4.2 Weather Patterns Pages 173-177

Pressure Systems Air pressure is the force of air on the surface. High pressure air always moves toward areas of Low Pressure Hot Air Rises Cold Air Sinks

High Pressure System low pressure is on either side of the HP 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. High Pressure System

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 Low Pressure System

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

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

Air masses are given a two word name that describes it’s moisture and temperature Naming Air Masses

Moisture/Humidity (1st word) continental (c) forms over land – dry maritime (m) forms over water – wet/humid/moist

forms in warmer regions, hot Polar – (P) forms in cold regions – cold 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 Front 1. 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 Front 1. 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.

Occluded Front Cold fronts move faster than warm fronts. 2. A fast moving cold front catches up with a slow moving warm front 3. Cold air pushes right through and pushes warm air out of the way. 4. Usually brings precipitation. Occluded Front

An occluded front is represented as cold and warm front symbols on the same side pointing in the direction of the front