Driver's Fabulous Fourth Grade

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4.6 Weather

Anemometer – measures wind speed

Barometer – measures air pressure

Thermometer – measures heat energy

Wind Vane – determines wind direction

Rain Gauge – measures precipitation

Precipitation – rain, snow, sleet, and hail

Cumulus –  Cumulus clouds are fair weather clouds.  They are fluffy and white with flat bottoms and look like big cotton balls in the sky. They are always changing shape and have very large spaces of clear blue sky between them. Precipitation does not usually fall from cumulus clouds.

Cumulonimbus–  This kind of cloud is formed by cumulus clouds that join together. They keep growing until they become so full of moisture, they turn dark and heavy.  Cumulo-nimbus clouds often bring thunderstorms with heavy rains, thunder, and lightning. 

Cirrus– Another fair weather cloud is the cirrus cloud.  Cirrus clouds are feathery and look like commas or wisps of hair high in the sky.  They are made from tiny ice crystals instead of water droplets like other clouds.  No precipitation falls from Cirrus clouds.  Even though they are fair weather clouds, they often indicate that rain or snow will fall within several hours.

Stratus –  Stratus clouds are smooth, gray clouds that cover the whole sky.   They are also the lowest clouds and look like a blanket of gray.  This kind of cloud can stretch for hundreds of miles and can bring light rain and drizzle. 

Front – where two air masses of different temperatures and humidity come together

 A cold front is formed when a cold air mass pushes into a warm air mass.  A cold front will often produce thunderstorms.

A warm front is formed when a warm air mass pushes into a cold air mass.  A warm front will sometimes produce light rain.

 Air Mass – An air mass is a large body of air that has the same temperature and humidity.

Humidity – Amount of water vapor in the air.

A low-pressure area forms when air is warmed.  Low pressure areas usually bring clouds, rain, and wind. 

A high-pressure area forms when air is cooled.  High-pressure areas usually bring dry, clear conditions.