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Air Masses and Severe Weather. Integrated Science. Air Mass. Huge volumes of air that can cover entire continents or oceans Several types that each have specific characteristics see text p. 689. Atmospheric Lifting. Clouds are indicators of weather

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Air Masses and Severe Weather

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Air masses and severe weather

Air Masses and Severe Weather

Integrated Science

Air mass

Air Mass

  • Huge volumes of air that can cover entire continents or oceans

  • Several types that each have specific characteristics

  • see text p. 689

Atmospheric lifting

Atmospheric Lifting

  • Clouds are indicators of weather

  • For clouds to form, air must be lifted

  • Three types of lifting cause clouds.

Lifting type 1

Lifting Type #1

  • Convectional Lifting

  • Earth’s surface is heated by the sun, which heats the air mass above it. The heated air will then rise.

Convectional lifting

Convectional Lifting

Convectional lifting1

Convectional Lifting

  • If cooling occurs near the air mass’ saturation temperature, often cumulus clouds may form

Convectional lifting2

Convectional Lifting

  • Often happens in the mid-west during summer

Atmospheric lifting type 2

Atmospheric Lifting Type #2

  • Orographic Lifting

  • An air mass is pushed upward over an obstacle, such as a mountain range.

Atmospheric lifting type 2 orographic

Atmospheric Lifting Type #2Orographic

  • As the air mass is pushed over the obstacle, the air mass will lose moisture in the form of clouds, rain, or snow

Atmospheric lifting type 21

Atmospheric Lifting Type #2

Atmospheric lifting type 22

Atmospheric Lifting Type #2

Atmospheric lifting type 23

Atmospheric Lifting Type #2

  • The clouds dump their load of rain on the windward slope

  • The down slope (leeward) air will be dry = rain shadow

Rain shadow orographic lifting

Rain shadow- orographic lifting

Rain shadow

Rain shadow

  • Western Kansas is so dry only certain short grasses can grow; not enough rain for trees

Rain shadow big hatchet mt new mexico notice how dry the land is

Rain Shadow; Big Hatchet Mt, New Mexico. Notice how dry the land is

Orographic lifting chinook winds

Orographic Lifting – Chinook Winds

  • At the high elevations of the top of a mountain, the air pressure is low.

  • As the air descends the mountain is under more pressure.

  • The increased air pressure heats the air causing warm winds called Chinook Winds

  • Temperatures can rise 20-300 as air moves down the mountain

Chinook winds

Chinook Winds

Atmospheric lifting type 3

Atmospheric Lifting Type #3

  • Frontal Lifting

  • This occurs at the mesh point between two different temperature air masses.

  • One air mass (warm) is pushed upward by the other (cold).

  • This can be associated with thunderstorms.

Frontal lifting

Frontal Lifting

  • Three types of frontal lifting

  • A) warm front

  • B) cold front

  • C) Stationary front

Frontal lifting1

Frontal Lifting

  • Cold Front: When a cold air mass moves into a warm air mass.

  • Cold, denser air forces the warm air up where it cools and condenses, forming clouds

Cold front

Cold Front:

  • Warm air is abruptly pushed upward, cooling, condensing moisture into cumulus or cumulonimbus clouds

Cold front1

Cold Front

  • Notice how steep the angle is between the two air masses

  • Typically brings sudden, heavy rains and storms

Cumulonimbus lake superior

Cumulonimbus: Lake Superior

Warm front

Warm Front

  • WARM FRONT: when a warm air mass moves into a colder,denser air mass.

  • Warm air rides up and over the colder air

Warm front1

Warm front

Warm front2

Warm Front

  • Notice the angle of slope between the two air masses.

Warm front3

Warm Front

  • From the ground, one would observe the following cloud sequence

  • A) cirrus

  • B) cirrostratus

  • C) altostratus

  • D) stratus

  • E) nimbostratus

Warm front4

Warm Front

  • The weather during a WARM FRONT starts with cirrus clouds about 24-48 hours before the rain begins

  • Cirrus clouds are “at the front of the front”

Warm front5

Warm Front

  • As more warm air is pushed upward, more moisture condenses forming cirrostratus clouds

Cirrostratus on lake superior

Cirrostratus on Lake Superior

Warm front6

Warm Front

  • As warm more warm air is pushed up, heavier clouds form mid-way up over the cold air

  • Altostratus and stratus

Altostratus clouds lake superior

Altostratus clouds: Lake Superior

Warm front7

Warm Front

  • The final cloud type in a warm front is the nimbostratus

  • “nimbo” = “rain”

Warm front8

Warm Front

  • Warm front: rain or snow is steady over several hours or days

Quiz yourself t or f

Quiz Yourself!!! T or F

Quiz t or f

QUIZ: T or F

  • For clouds to form, air must be lifted

  • There are FOUR different types of lifting

  • Orographic lifting refers to air movingup and over a mountain

Quiz t or f1

QUIZ: T or F

  • Convectional lifting is the circulation of warm air rising, cold air sinking

  • A rain shadow is caused by WET air descending down the leeward side of a mountain

  • A WARM FRONT means warm air is riding up over cold air

  • A WARM FRONT produces sudden, severe rain and storms

Severe weather

Severe Weather



  • Cold Fronts

  • Begins with humid air rising, cooling, and condensing into a single cumulus cloud.

  • Cloud builds as they are “fueled” by warm, moist air from below.



  • The droplets of water grow larger until they are so big that they fall as rain.

Cumulonimbus clouds l superior

Cumulonimbus clouds: L Superior

Thunderstorms con t

Thunderstorms (con’t)

  • Lightning may be associated with T.storms

  • Hits Earth 100 times per second

  • Over 200 people in the US die each year from lightning.



  • Lightning is the cause of thunder

  • returns nitrogen to the soil

  • may cause fires

  • May have helped start pre-biotic formation of amino acids(?)

Lightning formation

Lightning Formation

  • During thunderstorms strong updrafts cause molecules to bump together and their charges to separate

  • Negative charges concentrate at the base of the clouds

Lightning formation1

Lightning Formation

  • The ground has lost electrons, giving it a positive (+) charge

  • Opposites attract: The (-) from the cloud base is “pulled” to the (+)

  • First downward movement of (-) is called a leader

Lightning formation2

Lightning Formation

  • When the (-) and (+) touch, they create a conductive path to the ground.

  • The other (-) rush down this path = lightning

Lightning on l superior

Lightning on L.Superior

Lightning on l michigan

Lightning on L.Michigan

Lightning strike

Lightning strike

Quiz yourself true or false

Quiz Yourself!! TRUE or FALSE

True or false

TRUE or FALSE?????

  • Cumulonimbus clouds can become thunderstorms

  • Stratus clouds produce sudden, severe thunderstorms and lightning

  • Lightning forms because of unequal charges



  • A funnel shaped cloud that extends downward from a cumulonimbus cloud.

  • Called a tornado only once it hits the ground.

  • Winds inside travel at up to 800km per hour in counterclockwise direction.



  • Caused by a warm, vertical wind interacting with an existing storm and causing the storm to turn inward and spiral.

  • Wind speeds of up to 300km per hour.

  • Hurricanes grow as more moist air rises into it.

  • Severe winds rotate around a calm, low pressure zone in the middle, which is the eye of the storm.

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