Download - Understanding Weather
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Understanding Weather
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Weather FactorsWeather – refers to the state of the atmosphere at a specific time and place. It occurs in the troposphere.
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5 Factors that affect WeatherAir TemperatureWindHumidityRelative HumidityDew Point
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SunProvides almost all of Earth’s energy
Causes evaporationIt is a source of heat energyEarth’s surface absorbs the Sun’s heat
The Sun provides the energy that drives Earth’s weather
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Air TemperatureHigh Temp. – air molecules move fast and it feels warm
Temperature is a measure of the average amount of motion of molecules.
Low Temp. – air molecules move slower and it feels cold
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Warm AirLow Pressure
Cold AirHigh Pressure
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Thermometer – instrument used to measure temperature
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WindAir moving in a specific direction
Wind results because air moves from areas of high pressure( cold air) to areas of low pressure(warm air).
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Instruments to Measure WindWind Direction is measured with a wind vaneWind Speed is measured with an anemometer
Wind Vane Anemometer
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HumidityThe amount of water vapor in the airMore water vapor can be present in
warmer temperaturesLess water vapor is present in cooler
temperaturesWhen enough water vapor is present
in air for condensation to take place, the air is Saturated
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Relative HumidityIs a measure of the amount of water vapor
present in the air compared to the amount needed for saturation at a specific temperature.
Weather forecasters report the amount of moisture in the air as Relative Humidity
If you hear the forecaster say that the relative humidity is 50%, it means that the air contains 50% of the water needed for the air to be saturated.
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Psychrometer – instrument to measure humidity. Uses the difference in readings between two thermometers, one having a wet bulb and the other having a dry bulb, to measure the moisture content or relative humidity of air
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Dew PointThe temperature at which air is
saturated and condensations forms.Dew point changes with the amount
of water vapor in the air.Air near the ground cools to its dew
point, water vapor condenses and forms dew,
Frost may form when temperatures are near 0⁰ C (32⁰ F)
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CloudsForm as warm air is forced upward,
expands, and coolsWhen relative humidity reaches
100% tiny water droplets begin to form(condensation)
Billions of droplets attach to particles in the air to form a cloud
3 main types of clouds: Stratus, Cumulus, and Cirrus.
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StratusForms at low altitudesClouds of layers, or smooth, even sheetsStratus clouds near the ground are called FOGAssociated with fair weather or rain or snow
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CumulusClouds are masses of puffy, white clouds,
often flat basesAssociated with fair weather or
thunderstorms
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Cumulonimbus = Thunderstorms
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CirrusCirrus clouds are the highest clouds. They usually mean fair weather. They look white and feathery and made of
ice
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PrecipitationWater falling from the clouds4 different forms: Rain, Snow, Sleet, and Hail
Air temperatures determine which it will be.
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Rain and SnowRain dropsfalling in Temps Above Freezing.
Snow formsWhen theTemps areSo cold thatWater vaporTurns intoA solid.
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SleetSleet forms whenRaindrops pass throughA layer of freezing Air near the surface.
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HailHailstones are pellets Of ice that form insideA cloud.
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The relative humidity of air helps determine whether a location will have a dry day or experience some form of precipitation.