1. Section 2 and 3 Weather Patterns
Chapter 13
Section 2 and 3
Weather Patterns

2. Pressure Systems
Air pressure = weight of the molecules in a large mass of air. (2 TYPES)
1) HIGH pressure system
Cool air masses
More “weight” because cool => molecules are closer together. (Sinking air at center.)
Air moves clockwise – away from center.
Associated w/ clear skies and fair weather.

3. Pressure Systems cont. Warm air masses.
2) Low Pressure System
Warm air masses.
Less dense => air molecules are farther apart.
Air moves counter clockwise – towards the center.
Air rises at center which then cools and water vapor condenses.
Associated w/ cloudy weather and sometimes precip.
*Know how to compare and contrast the two!!!

4. (areas of air pressure).
Always remember …
Winds blow from
HIGH to LOW
(areas of air pressure).

5. Air Mass: large body of air that has uniform temp
Air Mass: large body of air that has uniform temp., humidity, and pressure
*Takes on the temp, etc. of the surface where it formed.
Ex. Air mass over tropics will be warmer than an air mass that develops over the North Pole.
Ex. Air mass that develops over land is dryer than an air mass that develops over water.

6. 5 ways AIR MASSES are classified ~
1) Arctic Air Masses = bitterly cold, dry air.
Form Siberia & Arctic – kind that causes neg. temps.
2) Continental Polar Air Masses = fast moving, cold & dry.
Cold temps in winter & cool weather in summer.
3) Maritime Polar Air Masses = cold & humid.
Bring cloudy, rainy weather.
4) Continental Tropical Air Masses = hot & dry.
Bring clear skies and high temps.
5) Maritime Tropical Air Masses = Hot & humid.
Summer – hot & humid
Winter – heavy snowfall

7. Air masses not constant …
Change as they move from land to ocean and from ocean to land.
Remember: if over land (“continental”) = dry
if over ocean (“maritime”) = moisture
if POLAR = cold temp
if TROPICAL = warm temp

8. 4 kinds!!! Pictures on P. 462 – 463 FRONTS
Definition: Boundary between 2 air masses of different density, moisture, or temp.
4 kinds!!! Pictures on P. 462 – 463

9. Cold air advances toward warm air. Cold air wedges under warm air.
1.) Cold Front:
Cold air advances toward warm air.
Cold air wedges under warm air.
(think snow plow)
Represented by blue lines w/ triangles on weather map (draw)
(When temp diff is large, thunderstorms or tornados can form.)
*Brings drop in temp, clouds, precip,
wind & severe storms

10. 2.)Warm Front:
Form when lighter, warmer air advances over heavier, colder air
Represented by red lines w/ semicircles on weather
* Brings rising temps,
steady rain & a change in wind direction.

11. 3.)Occluded Front *Need 3 air masses.
*Usually 2 cold fronts close off a warm front from the surface.
*Usually precip

12. 4.)Stationary Front
Boundary between air masses stops advancing. (They are stuck – days of precip.)
Represented by alternating blue and red lines w/ triangles and semicircles.

13. Severe Weather Heavy rains, lightning, thunder, hail, etc.
Thunderstorms:
Heavy rains, lightning, thunder, hail, etc.
Occur in Warm, moist air masses and along fronts (boundaries!!!)
Sinking, rain-cooled air and strong updrafts of warmer air cause the strong winds.
To be “severe” – winds 89 m/hr or more.
Damage:
Flash Floods – happen w/out warning
Hail and / or Wind Damage
Lightning strikes

14. Lightning: Sinking, rain-cooled air and strong updrafts of warmer air
Cause clouds to become charged.
Forms a current between these charged clouds and ground or object
Pos. and Neg. charges join ….
Makes the FLASH*

15. THUNDER Results from: the rapid heating of air around the lightning
then it rapidly cools and contracts.
Makes a sound wave = thunder

16. Types of Severe Storms Produced by thunderstorms
1.)Tornado:
Produced by thunderstorms
Whirling, violent wind that moves over narrow strip of land
Funnel Cloud – in air
Tornado – called this when it touches ground!!
Fujita Classification: F1 – F4 moderate damage, F5 incredible damage!

17. 2.)Hurricanes: (150,000 x larger than tornado)
*The most POWERFUL storm.
*Large, swirling low-pressure formed over the Atlantic Ocean (Called Typhoons in Pacific Ocean and Cyclones in Indian Ocean.)
*Must have at least 119 km/hr.
*As long as it is over water, gains strength and continues …
– water provides energy for storm
– once it hits land, its source of energy
disappears

18. How Hurricane forms … 1) Low pressure system over ocean.
2) Tropical Depression forms = thunderstorms w/ winds bt. 37 – 62 km/hr.
3) Tropical Storm – air continues to rise … winds > 63 km/hr, thunderstorms
4) Winds > 119 km/hr = hurricane.

19. Parts of Hurricane Eye – center w/ clear skies and light wind. Eyewall
Rainbands
P. 466
Pictures of damage?

20. Blizzards: conditions must be
1. Winds 56 km/h
2. Temp is LOW
3. Visibility is less than 400 m. in falling or blowing snow.
4. Conditions persist for 3 hours or more.
1. Winds 56 km/h
2. Temp is LOW
3. Visibility is less than 400 m. in falling or blowing snow.
4. Conditions persist for 3 hours or more.

21. Severe Weather Safety
WATCHES: issued when conditions are favorable for severe weather like tornadoes, thunderstorms, winter storms …
WARNINGS: severe weather conditions already exist (may be moving into our area)

22. Assign: Sect 2 Questions
P. 468 (1-8)
Next up …
reading Weather Maps

23. Section 3 : Weather Forecasts
Meteorologists:
person who studies the weather.
Takes/uses measurements of temperature, air pressure, winds, humidity, and precipitation to:
Used to make weather maps
The maps allow them to make predictions about future weather patterns.

24. Measuring the Weather 1) Surface Report
Def: describes a set of weather measurements made on Earth’s surface.
Weather Stations – instruments that report:
temp, air pressure, humidity, precip, & wind direction/speed. (weather VARIABLES)

25. Measuring weather cont.
2) Upper-air Report
Def: describes wind, temp, & humidity conditions ABOVE Earth’s surface.
Measured by a RADIOSONDE (carries weather instruments)
Many km high in atmosphere in a weather balloon.
pictures of weather balloon

26. Measuring weather cont.
3) Satellite / Radar Images
Infrared Images
How much thermal energy stored is in atmosphere.
Cloud height
Atmospheric temps
Doppler Radar –
Detects precipitation
Movement of small particles (used to approximate wind speed)
Important tool during severe storms

27. Station Models Data gathered at Earth’s surface
Used to make a map w/ symbols called Station Model
This info entered into computer w/ the data collected from atmosphere - used to make forecasts (what is coming or happening to the weather)

28. How Temperature and Pressure are represented on the maps …
Isobars – line that connects areas of equal atmospheric pressure.
Help indicate where areas of High and Low- pressures are …
Lines closer together means stronger winds …
Isotherms – line that connects areas of equal temperature.

29. Know how to read a Weather Map
P. SR – 46 Weather Map Symbols
P. 473 Weather Map

30. Analyze this station model

31. Wind Speed and direction Previous weather Current weather
Cloud Cover
Temperature
Dew Point
Wind Speed and direction
Previous weather
Current weather
Pressure change
What’s this tell you?

32. End of Chapter 13 Read Chapter if you haven’t.
Make your note cards or foldables.
Study them every night from now until the test.