3.1 Weather changes as air masses move.
An air mass is a large volume of air in which temperature and humidity are nearly the same in different locations at the same time. An air mass can cover many thousands of square kilometers.
An air mass forms when the air over a large region of Earth sits in one place for many days. The air gradually takes on the characteristics of the land or water below it.
Where two different air masses meet it forms a front. As one air mass pushes another, some of the air at the boundary will by pushed upward. Clouds can form in this rising air. The weather often becomes cloudy or stormy as a front passes. Afterward, you experience the temperature and humidity of the air mass that has moved in.
Different types of fronts produce different patterns of weather.
Cold Front:
Cold Front:
- moves in quickly
- pushes warmer air ahead of it upward
- Brief heavy storms are likely
- After the storm the air is cooler
Warm Front:
- move more slowly than cold fronts
- can bring many hours of steady rain or snow. After the front passes, the air is warmer.
Stationary Front:
- occurs when air masses first meet or when a cold or warm front stops moving.
- when the front starts moving, it becomes a warm front if the warm air advances and pushes the cold air. If the cold air moves forward instead, the front becomes a cold front.
High Pressure System
A high pressure system is formed when air moves all the way around a high-pressure center. Most high-pressure systems are large and change slowly. When a high-pressure system stays in one location for a long time, an air mass may form. The air and resulting air mass-can be warm or cold, moist or dry.
A high pressure system is formed when air moves all the way around a high-pressure center. Most high-pressure systems are large and change slowly. When a high-pressure system stays in one location for a long time, an air mass may form. The air and resulting air mass-can be warm or cold, moist or dry.
Low Pressure System
A low-pressure system is a large weather system that surrounds a center of low pressure. It begins as air moves around and inward toward the lowest pressure and then up to higher altitudes. The upward motion of the air lowers the air pressure further, and so the air moves faster. The pattern of motion strengthens into a low-pressure weather system. The rising air produces stormy weather.
A low-pressure system is a large weather system that surrounds a center of low pressure. It begins as air moves around and inward toward the lowest pressure and then up to higher altitudes. The upward motion of the air lowers the air pressure further, and so the air moves faster. The pattern of motion strengthens into a low-pressure weather system. The rising air produces stormy weather.