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.

Fronts Warm/Cold Front

Fronts Occluded

Fronts Occluded

Front Warm Front

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.

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.

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.

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.

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.

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.

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