Greenville Downtown Airport - GMU
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Weather Affects Flying Sign
Weather Instruments Sign
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Weather Instruments Sign
Weather Instruments

Weather describes the atmosphere at a particular point in time. It includes conditions such as wind, temperature, cloudiness, moisture, precipitation (rain, sleet, snow, and hail), and air pressure.

Describing Weather
Scientists who study weather are meteorologists. They measure and record weather conditions so they can identify patterns over time and make forecasts (predictions) about future weather. Pilots check weather forecasts frequently to determine flight conditions.

Wind is moving air.
Wind direction is the direction the wind blows from. Wind direction is determined by a wind sock or weather vane. Wind speed is how fast or slow the wind is blowing. Wind speed is measured with an anemometer. It can be measured in different units, such as miles per hour or knots (nautical miles per hour).
1 knot = 1 nautical mile per hour = 6076 feet per hour
1 mph = 1 mile per hour = 5280 feet per hour
1 knot = 1.151 miles per hour

Moisture in the air is referred to as humidity.
Humidity is measured with a sling psychrometer.

Precipitation is when water from the atmosphere falls to the Earth in the form of rain, snow, sleet, or hail. Rainfall is measured with a rain gauge.

Air Pressure
Air pressure is the weight of air pressing down on Earth. Air pressure can change from place to place, and this causes air to move, flowing from areas of high pressure to areas of low pressure. Air pressure is measured with a barometer; air pressure is sometimes referred to as barometric pressure.

Temperature is how hot or cold something is. Temperature is measured with a thermometer. It can be measured in different units such as Fahrenheit or Celsius.

Where does weather occur?
Weather occurs in the atmosphere near Earth’s surface. The atmosphere is made up mostly of nitrogen (79%) and oxygen (20%). The other 1% is argon, carbon dioxide, water vapor, and other trace gases.  

The atmosphere is divided up into layers based on temperature.  This graph shows the layers of the atmosphere and how the temperature changes in the different layers. It also shows the air pressure in the different layers. Most of the Earth’s weather occurs in the Troposphere.

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