Fronts & Pressure Systems

Air mass

1. Air mass forms as it sits over a large area of land for many days.

2. The air takes on the characteristics of the land or water below it.

Characteristics of an Air Mass

Air masses are put into categories consisting of two words. The first word describes how much moisture, and the last word describes temp.– Continental: forms over land, air becomes dry– Maritime: forms over water, air becomes moist– Tropical: forms near equator, air becomes

warm– Polar: form far from equator, air becomes cool

Examples of air mass

Where Earth’s surface is cold, the air becomes cold. (polar)

Where Earth’s surface is warm, the air becomes warm. (tropical)

Where Earth’s surface is wet, the air becomes moist. (maritime)

*AS AIR MOVES, IT BRINGS ALONG THE TEMP. AND MOISTURE TO NEW LOCATIONS*

What is my name?

This type of air mass forms over land and near the equator.

This type of air mass forms over water and far away from the equator.

This type of air mass forms over land and far from the equator.

This type of air mass forms over water and near the equator.

FRONTS

When two air masses meet, weather starts to change!

A front is the boundary (space) in between two air masses

Many things can happen when two air masses meet, such as clouds forming, or stormy weather.

Afterward, you experience the temp. and humidity of the air mass that has moved in.

Types of fronts

Cold Front: cold air mass pushes a warm air mass causing the warm air to rise. – As warm air rises it condenses forming tall clouds!

Types of fronts cont…

Warm front: Forms when a warm air mass pushes a cold air mass. Warm air slowly rises over the cold air and the moisture from the warm air condenses into flat clouds. Brings many hours of rain or snow.

http://www.mesoscale.iastate.edu/agron206/animations/05_cnWfronts.html

Types of fronts cont…

Stationary front: occurs when two air masses push against each other without moving. Can become either a warm or cold front depending on which air mass moves first.

Pressure systems

High pressure system- air sinks and spreads out. The spreading air moves slowly clockwise.

Low pressure system- air circles into a low pressure center and moves upward. The motion is counterclockwise and can be very quick.

Pressure system cont..

High pressure system: clear skies and calm air because as air sinks to lower altitudes it warms up a bit. Water droplets evaporate so clouds disappear.

Low pressure system: Air moves up lowering the pressure. The rising air produces stormy weather. This usually happens in between a warm air mass and a cold air mass.

WEATHER MAP