Air and Weather p. D12-17

Ingredients of Weather Air Air Wind Wind Moisture Moisture

Greenhouse Effect Heat from the sun that is trapped in Earth’s atmosphere Heat from the sun that is trapped in Earth’s atmosphere This is how the planet is warmed This is how the planet is warmed

Air Masses Huge bodies of air that can cover thousands of miles Huge bodies of air that can cover thousands of miles Two properties-moisture and temperature Two properties-moisture and temperature Moist air masses - form over water Moist air masses - form over water Dry masses - form over land Dry masses - form over land Warm masses- form near the equator Warm masses- form near the equator Cold masses- form near the poles Cold masses- form near the poles

Polar Air Masses Bring cold, dry air Bring cold, dry air

Tropical Air Masses Bring warm, moist air Bring warm, moist air

Weather Fronts When air masses meet, they don’t mix. When air masses meet, they don’t mix. Instead, they form a border called a “front”. Instead, they form a border called a “front”. Active weather happens along these fronts. Active weather happens along these fronts.

Cold Front Forms when cold air catches up with warm air. Forms when cold air catches up with warm air. The cold air pushes the warm air higher up in the atmosphere. The cold air pushes the warm air higher up in the atmosphere. Rising warm air cools and forms clouds. Rising warm air cools and forms clouds. Rain develops. Rain develops. Storms often develop along a cold front. Storms often develop along a cold front.

Warm Front Forms when warm air catches up to cold air. Forms when warm air catches up to cold air. The warm air slides up over the cold air. The warm air slides up over the cold air. Clouds form. Clouds form. Precipitation may fall as the front passes. Precipitation may fall as the front passes. Then the sky clears and the temperatures rise. Then the sky clears and the temperatures rise.

Stationary Front This is a front that stops moving. This is a front that stops moving. It may stay in one place for several days. It may stay in one place for several days. If precipitation is involved, heavy rain or snow may fall. If precipitation is involved, heavy rain or snow may fall.

Clouds Clouds form along fronts. Clouds form along fronts. Therefore, they can help meteorologists predict weather. Therefore, they can help meteorologists predict weather.

Cirrus Clouds High-altitude clouds High-altitude clouds Made of ice crystals Made of ice crystals Winds stretch them into long, wispy horsetail or feather shapes. Winds stretch them into long, wispy horsetail or feather shapes. Mean cool, fair weather. Mean cool, fair weather.

Cumulonimbus Clouds “Storm Clouds” Associated with a cold front Associated with a cold front Towering and dark or gray-white Towering and dark or gray-white Usually mean rain or storms Usually mean rain or storms

Cumulus Clouds Puffy cotton-ball clouds Puffy cotton-ball clouds Seen on clear, warm days Seen on clear, warm days May eventually become cumulonimbus, or storm clouds May eventually become cumulonimbus, or storm clouds

Stratus Clouds Seen on gray, cloudy days Seen on gray, cloudy days Form in low, dark layers Form in low, dark layers May bring rain or snow May bring rain or snow