Weather Patterns Earth Science Chapter 17. Air mass Huge body of air with similar temperature, humidity, and air pressure at any height Can be huge Classified

Weather Patterns

Earth Science Chapter 17

Earth Science chapter 17 2

Air mass

• Huge body of air with similar temperature, humidity, and air pressure at any height

• Can be huge• Classified by temperature and humidity

• Tropical or polar• Temperature

• Maritime or continental• humidity


Maritime Tropical

• Warm and humid• Form over tropical oceans• Then move across land• Hot and humid in summer• Bring heavy rain or snow in winter


Maritime Polar

• Cool and humid• Form over polar oceans• Affect west coast more than east coast• Bring fog, rain, and cool temperatures


Continental Tropical

• Hot and dry• Form over dry land areas – southwest and

Mexico• Smaller than other air masses• Bring hot, dry weather


Continental Polar

• Cool and dry• Form over Canada and Alaska• Can bring bitterly cold and dry weather in

winter• Milder in summer• Cause storms when colliding with maritime

tropical masses


Air mass movement

• Caused by prevailing westerlies and jet streams (in US)

• Prevailing westerlies push from west to east• Jet streams push from west to east faster


Fronts

• Air masses don’t easily mix• Front – boundary where air masses meet


Discuss

• What two characteristics are used to classify air masses?

• What are the four types of air masses?• What is a front?


Cold fronts

• Rapidly moving cold air mass runs into a slowly moving warm air mass – from opposite directions

• Denser cold air slides under• Warm air pushed up and cooled

• Causes water vapor to condense• Clouds form• Can cause heavy rain or snow

• Cause abrupt weather changes• After front moves through, usually clear skies,

cooler, and wind shifts


Warm fronts

• Fast-moving warm air mass overtakes a slowly moving cold air mass

• Moving same direction• Warm air moves over

• Light rain or snow• Cloudy skies

• After front usually warm and humid


Stationary fronts

• Warm and cold meet, but don’t move each other

• From opposite directions• Rain, snow, fog, or clouds• Can last many days


Occluded fronts

• Most complex• Warm air mass caught between two cold air

masses• Warm air moves up• Cold air masses may mix• Surface temperature becomes cool• Cloudy, rain, or snow


Cyclones

• Air at a frontal boundary gets distorted, bends and swirls• Caused by mountains or jet stream

• Swirling area of low pressure• Winds spiral in• Spin counterclockwise in northern

hemisphere• Clouds, wind, and precipitation


Anticyclones

• High pressure and dry air• Winds spiral out• Spin clockwise in northern hemisphere• Dry, clear weather


Discuss

• Name the four types of fronts and they types of weather each one brings.

• Compare and contrast cyclones and anticyclones.

• What type of front would most likely be responsible for several days of rain and clouds?


Storm

• Violent disturbance in atmosphere• Sudden changes in air pressure

• Rapid air movements


Thunderstorms

• Small storm with heavy precipitation and frequent lightning and thunder

• Form in cumulonimbus clouds (thunderheads)

• Heavy rain, maybe hail


Lightning and thunder

• Lightning• Sudden spark between areas of different

electrical charge• Within a cloud• Cloud to cloud• Cloud to ground

• Thunder• Lightning heats air rapidly and makes it expand

and explode


Thunderstorm damage

• Flooding• Overloaded rivers/streams• Saturated ground• Urban areas with little access to ground

• Lightning damage• Hail damage


Thunderstorm safety

• Safer inside• Avoid touching electrical appliances or

plumbing• Avoid metal or bodies of water• If outside, find a low area away from

anything tall


Tornadoes

• Rapidly whirling, funnel-shaped cloud• Usually brief, but can be deadly• Wind speeds up to 500 km/hr• Most often form in thunderheads when cold

air and warm air meet


Tornado damage

• Strong winds and flying debris• Low pressure sucks object up into cloud

• May deposit many miles away

• Unpredictable path• Tornadoes ranked from F0 to F5 by damage


Tornado safety• Tornado watch – conditions are favorable

for tornado formation• Watch for thunderstorms and stay near radio,

TV or internet for weather info

• Tornado warning – a tornado has been seen• Get to a safe place ASAP• Basement of a well-built building• Middle of ground floor, away from windows

and doors• Lie flat in a ditch


Discuss

• What weather conditions are most likely to produce tornadoes?

• Why do tornadoes occur most often in “tornado alley”?

• What safety precautions should be taken in a thunderstorm?

• What safety precautions should be taken in a tornado?


Hurricane

• Tropical cyclone with winds of 119 km/hr or higher

• About 600 km across


Hurricane formation

• Forms as a low-pressure area over warm ocean water

• Warm air from water rises and forms clouds, draws more air up

• Has bands of very high winds and heavy rains

• Strongest winds around calm “eye”


Hurricane motion

• Last longer than most storms – a week or more

• Form in Atlantic and move towards Caribbean and southeastern US – carried by trade winds

• Lose energy when hit land – no more warm, moist air to draw up• Can cause several days of heavy rain over land


Hurricane damage

• High waves, severe flooding, and wind damage

• Low pressure and high winds raise ocean level up to six meters• Storm surge – dome of water that hits coast

where hurricane lands• Major flooding and erosion


Hurricane safety

• Hurricane watch – possible within 36 hours• Prepare to evacuate

• Hurricane warning – expected within 24 hours• Leave area immediately if told to evacuate• If you stay in a house, move away from

windows


Winter storms

• Precipitation falls as snow if the air is below freezing all the way down to the ground• Heavy snow – can block roads• Extreme cold – can damage crops and freeze

pipes• High winds – reduce visibility and break trees

and power lines

• For safety – find shelter from wind and try to stay dry


Lake – effect snow

• Falls south and east of Great Lakes• Cold dry air moves across warmer water

and gets humid• Moves across land, cools, and can’t hold all

the humidity


Discuss

• How do hurricanes form?• What is lake-effect snow?• What should you do if you are caught in a

snowstorm?


Weather Forecasting

• First, make observations and collect data• Simple observations

• Watch the clouds• Cumulus clouds growing taller may mean a

thunderstorm• High thin cirrus clouds may mean an approaching

warm front


More complex data

• Meteorologists use• Local observers• Radar• Instruments in balloons, satellites, and global

weather stations• Mostly from national weather service


Weather Technology

• Weather balloons• Carry instruments into lowest layers of

atmosphere• Measure temperature, air pressure, and

humidity• Weather satellites

• Orbit in uppermost atmosphere• Send images back to Earth• Can show temperature, humidity, solar

radiation, wind speed, and wind direction


More Weather Technology

• Automated weather stations• Surface locations• Temperature, air pressure, relative humidity,

rainfall, wind speed, and wind direction

• Computer forecasts• Process large amounts of data quickly• Make predictions using mathematical models


Discuss

• What tools do meteorologists rely on to forecast the weather?

• How does the large amount of weather data gathered by various modern technologies affect the accuracy of weather forecasts?

• What types of weather information is gathered by satellites?


Weather Service maps

• Assemble data from all over the country• Show temperature, wind speed and

direction, fronts, air pressure• Isobars – lines connecting areas with the

same air pressure• Isotherms – lines connecting areas with the

same temperature


Newspaper Weather Maps

• Simpler than weather service maps• Use standard symbols


Limits of weather forecasts

• A small change in one part of the atmosphere can cause a large change in the forecast a few days later• The butterfly effect


Doppler Radar

• Uses the Doppler effect• Uses changes in radio waves as they reflect off

moving objects

• Radio waves bounce off particles in the air, like raindrops, snowflakes, hail, and dust


Doppler radar effectiveness

• Can give people more advance warning for storms like tornadoes

• Can be blocked by mountains or buildings• Doesn’t always pick up drizzle• Dust can interfere with it

• Meteorologists must use more than just Doppler to forecast the weather


Discuss

• According to the weather map on page 604, what is the weather like in Chicago? How might it change in a few hours?

Documents

Weather Patterns Earth Science Chapter 17. Air mass Huge body of air with similar temperature, humidity, and air pressure at any height Can be huge Classified