Weather.com – Weather Maps

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What is weather? Weather is the condition of Earth’s atmosphere at a certain time and place People talk about weather by describing factors such as temperature, humidity, precipitation, air pressure, wind and visibility Able to observe and MEASURE these six elements

How do we measure temperature? Temperature is a measure of how hot or cold something is A thermometer uses a liquid such as alcohol or mercury to display the temperature. When air gets warmer, the liquid expands and rises in the tube. Cooler air causes the liquid to contract and fill less of the tube.

How do we measure humidity? Humidity is the amount of water vapor in the air Measured using a psychrometer Relative humidity is the amount of water vapor in the air compared to the amount of water vapor needed to reach saturation (dew forms at 100%) Dew point = when water vapor turns into liquid water

How do we measure precipitation? Precipitation is any form of water that falls to Earth’s surface from clouds (rain, snow, hail, and sleet) Measured using a rain gauge or meter stick Air temperature determines which type of precipitation falls to Earth’s surface Two air masses meet; mixing of temperatures produces precipitation and winds (this is called a FRONT)

How do we measure air pressure? Air pressure = the force of which air molecules push on an area We don’t feel the weight because air pushes in all directions Air pressure and density are related; they both decrease with altitude Measured using a barometer Low = storms, High = clear skies

How do we measure air pressure? A high-pressure system forms when an air mass cools; bring dry, clear weather A low-pressure system forms where air masses join; bring precipitation Winds move from an area of high pressure to an area of low pressure; pressure affects wind direction and wind speed

How do we measure air pressure?

How do we measure winds? Wind is air that moves horizontally, or parallel to the ground Caused by the uneven heating of the earth and air pressure differences (convection) Measured with an anemometer (speed) or a wind vane (direction)

How do we measure visibility? Visibility is a measure of the transparency of the atmosphere; how far we can see… Poor visibility can be the result of air pollution or fog; dangerous for travel; ex: dense fog obstructs a driver’s view Measured by a transmissometer

Element of WeatherMeasuring Instrument TemperatureThermometer HumidityHygrometer, Psychrometer PrecipitationRain Gauge, Meter Stick Air PressureBarometer WindAnemometer, Wind Vane VisibilityTransmissometer