17.1 – Air Masses and 17.1 – Air Masses and FrontsFronts

► An air mass is a huge An air mass is a huge body of air that has body of air that has similar temperature, similar temperature, humidity, and air humidity, and air pressure throughout.pressure throughout.

Types of Air MassesTypes of Air Masses

► Scientists classify air Scientists classify air masses according to masses according to temperature and humidity.temperature and humidity.

► There are four major types There are four major types of air masses that influence of air masses that influence weather in N. America.weather in N. America.

1.1. Maritime TropicalMaritime Tropical – – ► Warm, humid air Warm, humid air

masses that form over masses that form over the the oceansoceans and Gulf of and Gulf of MexicoMexico

► They travel up from They travel up from the south bringing the south bringing warm, humid air. warm, humid air.

►Bring showers and Bring showers and thunderstorms in the thunderstorms in the summer.summer.

► Bring snow in the Bring snow in the winter.winter.

2. 2. Maritime PolarMaritime Polar

► Cool, humid air masses Cool, humid air masses that form over the North that form over the North Pacific and Atlantic Pacific and Atlantic OceansOceans..

► They affect the West They affect the West Coast more than the East Coast more than the East Coast.Coast.

► They bring rain, and They bring rain, and cool temps to the west cool temps to the west coast.coast.

3. 3. Continental TropicalContinental Tropical

► Hot, dry air masses that Hot, dry air masses that form only in summer form only in summer over areas in the SW over areas in the SW U.S. and N. Mexico.U.S. and N. Mexico.

► They move NE, bringing They move NE, bringing hot dry weather.hot dry weather.

4. 4. Continental PolarContinental Polar

► Large air masses that Large air masses that form over N. Canada form over N. Canada and Alaska.and Alaska.

► Bring cool, dry air to Bring cool, dry air to much of North America.much of North America.

FRONTSFRONTS► As huge masses of air As huge masses of air move across land and move across land and water, they bump into water, they bump into each other.each other.

►When 2 masses with When 2 masses with different temps and density different temps and density collide, they do not mix.collide, they do not mix.

► The area where the air The area where the air masses meet and do not masses meet and do not mix becomes a “mix becomes a “frontfront””

► A front forms because A front forms because one air mass is less one air mass is less dense than the other air dense than the other air mass.mass.

► There are 4 types of There are 4 types of fronts: cold fronts, warm fronts: cold fronts, warm fronts, stationary fronts, fronts, stationary fronts, and occluded fronts.and occluded fronts.

Cold Fronts

► Cold fronts form when Cold fronts form when a rapidly moving cold air a rapidly moving cold air mass runs into a slowly mass runs into a slowly moving warm air mass.moving warm air mass.

► Often results in the Often results in the formation of clouds, formation of clouds, rain, and/or snow.rain, and/or snow.

► Also, thunderstorms. Also, thunderstorms.

Warm Fronts► Forms when a rapidly Forms when a rapidly moving warm air mass moving warm air mass collides with a cold air collides with a cold air mass.mass.

► Can cause rain or fog. Can cause rain or fog. ► Slower moving than Slower moving than cold front.cold front.

Stationary Fronts► Forms when a warm air Forms when a warm air mass and a cold air mass and a cold air mass meet and no mass meet and no movement occurs.movement occurs.

► Neither air mass has Neither air mass has enough force to move enough force to move the other.the other.

Occluded Front► Forms when a warm air Forms when a warm air mass is caught between mass is caught between two cooler air masses.two cooler air masses.

► The warm air mass The warm air mass gets lifted and cut off gets lifted and cut off from the ground by the from the ground by the two cooler air masses.two cooler air masses.

17.2 - Storms17.2 - Storms

► A swirling center of low air A swirling center of low air pressure is called a pressure is called a cyclonecyclone..► As warm air at the center of As warm air at the center of the cyclone rises, cooler air the cyclone rises, cooler air blows toward this from areas blows toward this from areas with higher pressure.with higher pressure.

► The winds swirl in a The winds swirl in a counter-clockwise fashion counter-clockwise fashion b/c of the Coriolis Effect.b/c of the Coriolis Effect.

► Cyclones and low pressure Cyclones and low pressure areas are associated with areas are associated with storms and precipitation.storms and precipitation.

► Anticyclones are the Anticyclones are the opposite of cyclones.opposite of cyclones.

► They are areas of high They are areas of high pressure that are pressure that are associated with dry and associated with dry and clear weather.clear weather.

► Air blows from high Air blows from high pressure areas to low pressure areas to low pressure areas.pressure areas.

Kinds of StormsKinds of Storms► A storm is a violent A storm is a violent disturbance in the disturbance in the atmosphere.atmosphere.

► Storms involve sudden Storms involve sudden changes in air pressure, changes in air pressure, which cause rapid air which cause rapid air movements.movements.

HurricanesHurricanes► A hurricane is a tropical A hurricane is a tropical storm that has winds of storm that has winds of 74mph or greater.74mph or greater.

► They begin over warm They begin over warm water as a low pressure water as a low pressure area.area.

► The center of a hurricane The center of a hurricane is a ring of clouds is a ring of clouds surrounding a quiet “eye”surrounding a quiet “eye”

► When the eye arrives, the When the eye arrives, the winds grow calm and the winds grow calm and the sky may clear.sky may clear.

► Hurricanes can last for Hurricanes can last for over a week. over a week.

► They get their energy from They get their energy from the warm, humid air at the the warm, humid air at the ocean’s surface.ocean’s surface.

► When they get over land, When they get over land, they begin to lose energy.they begin to lose energy.

TornadoesTornadoes► Tornadoes form in low, Tornadoes form in low, heavy cumulonimbus heavy cumulonimbus clouds.clouds.

► They form when cold, dry They form when cold, dry air mass from Canada air mass from Canada collides with a warm, humid collides with a warm, humid air mass from the Gulf of air mass from the Gulf of Mexico.Mexico.

► During a tornado, the During a tornado, the safest place to be is in the safest place to be is in the basement of a well-built basement of a well-built building.building.