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Name ________________________________________________ SOL 4.6 WEATHER Study Guide Temperature is the measurement of the amount of heat of an object The more directly the sunlight hits the earth’s surface, the higher the temperature will be. The faster air molecules move the higher their temperature. A thermometer measures temperature. Warm air rises. Cold air is heavier and sinks down to the ground. Air Pressure and Wind Air pressure is the force with which air presses against the earth’s surface. Wind is air moving from a high pressure area to a low pressure area. A barometer measures air pressure. An anemometer measures wind speed. A wind vane measures the direction of the wind. High pressure areas have fair weather. Low pressure areas have stormy weather. Air pressure is higher closer to the ground. Mountains have lower air pressure. Valleys have higher air pressure. Clouds No two clouds are exactly the same. Clouds are made up of tiny water droplets. A cloud that forms close to the ground is called fog. A stratus cloud forms in layers across the sky. It usually brings rain. A cumulus cloud is puffy and white. It usually brings fair weather. A cirrus cloud is thin and made of ice crystals. It usually brings fair weather. It is formed high in the sky. A cumulonimbus cloud is a storm cloud. It brings rain or snow. It is also called a thunderhead. Humidity and Precipitation Humidity is the amount of moisture in the air. A hygrometer measures humidity. Precipitation falls from the clouds. Snow, sleet, rain, and hail are examples. It is measured using a rain gauge. Fronts, air masses, and weather maps An air mass is a large amount of air that has the same temperature and humidity. The place where two air masses meet is called a front. A warm front forms when warmer air pushes against colder air. It is shown on a weather map with a red bumpy line. A cold front forms when colder air pushes against warmer air. It is shown on a weather map as a blue pointed line. Air masses and fronts move from west to east in the United States. Thunderstorms, Hurricanes, and Lightning Lightning is caused by electrical charges that build up inside a cloud. A hurricane is a violent storm that develops over tropical water. The eye of the hurricane is a calm region in its center. A tornado is a funnel shaped cloud with high winds. A hurricane is much bigger than a tornado. It also has stronger winds and lasts longer than a tornado.