5.2 Weather Patterns

Pages 173-177

Pressure Systems

•Air pressure is the force of air on the surface.

•Air Pressure is greatest near Earth’s surface and decreases as altitude increases.

•High air pressure always moves toward areas of Low Pressure

•Hot Air Rises Cold Air Sinks

High Pressure •cold air from above

sinks and creates a high pressure system on the ground

•low pressure is on either side of the HP

•HP moves toward LP and creates wind circulating clockwise

•Brings sunny fair weather with light winds

•Represented on a weather map as a blue

H

Low Pressure •warm air on the ground

forms a low pressure system with high pressure on either side

•HP moves toward LP creating counter-clockwise winds

•the warm air rises, condenses and forms clouds

•Brings stormy weather with strong winds

•Represented on a weather map as a red

L

Air Masses •large bodies of air that have a similar humidity (moisture), temperature and pressure (high)

•the air must remain above a high pressure system, known as a “source region” for at least a couple of days

•Source region is the location the air mass forms• Ex. if an air mass forms over Canada, Canada is considered the source region

•As the winds begin to move the air mass from it’s source region, it begins to bring the moisture and temperature to a new location

Naming Air Masses •Air masses are

given a two word name that describes it’s moisture and temperature

• Moisture/Humidity (1st word)

continental (c) forms over land – dry

maritime (m) forms over water –

wet/humid/moist

• Temperature (2nd word)

Tropical (T) forms in warmer regions,

hot

Polar – (P) forms in cold regions – cold

Arctic – (A) forms in arctic regions-

bitterly cold and dry

Weather Fronts

•A boundary between two different air masses, resulting in a change of weather

•Temperature, humidity, clouds, precipitation, and winds

Cold Front1. cold air mass approaches a warm air mass

2. dense cold air moves under the warm lighter air and forces the warm air to rise

3.tall vertical clouds form which result in stormy weather and colder temperatures

•A cold front is represented as a blue line with the triangles pointing toward the direction on movement. 

Warm Front1. a warm air mass approaches a cold air mass

2. less dense warm cannot move under the cold air so it slides over the top

3. produces clouds, precipitation, and warmer temperatures

•A warm front is represented as a red line with half circles pointing toward the direction of movement.

Stationary Front

1. a cold and warm air mass meet and neither is strong enough to push ahead

2. it stalls over one location and brings days of precipitation along the front

3. it eventually moves and become a cold or warm front

A stationary front is represented as an alternating cold/warm front symbol pointing in the direction of each front.

High pressureLow pressureAir massSource regionContinentalMaritimePolarTropicalArcticFrontCold frontWarm frontStationary front