What happens when air masses meet?

What is an air mass? Large volume of air with uniform temperature and humidity readings Gets its characteristics from where it forms Continental: forms over land (dry) Maritime: forms over water (moist) Tropical: forms near equator (warm) Polar: forms nearer poles (cold)

Continental Air Masses Polar (cP) Tropical (cT)

Maritime Air Masses Tropical (mT) Polar (mP)

What happens when different air masses meet? Boundary between two different air masses is a: FRONT

Types of Fronts Cold Front Warm Front Stationary Front Occluded Front

What happens in a cold front?

Cold air moves into warmer air

Cold Front Cold air moves in, replaces warm air Cold air is more dense than warm air Cold air pushes warm air up Tall clouds form (cumulus and cumulonimbus)

Clouds are right along the front Precipitation is brief, but heavy (thunderstorms) Band of precipitation 75 miles around front (about 50 miles ahead and 25 miles behind) (about 50 miles ahead and 25 miles behind)

75 miles

Air pressure is lowest at front After front passes: colder air mass temperature drops temperature drops skies clear skies clear pressure increases pressure increases Cold fronts move faster than warm fronts (about 30 mph)

Weather map symbol

Warm air moving into cold Predictions?

Warm air moving in

What happens with a warm front? Warm air mass advances and replaces cold air mass Warm air is less dense than cold Warm air rides above the colder air

Warm Front

Clouds start to form 1000 miles ahead of the front Cirrus clouds develop, followed by lower level stratus clouds Belt of precipitation is about 300 miles wide (starting miles ahead of the front)

1000 miles

Rain (precipitation) is gentle, but may last for a long period (several hours or days) Weather changes slowly (front moves about 20 mph) Warmer air finally replaces the colder air

As the front passes: Temperature increases Skies clear Pressure increases

Weather map symbol

Fronts – boundary that separates 2 air masses with different temperatures

Clouds: altostratus Warm front

Cold Front

HINT: sudden burst of intense rain over a small area Cold Front

HINT: this is a squall line Cold front

Stratus clouds: warm front

Clouds on Monday Clouds on Tuesday Warm front

Another squall line: COLD FRONT Robin Brueckner 2004

HINT: low gray clouds, long period of light snow WARM FRONT!!!!!!!!

Cold Front

Cold front Sharp break between air masses

Stationary Front

A stationary front occurs when the air masses on either side of the front are not moving toward each other.

Stationary Front Neither air mass pushes into the other Generally causes unsettled conditions –Rain, clouds, etc… Flooding may occur if front does not pass

OCCLUDED FRONT Warm air mass gets caught between 2 colder air masses and is forced aloft

Formation of an Occluded Front

Occluded Front A cold air mass catches up to another cold air mass Warm air is ‘squeezed’ out in the middle Causes precipitation

Important Vocabulary Air mass – (cT, cP, mT, mP, cA) Front Warm front Cold front Occluded front Stationary front

Winds spiral clockwise out of the High and counterclockwise into the Low Fronts are low pressure – lousy weather After the front passes – happy weather

Weather in a High Clockwise Rotation Bright, Clear Happy Weather

Hurricanes – counterclockwise low pressure systems (lousy weather)