2Water in the AirWeather is the condition of the atmosphere at a certain time and place.The condition is affected by the amount of water in the air.
3The Water CycleWater is constantly being recycled through the water cycle.
4HumidityAs water evaporates from lakes oceans and plants it becomes water vapor.The amount of water vapor in the air is called humidity.As the temperature increases, the amount of water vapor the air can hold increases.
5Relative HumidityRelative Humidity is the amount of water vapor in the air compared with the maximum amount of water vapor that the air can hold at a certain temperature
6Factors that affect Relative Humidity Amount of Water VaporTemperatureThe more water vapor in the air the higher the relative humidity.The water vapor drops the relative humidity drops.The relative humidity decreases as the temperature rises and increases as the temperature drops
7Measuring Relative Humidity A psychrometer is an instrument that is used to measure relative humidity.It consists of two thermometers: one wet bulb thermometer and one dry bulb thermometer.The difference in the temperature readings between the two thermometers indicates the amount of humidity.
13Cumulus Clouds Puffy, white clouds that tend to have flat bottoms Form when warm air risesIndicate fair weatherWhen they get larger they produce thunderstorms – cumulonimbus cloudsClouds with nimbus or nimbo will produce precipitation
14Stratus Clouds Stratus Clouds form in layers Cover large areas and often block out the sunCaused by a gentle lifting of a large body of air.Nimbostratus clouds are dark stratus clouds that produce continuous rain.Fog is a stratus cloud found near the ground.
15Cirrus CloudsCirrus Clouds are thin feathery white clouds found at high altitudesCirrus clouds form when the wind is strongThey can indicate a change in weather.
16Clouds and AltitudeClouds are classified by the altitude that they form
17Cloud Classification Low clouds – have no prefix Ex. Cumulus, StratusMiddle clouds – Have the prefix altoEx. Altocumulus, AltostratusHigh clouds – Have the prefix CirroEx. Cirrostratus, Cirrus
18PrecipitationPrecipitation is water in solid or liquid form that falls from the air to the EarthThere are four major formsRainSnowSleetHail
19Rain The most common form of precipitation. Rain is produced when the water droplets become a certain size.
20Sleet and SnowSleet forms when rain falls through a layer of freezing air.Snow forms when temperatures are so cold that water vapor changes directly to a solid.
21Hail Hail are balls or lumps of ice that fall from clouds. Hail forms in cumulonimbus clouds due to updrafts freezing the water droplets.
22Air Masses and FrontsChanges in weather are caused by the movement and interaction of air masses.An air mass is a large body of air where temperature and moisture content are similar throughout .
23Air MassesAir Masses are characterized by their moisture content and temperature which is determined by the area over which the air mass forms (Source Region)
24Types of air masses Maritime (m) Forms over water; wet Continental ( c ) Forms over land; dryPolar ( P) Forms over polar regions; coldTropical (T) develops over the tropics: warm
25Cold Air MassesCold air masses are responsible for bringing extremely cold winters.
26Warm Air MassesWarm air masses bring warm air weather systems into the United States.This brings milder temperaturesThis can also bring severe weather during the summer months.
27FrontsFront: the boundary between air masses of different densities and usually different temperaturesFour kinds of frontsCold frontWarm frontOccluded frontStationary front
28Cold Fronts A cold front forms where cold air moves under warm air Move quickly and bring thunderstorms, heavy rain, or snowCooler weather follows a cold front
29Warm FrontsA warm front forms where warm air moves over colder denser airWarm air replaces cold airBring drizzly rainFollowed by clear and warm weather
30Occluded FrontAn occluded front forms when a warm air mass is caught between two colder air massesThis produces cold temperatures and large amounts of rain and snow.
31Stationary FrontsStationary fronts form when a cold air mass meets a warm air massBrings many days of cloudy wet weather.
32Air Pressure and Weather Areas that have lower pressure than the surrounding areas do are called Cyclones.These areas the air masses come together and rise
33Air Pressure and Weather Areas that have high pressure are called anticyclones.Anticyclones are areas where the air moves apart and sinks
34Air Pressure and Weather By keeping track of the cyclones and anticyclones, meteorologists can predict the weather.Cyclones cause stormy weatherAnticyclones bring dry clear weather
35Severe Weather Thunderstorms Tornadoes Hurricanes Severe weather safety
36ThunderstormsThunderstorms are small intense weather systems that produce strong winds, heavy rain, lightning, and thunder.Two atmospheric conditions are needed to produce a thunderstorm:Warm and moist air near the Earth’s surfaceUnstable atmosphere
38LightningLightning is an electric discharge that occurs between a positively charged area and a negatively charged area.Can occurBetween two cloudsBetween Earth and a cloudBetween two parts of the same cloud
39Lightning When lightning strikes, energy is released. Energy is transferred to the air.Thunder is the sound that results from the rapid expansion of air along the lightning strikes.
40Severe Thunderstorms Can produce: High winds Hail Flash floods TornadoesLightning that causes forest fires and burning down homes
41Tornadoes Tornadoes occur in 1% of all thunderstorms. A tornado is a small spinning column of air that has high wind speeds and low central pressure and that touches the ground.It starts as a funnel cloud that pokes through a cumulonimbus cloud.
47HurricanesHurricanes are large rotating tropical weather systems that have wind speed of at least 120km/hThey are the most powerful storms on Earth.Pacific Ocean hurricanes are called: typhoonsIndian Ocean hurricanes are called: cyclones
48Hurricane Hurricanes happen over warm tropical oceans. Hurricanes vary in size from 160 to 1500 km in diameter and can travel for thousands of kilometers.
49How Hurricanes formBegins as a group of thunderstorms moving over tropical ocean watersWinds traveling in different directions cause the storm to spinIt gets its fuel from the contact with the warm ocean watersThe hurricane continues to grow as long as it is over the moist warm source.
51Hurricane Damage Very destructive Average wind speed is 120-150 km/h Can knock down trees and destroy buildingsFlooding is the most destructive part.( storm surge).
52Weather Safety Thunderstorm Safety Tornado Safety Lightning is attracted to tall objectsCrouch down in open areasStay away from waterWeather forecast: watch and warning systemWatch- tornado may happenWarning- tornado has been spottedFind shelter: basement or cellar
54Weather Safety Flood Safety Hurricane Safety Weather forecast: watches and warning systemFind a high placeAlways stay out of flood watersWatch weather updatesEvacuate the areaHave a disaster supply kit available with food and waterBoard up windows with plywoodStay indoors during the storm
56Forecasting the Weather A weather forecast is a prediction of weather conditions over the next 3 to 5 daysA meteorologist is a person who observes and collects data on atmospheric conditions to make weather predictions
57Weather-Forecasting Technology High in the skyWeather balloonsMeasure weather conditions as high as 30 km above EarthMeasures temperature, air pressure, and relative humidityMeteorologists can also measure wind speed and direction by tracking the weather balloons.
59Weather-Forecasting Technology Measuring Air Temperature and PressureThermometer: a tool used to measure air temperatureBarometer: an instrument used to measure air pressureThe mercury inside a barometer rises as the air pressure increases
60Weather-Forecasting Technology Measuring Wind DirectionCan be measured by using a windsock or wind vaneWindsock: is a cone shaped cloth bag open at both endsWind vane: is shaped like an arrow with a large tail and is attached to a pole
61Weather-Forecasting Technology Measuring wind speedAnemometer: an instrument used to measure wind speedConsists of four cups connected by spokes to a poleThe cups moveThe motion sends an electric current that measures the wind speed
63Weather-Forecasting Technology Radar and SatellitesRadar is used to find the location movement and amount of precipitationDoppler Radar systems on the weather stationWeather Satellites provide the Earth images of weather systems you see on TV weather reports
65Weather MapsNational Weather Service (NWS) and National Oceanic and Atmospheric Administration (NOAA) use information from about 1000 weather stations in the USThis is information from one weather station.