1. Chapter 5
Weather

2. Lesson 1
Describing Weather

3. What is weather?
The atmospheric conditions, along with short- term changes, of a certain place at a certain time
Includes temperature and rainfall
Weather helps you decide what to wear that day
Air temperature, air pressure, wind speed, wind direction, humidity, cloud cover, and precipitation
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4. What is temperature?
The average kinetic energy of molecules in the air
Varies with time of day, season, location, and altitude
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5. What is air pressure?
The pressure that a column of air exerts on the air or a surface below it
Decreases as altitude increases
Barometric pressure – measured in millibars (mb)
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6. What is wind?
Air moving from areas of high pressure to areas of low pressure
Measured using an anemometer
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7. What is humidity? The amount of water vapor in the air
Measured in grams of water per cubic meter of air
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8. What is relative humidity?
The amount of water vapor present in the air compared to the maximum amount the air can hold
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9. What is dew point?
The temperature at which air is fully saturated because of decreasing temperature while holding the amount of moisture constant
(when air is full of water because temperature decreased and some of the vapor condenses)
Dew is the water droplet you see on leaves when water vapor condenses
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10. What are clouds or fog?
Condensed water droplets or ice crystals in the air
Stratus clouds – flat, white, and layered
Cumulus clouds – fluffy and piled up
Cirrus clouds – wispy and high in the air
What about fog?
A cloud that forms near the Earth’s surface
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11. What is precipitation?
Water in liquid or solid form falling to Earth from the atmosphere
Rain – droplets of water
Snow – frozen crystals
Sleet – frozen or freezing rain
Hail – large pellets of ice
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12. What is the water cycle?
The series of natural processes by which water continually moves among oceans, land, and the atmosphere
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13. Lesson 2
Weather Patterns

14. What is a high-pressure system?
A large body of circulating air with high pressure at its center
Cold, dense air sinks and pushes air away
Weather is usually fair and sunny
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15. What is a low-pressure system?
A large body of circulating air with low pressure at its center
Less dense air rises and cools
Weather is usually cloudy and can include precipitation
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16. What are air masses?
Large bodies of air that have uniform temperature, humidity and pressure
Form when high pressure systems stay in an area for several days
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17. Types of Air Masses Arctic – form in the arctic
Continental polar – form over cold land
Maritime polar – form over cold water
Continental tropical – form over warm land
Maritime tropical – form over warm water
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18. Air Masses Continental Maritime Polar Cold land Cold water Tropical
Warm land
Warm water

19. What is a front? A boundary between two air masses
Cold – cold air pushing under warm air; thunderstorms common
Warm – warm air pushing over cold air; wide blanket of clouds
Stationary – two air masses not moving
Occluded – a cold front passing a warm front
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20. Severe Weather Thunderstorms
Forms from cumulus clouds that grow tall into cumulonimbus
Lots of lightning caused by ice crashing into each other
Strong wind and rain
Three stages – cumulus, mature, and dissipation
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21. What are tornadoes?
A violent, whirling column of air in contact with the ground
Usually only last a few minutes, but have winds strong enough to send large objects flying
Form in thunderstorms when parts of an updraft swirl toward the ground in a funnel cloud
When the funnel cloud reaches the ground it becomes a tornado
Measured by the Fujita scale (F1 – F5)
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22. What is a hurricane?
An intense tropical storm with winds over 119 km/h
Have a circular shape based on air movement
Warm, moist air rises forming an area of low pressure
As more air rises, it strengthens into a tropical depression (37-62 km/h) and then a tropical storm (63 km/h)
Damage comes from winds and flooding
Also called typhoons or cyclones
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23. What is a blizzard?
A violent winter storm characterized by freezing temperatures, strong winds, and blowing snow
Snow can reduce visibility
Ice storms can cause structures to break under the weight of ice
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24. Lesson 3
Weather Forecasts

25. Measuring the Weather Who measures weather? A meteorologist
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26. What is a surface report?
It describes a set of weather measurements made on Earth’s surface
What is an upper-air report?
It describes wind, temperature, and humidity above Earth’s surface
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27. Satellite and Radar
Satellites can provide information about clouds and heat
What is Doppler radar?
Specialized radar that detects precipitation and wind speed
This is useful during severe weather
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28. Weather Maps
Maps of station models can help provide information on weather over a large area
They can show fronts and other patterns
What are isobars?
Lines that connect all places on a map that have the same pressure
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29. Predicting the Weather
What are computer models?
Detailed computer programs that solve a set of complex math formulas
They are used to predict temperature, wind, and cloud formation
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