24-3 What causes severe storms?
Objective- Identify three types of severe storms.
Thunderstorm- storm with thunder, lightning, and often heavy rain and
* 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
• Lightning discharges an excess of positive and negative charge
within clouds, between clouds, or between clouds and the ground.
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.
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.
Tornado- small very violent funnel-shaped cloud that spins.
* Low pressure storm that forms over a small area with very violent
Waterspout- tornado that forms over water.
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
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.
The winds of a hurricane grow stronger and more destructive the closer
to the eye.