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Water in the AirWater in the Air
Weather is the condition of the atmosphere Weather is the condition of the atmosphere at a certain time and place.at a certain time and place.
The condition is affected by the amount of The condition is affected by the amount of water in the air.water in the air.
The Water CycleThe Water Cycle Water is Water is
constantly constantly being being recycled recycled through through the water the water cycle.cycle.
HumidityHumidity
As water evaporates As water evaporates from lakes oceans and from lakes oceans and plants it becomes plants it becomes water vapor. water vapor.
The amount of water The amount of water vapor in the air is vapor in the air is called humiditycalled humidity..
As the temperature increases, the amount of water vapor the air can hold increases.
Relative HumidityRelative Humidity
Relative Humidity is the amount of water Relative Humidity is the amount of water vapor in the air compared with the maximum vapor in the air compared with the maximum amount of water vapor that the air can hold amount of water vapor that the air can hold at a certain temperatureat a certain temperature
Factors that affect Relative Factors that affect Relative HumidityHumidity
Amount of Water VaporAmount of Water Vapor The more water vapor in The more water vapor in
the air the higher the the air the higher the relative humidity.relative humidity.
The water vapor drops The water vapor drops the relative humidity the relative humidity drops.drops.
TemperatureTemperature The relative humidity The relative humidity
decreases as the decreases as the temperature risestemperature rises and and increases as the increases as the temperature dropstemperature drops
Measuring Relative HumidityMeasuring Relative Humidity
A psychrometer is an instrument that is A psychrometer is an instrument that is used to measure relative humidityused to measure relative humidity..– It consists of two thermometersIt consists of two thermometers: one wet bulb : one wet bulb
thermometer and one dry bulb thermometer.thermometer and one dry bulb thermometer.– The difference in the temperature readings The difference in the temperature readings
between the two thermometers indicates the between the two thermometers indicates the amount of humidity.amount of humidity.
CondensationCondensation
Condensation: the Condensation: the process by which a process by which a gas, such as water gas, such as water vapor, becomes a vapor, becomes a liquid.liquid.
Condensation occurs Condensation occurs when saturated air (air when saturated air (air full of humidity) cools.full of humidity) cools.
Dew PointDew Point
Dew point: the temperature at which a gas Dew point: the temperature at which a gas condenses into a liquid.condenses into a liquid.
Air is saturated at dew pointAir is saturated at dew point
CloudsClouds
A cloud is a collection of millions of tiny A cloud is a collection of millions of tiny water droplets or ice crystals.water droplets or ice crystals.
Clouds form as warm air rises and coolsClouds form as warm air rises and cools
Cumulus CloudsCumulus Clouds Puffy, white clouds that tend to have flat Puffy, white clouds that tend to have flat
bottomsbottoms Form when warm air risesForm when warm air rises Indicate fair weatherIndicate fair weather When they get larger they produce When they get larger they produce
thunderstorms – cumulonimbus cloudsthunderstorms – cumulonimbus clouds Clouds with nimbus or nimbo will produce Clouds with nimbus or nimbo will produce
precipitationprecipitation
Stratus CloudsStratus Clouds
Stratus Clouds form in layersStratus Clouds form in layers Cover large areas and often block out the sunCover large areas and often block out the sun Caused by a gentle lifting of a large body of Caused by a gentle lifting of a large body of
air.air. Nimbostratus clouds are dark stratus clouds Nimbostratus clouds are dark stratus clouds
that produce continuous rain.that produce continuous rain. Fog is a stratus cloud found near theFog is a stratus cloud found near the ground. ground.
Cirrus CloudsCirrus Clouds
Cirrus Clouds are thin feathery white clouds Cirrus Clouds are thin feathery white clouds found at high altitudes found at high altitudes
Cirrus clouds form when the wind is strongCirrus clouds form when the wind is strong They can indicate a change in weather.They can indicate a change in weather.
Clouds and AltitudeClouds and Altitude
Clouds Clouds are are classified classified by the by the altitude altitude that they that they formform
Cloud Classification
Low clouds – have no prefix– Ex. Cumulus, Stratus
Middle clouds – Have the prefix alto – Ex. Altocumulus, Altostratus
High clouds – Have the prefix Cirro– Ex. Cirrostratus, Cirrus
PrecipitationPrecipitation
Precipitation is water in solid or liquid form Precipitation is water in solid or liquid form that falls from the air to the Earth that falls from the air to the Earth
There are four major formsThere are four major forms– RainRain– SnowSnow– SleetSleet– HailHail
RainRain
The most common form of precipitation. The most common form of precipitation. Rain is produced when the water droplets Rain is produced when the water droplets
become a certain size.become a certain size.
Sleet and SnowSleet and Snow
Sleet forms when rain falls through a layer Sleet forms when rain falls through a layer of freezing air. of freezing air.
Snow forms when temperatures are so cold Snow forms when temperatures are so cold that water vapor changes directly to a solid.that water vapor changes directly to a solid.
HailHail
Hail are balls or lumps of ice that fall from Hail are balls or lumps of ice that fall from clouds.clouds.
Hail forms in cumulonimbus cloudsHail forms in cumulonimbus clouds due to due to updrafts freezing the water droplets.updrafts freezing the water droplets.
Air Masses and FrontsAir Masses and Fronts
Changes in weather are caused by the Changes in weather are caused by the movement and interaction of air masses.movement and interaction of air masses.
An air mass is a large body of air where An air mass is a large body of air where temperature and moisture content are temperature and moisture content are similar throughout .similar throughout .
Air MassesAir Masses Air Masses are Air Masses are characterized by characterized by their moisture their moisture content and content and temperature which temperature which is determined by is determined by the area over the area over which the air mass which the air mass formsforms (Source (Source Region)Region)
Types of air masses
Maritime (m) Forms over water; wet Continental ( c ) Forms over land; dry Polar ( P) Forms over polar regions; cold Tropical (T) develops over the tropics: warm
Cold Air MassesCold Air Masses
Cold air masses are Cold air masses are responsible for responsible for bringing extremely cold bringing extremely cold winters. winters.
Warm Air MassesWarm Air Masses
Warm air masses bring Warm air masses bring warm air weather warm air weather systems into the systems into the United States.United States.
This brings milder This brings milder temperatures temperatures
This can also bring This can also bring severe weather during severe weather during the summer months.the summer months.
Fronts Fronts
Front: the boundary between air masses of Front: the boundary between air masses of different densities and usually different different densities and usually different temperaturestemperatures
Four kinds of frontsFour kinds of fronts– Cold frontCold front– Warm frontWarm front– Occluded frontOccluded front– Stationary frontStationary front
Cold FrontsCold Fronts
A cold front forms A cold front forms where cold air moves where cold air moves under warm air under warm air
Move quickly and bring Move quickly and bring thunderstorms, heavy thunderstorms, heavy rain, or snowrain, or snow
Cooler weather follows Cooler weather follows a cold fronta cold front
Warm FrontsWarm Fronts
A warm front forms A warm front forms where warm air moves where warm air moves over colder denser air over colder denser air
Warm air replaces cold Warm air replaces cold airair
Bring drizzly rainBring drizzly rain Followed by clear and Followed by clear and
warm weatherwarm weather
Occluded FrontOccluded Front
An occluded frontAn occluded front forms when a warm air forms when a warm air mass is caught mass is caught between two colder air between two colder air massesmasses
This produces cold This produces cold temperatures and temperatures and large amounts of rain large amounts of rain and snow.and snow.
Stationary FrontsStationary Fronts
Stationary fronts form Stationary fronts form when a cold air mass when a cold air mass meets a warm air meets a warm air mass. mass.
Brings many days of Brings many days of cloudy wet weather.cloudy wet weather.
Weather FrontsWeather Fronts 3737
Be a Weather ForecasterBe a Weather Forecaster
You are planning to travel to Alabama in 2 days. The high temperature there for today is 68º F.
You are planning to travel to Alabama in 2 days. The high temperature there for today is 68º F.
Use the map to help you predict whether the temperature in Alabama will increase, decrease, or stay the same. Explain why you think so.
3838
Be a Weather ForecasterBe a Weather Forecaster
There is a cold front approaching. The temperatures will probably be cooler behind the front.
There is a cold front approaching. The temperatures will probably be cooler behind the front.
Air Pressure and WeatherAir Pressure and Weather
Areas that have lower pressure than the Areas that have lower pressure than the surrounding areas do are called Cyclones.surrounding areas do are called Cyclones.
These areas the air masses come together These areas the air masses come together and riseand rise
Air Pressure and WeatherAir Pressure and Weather
Areas that have high pressure are called Areas that have high pressure are called anticyclones.anticyclones.
Anticyclones are areas where the air moves Anticyclones are areas where the air moves apart and sinksapart and sinks
Air Pressure and WeatherAir Pressure and Weather
By keeping track of the cyclones and By keeping track of the cyclones and anticyclones, meteorologists can predict the anticyclones, meteorologists can predict the weather.weather.
Cyclones cause stormy weatherCyclones cause stormy weather Anticyclones bring dry clear weatherAnticyclones bring dry clear weather
Severe WeatherSevere Weather
ThunderstormsThunderstorms TornadoesTornadoes HurricanesHurricanes Severe weather safetySevere weather safety
ThunderstormsThunderstorms
Thunderstorms Thunderstorms are small intense weather are small intense weather systems that produce strong winds, heavy systems that produce strong winds, heavy rain, lightning, and thunder.rain, lightning, and thunder.
Two atmospheric conditions are needed to Two atmospheric conditions are needed to produce a thunderstorm:produce a thunderstorm:– WarmWarm and moist air near the Earth’s surface and moist air near the Earth’s surface– Unstable atmosphereUnstable atmosphere
LightningLightning LightningLightning is an electric is an electric
discharge that occurs discharge that occurs between a positively between a positively charged area and a charged area and a negatively charged area.negatively charged area.
Can occurCan occur– Between Between two cloudstwo clouds
– Between Earth and a Between Earth and a cloudcloud
– Between two parts of the Between two parts of the same cloudsame cloud
Lightning Lightning
When lightning strikes, energy is released.When lightning strikes, energy is released. Energy is transferred to the air.Energy is transferred to the air. ThunderThunder is the sound that results from the is the sound that results from the
rapid expansion of air along the lightning rapid expansion of air along the lightning strikes.strikes.
Severe ThunderstormsSevere Thunderstorms
Can produce:Can produce:– High windsHigh winds– Hail Hail – Flash floodsFlash floods– TornadoesTornadoes– Lightning that causes Lightning that causes
forest fires and burning forest fires and burning down homesdown homes
TornadoesTornadoes
Tornadoes occur in 1% of all thunderstorms.Tornadoes occur in 1% of all thunderstorms. A A tornado tornado is a small spinning column of air is a small spinning column of air
that has high wind speeds and low central that has high wind speeds and low central pressure and that touches the ground.pressure and that touches the ground.
It starts as a funnel cloud that pokes through It starts as a funnel cloud that pokes through a a cumulonimbus cloud.cumulonimbus cloud.
TornadoesTornadoes
75% of the world’s tornadoes occur in the 75% of the world’s tornadoes occur in the United States.United States.
Occur in spring and early Occur in spring and early summersummer They average 120-180 km/h wind speedThey average 120-180 km/h wind speed
HurricanesHurricanes
HurricanesHurricanes are large rotating tropical are large rotating tropical weather systems that have wind speed of at weather systems that have wind speed of at least 120km/h least 120km/h
They are the most powerful storms on Earth.They are the most powerful storms on Earth. Pacific Ocean hurricanes are called: Pacific Ocean hurricanes are called:
typhoonstyphoons Indian Ocean hurricanes are called: Indian Ocean hurricanes are called:
cyclonescyclones
HurricaneHurricane
Hurricanes happen Hurricanes happen over warm tropical over warm tropical oceans.oceans.
Hurricanes vary in size Hurricanes vary in size from 160 to 1500 km in from 160 to 1500 km in diameter and can diameter and can travel for thousands of travel for thousands of kilometers.kilometers.
How Hurricanes formHow Hurricanes form
Begins as a group of Begins as a group of thunderstormsthunderstorms moving moving over tropical ocean watersover tropical ocean waters
Winds traveling in different directions cause Winds traveling in different directions cause the storm to spinthe storm to spin
It gets its fuel from the contact with the It gets its fuel from the contact with the warm ocean waterswarm ocean waters
The hurricane continues to grow as long as The hurricane continues to grow as long as it is it is over the moist warm sourceover the moist warm source..
Hurricane DamageHurricane Damage
Very destructiveVery destructive Average wind speed is Average wind speed is
120-150 km/h 120-150 km/h Can knock down trees Can knock down trees
and destroy buildingsand destroy buildings Flooding is the most Flooding is the most
destructive part.( storm destructive part.( storm surge).surge).
Weather SafetyWeather Safety
Thunderstorm SafetyThunderstorm Safety Lightning is attracted to Lightning is attracted to
tall objectstall objects Crouch down in open Crouch down in open
areasareas Stay away from waterStay away from water
Tornado SafetyTornado Safety Weather forecast: watch Weather forecast: watch
and warning systemand warning system Watch- tornado may Watch- tornado may
happenhappen Warning- tornado has Warning- tornado has
been spottedbeen spotted Find shelter: basement or Find shelter: basement or
cellarcellar
Weather SafetyWeather Safety
Flood SafetyFlood Safety Weather forecast: Weather forecast:
watches and warning watches and warning systemsystem
Find a high placeFind a high place Always stay out of flood Always stay out of flood
waterswaters
Hurricane SafetyHurricane Safety Watch weather updatesWatch weather updates Evacuate the areaEvacuate the area Have a disaster supply kit Have a disaster supply kit
available with food and available with food and waterwater
Board up windows with Board up windows with plywoodplywood
Stay indoors during the Stay indoors during the stormstorm
Forecasting the WeatherForecasting the Weather
A weather forecast is a prediction of weather A weather forecast is a prediction of weather conditions over the next conditions over the next 3 to 5 days3 to 5 days
A meteorologist is a person who observes A meteorologist is a person who observes and collects data on atmospheric conditions and collects data on atmospheric conditions to make weather predictionsto make weather predictions
Weather-Forecasting TechnologyWeather-Forecasting Technology
High in the skyHigh in the sky– Weather balloons Weather balloons
Measure weather conditions as high as 30 km above Measure weather conditions as high as 30 km above EarthEarth
Measures temperature, air pressure, and Measures temperature, air pressure, and relative relative humidityhumidity
Meteorologists can also measure wind speed and Meteorologists can also measure wind speed and direction direction by tracking the weather balloons.by tracking the weather balloons.
Weather-Forecasting TechnologyWeather-Forecasting Technology Measuring Air Temperature and PressureMeasuring Air Temperature and Pressure
– ThermometerThermometer: a tool used to measure air : a tool used to measure air temperaturetemperature
– BarometerBarometer: an instrument used to measure air : an instrument used to measure air pressurepressure The mercury inside a barometer rises as the air pressure The mercury inside a barometer rises as the air pressure
increasesincreases A rising barometer reading means A rising barometer reading means higher higher pressure and pressure and
possibly possibly clear fair weatherclear fair weather . . Decreasing barometer reading means a Decreasing barometer reading means a lower lower pressure pressure
and possibly and possibly bad weatherbad weather. .
Weather-Forecasting TechnologyWeather-Forecasting Technology
Measuring Wind DirectionMeasuring Wind Direction– Can be measured by using a windsock or wind Can be measured by using a windsock or wind
vanevane WindsockWindsock: is a cone shaped cloth bag open at both : is a cone shaped cloth bag open at both
endsends Wind vaneWind vane: is shaped like an arrow with a large tail : is shaped like an arrow with a large tail
and is attached to a poleand is attached to a pole
Weather-Forecasting TechnologyWeather-Forecasting Technology
Measuring wind speedMeasuring wind speed– AnemometerAnemometer: an instrument used to measure : an instrument used to measure
wind speedwind speed Consists of four cups connected by spokes to a poleConsists of four cups connected by spokes to a pole The cups move The cups move The motion sends an electric current that measures The motion sends an electric current that measures
the wind speedthe wind speed
Weather-Forecasting TechnologyWeather-Forecasting Technology
Radar and SatellitesRadar and Satellites– RadarRadar is used to find the location movement is used to find the location movement
and amount of precipitation and amount of precipitation – Doppler Radar systems on the weather stationDoppler Radar systems on the weather station– Weather Satellites provide the Earth images of Weather Satellites provide the Earth images of
weather systems you see on TV weather weather systems you see on TV weather reportsreports
Weather MapsWeather Maps
National Weather Service (NWS) and National Weather Service (NWS) and National Oceanic and Atmospheric National Oceanic and Atmospheric Administration (NOAA) use information from Administration (NOAA) use information from about about 10001000 weather stations in the US weather stations in the US
This is information from one weather station.This is information from one weather station.
1. Which statement best describes the driving force behind all the weather on Earth, from local weather systems to large-scale storms? A.The Coriolis Effect curves the motion of wind due to the Earth's counter-clockwise rotation.B.The Greenhouse Effect ensures that some of the Sun's heat is always trapped close to the Earth's surface.C.The Sun heats the atmosphere unevenly, so temperatures and pressures are constantly equalizing.D.The ocean holds the heat of the Sun more efficiently and for longer periods than land.
2.. Air masses move from areas with high pressure (such as the poles of the Earth) to areas with low pressure (the equator). The temperature and moisture of an air mass depend on where it is formed.
A continental tropical air mass is _______ and _______. A.warm, moistB.cold, moistC.cold, dryD.warm, dry
3. The amount of water vapor in the air is referred to as A.precipitation.B.condensation.C.humidity.D.temperature.
1. When warm air moves over cold air, a warm front forms. The warm air tends to rise along a gentle slope above the cold air and form layers of clouds.Given this information, which of the following cloud types and weather conditions would most likely result from an incoming warm front?
A.stratus clouds and drizzly rain B.cumulonimbus clouds and thunderstorms C.cumulus clouds and clear weather D.isolated cirrus clouds and clear weather2. Wispy, thin, white clouds can be seen high in the sky on a pleasant day. Which type of clouds are
these? A.stratus B.cumulonimbus C.cirrus D.altostratus3. Sharon woke up on a sunny morning and ate breakfast. Then she looked outside and saw tall,
quickly-forming clouds. The clouds looked ready to rain. When she turned on the TV, she saw just what she thought—a forecast for sudden rains. What most likely caused the change in weather?
A.a warm front overtaking a cold air mass B.lack of wind C.a cold front overtaking a warm air mass D.an expanding warm air mass
1. If the collected information showed that the temperature was 10°C, there was little pressure, and the wind speed was 75 mph, what type of weather would it probably be outside?
A.warm and windy B.warm and sunny C.cold and wet D.cold and windy2. A swirling, high-speed windstorm begins over the ocean. It
contains heavy rains. The wind and rain rotate around a center of low pressure. When the winds inside this tropical cyclone reach 74 mph, which of the following occurs?
A.hurricane B.tropical depression C.tropical storm D.thunderstorm3. A local barometer reading on a local weather forecast was 29.8 mm
and falling. What type of weather conditions are most likely to occur?A. clear and coolB. clear and warm C. fair skies D. cloudy skies