Chapter 13 Section 1 SOL 6.6 f

Air mass= a huge body of air that has similar temperature, humidity and air pressure throughout. Air masses are classified according to 2 characteristics: temperature and humidity. CFU: How are air masses classified?

According to temperature: Tropical or warm air masses form in the tropics and have low air pressure. Polar or cold air masses form in the north and have high air pressure. CFU: Compare and contrast tropical and polar air masses.

According to humidity: Maritime air masses form over water and have a high humidity. Continental air masses form over land and have a low humidity. CFU: Compare and contrast Maritime and Continental air masses.

Maritime Tropical Warm, humid air mass that forms over oceans near the tropics (Gulf of Mexico, Atlantic/Pacific Ocean). In summer, they bring hot, humid weather and form most showers and thunderstorms. In the winter, they bring heavy rain or snow. CFU: Describe a Maritime Tropical Air Mass.

Maritime Polar Cool, humid air mass that forms over the icy cold North Pacific or North Atlantic oceans. Affect the west coast more than the east coast. Often bring fog, rain, and cool temperatures even in the summer months to the west coast. CFU: Describe a Maritime Polar Air Mass.

Continental Tropical Hot, dry air masses that form only in summer over dry areas of Southwest and northern Mexico. Cover a smaller area than other air masses. Bring hot, dry weather to southern Great Plains when they move their usual Northeast. CFU: Describe a Continental Tropical Air Mass.

Continental Polar Large air masses that form over central and northern Canada and Alaska. Bring cool or cold air. In winter, they bring clear, cold, dry air to much of North America-- can bring bitterly cold temperatures with very low humidity. In summer, storms may occur when the polar air masses meet the tropical air masses. CFU: Describe a Continental Polar Air Mass.

Air masses tend to move from West to East. As huge masses of air move across the land and the oceans, they bump into each other. But they do NOT easily mix (think oil and vinegar).

The area where the two air masses meet and do not mix becomes a front. There are four different types: Cold front= cold air overcoming warm air. Warm air is pushed upward and as it rises and cools, clouds are formed. If there is a lot of water vapor in the warm air, heavy rain or snow may fall. They move quickly and can cause abrupt weather such as thunderstorms. CFU: What do you call the area where two air masses meet but don’t mix?

Warm front= warm air overcoming cold air. Can bring clouds, storms and rain. These fronts move slower and can cause rainy weather and fog for several days. Usually leaves behind warm, humid weather. In winter, warm fronts bring snow. CFU: What kind of weather is usually associated with a warm front?

Stationary front=cold and warm battling it out in a “standoff”. Where the two air masses meet, water vapor in the air condenses into rain, snow, fog or clouds. Can bring many days of clouds and precipitation. CFU: Describe a stationary front.

Symbols Cold Front Warm Front Stationary Front Icicles (triangles) Suns (half circles) Both on opposite sides

Occluded front=most complex. Warm air mass sandwiched in between 2 cold air masses which pushes the warm air upward. The 2 cooler air masses meet and warm air is cut off. The weather may turn cloudy, rainy or snowy.

Low pressure areas (also known as a cyclones) bring bad weather such as storms and precipitation and are represented by “L” on a map. High pressure areas (also known as anti-cyclones) bring good weather and are represented by “H” on a map. CFU: What kind of weather do you expect with Low Pressure? High Pressure?

 Low Pressure = Bad Weather L  High Pressure = Good Weather H