1. Ch. 2 Weather Section 1 What is Weather? Section 2 Weather Patterns
Section 3 Weather Forecasting

2. Section 1 What is Weather?
Refers to the state of the atmosphere at a specific time and place

3. Weather Factors
Describes conditions such as air pressure, wind, temperature, and humidity, or moisture in the air.
The Sun provides almost all of Earth’s energy.
Drives the Water Cycle
Causes wind to occur

4. Temperature Review Temperature is a measure of air molecule movement
High temp. = Warm = air molecules move rapidly
Low temp. = Cold = air molecules move slowly

5. Wind
Movement of air in a specific direction = from regions of higher pressure to regions of lower pressure
Cool air is denser so higher pressure
Warm air is less dense so lower pressure

7. Direction can be determined using a:
Wind Vane - has an arrow that points in the direction from which wind is blowing
Wind Sock - has one open end that catches the wind, causing sock to point in the direction toward which wind is blowing

8. Wind speed can be measured using an:
Anemometer - has rotating cups that spin faster when the wind is strong

9. Humidity The amount of water vapor present in the air
Warm air can hold more water vapor than cool air.
Water vapor condenses and sticks together when cooled
Expressed as g/m3

10. Relative Humidity
A measure of the amount of water vapor present in air compared to the amount needed for saturation at a specific temp.
Expressed as a %

11. Saturation When relative humidity is 100%
Or, in other words, when air is holding the maximum amount of water vapor it can hold at a certain temp.

12. Relative Humidity & Saturation
Air at 25°C is saturated when it contains 22 g of water vapor per cubic meter of air.
The relative humidity is 100 percent.

13. Relative Humidity & Saturation
If air at 25°C contains 11 g of water vapor per cubic meter, the relative humidity is 50 percent.

14. Dew Point The temperature at which air is saturated and dew forms
The dew point changes with the amount of vapor present in the air.
When temperature drops, less water vapor can be present in the air.
The vapor will condense into a liquid or ice crystals

15. Because land cools so quickly, air in contact with the cold ground can reach its dew point, causing dew to form on the ground.
If the temp. is near 0 ˚C, frost will form.
Condensation forms on the outside of a glass because the cold glass brings the air next to it down to its dew pt.

16. Forming Clouds
Clouds form when warm, moist air is forced upward, expands, and cools to its dew point
Water vapor condenses around tiny particles called condensation nuclei.
Water droplets are so small that they stay suspended. Billions of these droplets form a cloud.

17. Ways in which air lifts and cools:
Rays from the Sun heat the ground and the air next to it making it buoyant. The warm air rises and cools.
As moist air moves over mountains, it is forced upward and cools.
When cool air meets warm, moist air along frontal boundaries the warm air rises and cools.

19. Classifying Clouds Classified mainly by shape and height Shapes:
Stratus - form layers, or smooth even sheets in the sky
Fog - stratus clouds that form near the ground
Cumulus - puffy, white clouds, often with flat bases
Cirrus - thin, white feathery clouds made of ice crystals

20. Height: (prefixes) Cirro - high clouds Alto - middle-elevation clouds
Strato - low clouds

21. Rain- or Snow-Producing Clouds
Have the word nimbus or nimbo attached to them
Sunlight usually cannot penetrate through
Ex: cumulonimbus, nimbostratus

22. Precipitation Water falling from clouds 4 main types:
Rain
Snow
Sleet
Hail
Form is determined by air temperature

23. Rain
When the air is warm, water vapor forms raindrops that fall as rain
Size depends on:
Strength of updraft
Stronger = larger drops
Rate of evaporation
If the air is dry, size can be reduced by evaporation before reaching the ground

24. Snow
Forms when the air temp. is so cold that water vapor changes directly to a solid

25. Sleet
Forms when raindrops pass through a layer of freezing air near Earth’s surface

26. Hail
Forms in cumulonimbus clouds when water vapor freezes in layers around a small nucleus of ice
The stronger the updraft, the larger the hailstone
Most hailstones are < 2.5 cm, but some can be as large as a softball
Causes the most damage of all forms of precipitation

27. Question 1
The state of the atmosphere at a specific time and place is __________.
A. climate
B. meteorology
C. season
D. weather

28. Question 2 The amount of water vapor present in the air is __________.
A. dew
B. condensation
C. fog
D. humidity

29. Question 3
What is the dew point?

30. Section 2 Weather Patterns

31. Air Mass
A large body of air that has properties similar to the part of Earth’s surface over which it developed
Can cover thousands of square km
Daily changes in Wx are due to the movement of air masses.

32. 6 air masses of 4 diff. types affect the US:
Maritime Polar (mP) - NW/NE
cool moist
Continental Polar (cP) - N
cold dry
Maritime Tropical (mT) - SW/SE
warm moist
Continental Tropical (cT) - S
hot dry

34. Highs and Lows Air pressure is measured using a barometer.
Remember: Winds blow from high to low pressure areas.

35. Highs Winds blow away from a center of high pressure
Earth’s rotation causes the wind to swirl in a CW dir.
Called anticyclones
Sinking motion in highs makes it difficult for air to rise and clouds to form
High pressure usually signals good Wx.

36. Lows Winds blow toward a center of low pressure
Earth’s rotation causes the wind to swirl in a CCW dir.
Called cyclones
Air rises in a low causing clouds to form.
Lows are usually associated w/ cloudy and/or rainy Wx.

37. Front Boundary b/w two air masses of diff. density, moisture, or temp.
Cloudiness, ppt, and storms sometimes occur at frontal boundaries as air is lifted
4 types:
Cold, Warm, Occluded, Stationary
Need to know symbols!

38. Cold Front Occurs when colder air advances toward warm air
Cold air wedges under warm air like a plow with a steep front causing air to lift and cool rapidly
Generally produces heavy ppt that starts and stops abruptly
Thunderstorms common; tornadoes may form

40. Warm Front
Occurs when lighter, warmer air advances over heavier, colder air
Usually forms a boundary with a gentle slope causing air to lift and cool gradually
Generally produces steady ppt that lasts for hours or days

42. Occluded Front
Occurs when a cold air mass moves toward cool air w/ warm air b/w the two
Colder air forces warm air upward closing it off from the surface

44. Stationary Front Occur when a boundary b/w air masses stops advancing
May remain in place for many days producing light wind and ppt

46. Severe Weather Poses danger to people, structures, or animals
Includes:
Thunderstorms
Tornadoes
Hurricanes
Blizzards

47. Thunderstorms
Form in warm, moist air masses and along fronts whenever air lifts and cools rapidly forming cumulonimbus clouds
Falling raindrops cool the surrounding air. Cool, dense air sinks forming downdrafts.

48. Extremely powerful storms can produce large hailstones. Damage:
Flash flooding
Strong winds (>89 km/h = severe thunderstorm)
Hail
Strong downdrafts
Lightning
Tornadoes

49. Lightning
Occurs when rapid movement of air w/in a storm cloud causes diff. parts of the cloud to become oppositely charged
Lightning is the flow of current b/w regions of op. elec. charge.

50. Can occur w/in a cloud, b/w clouds, or b/w a cloud and the ground
Can reach temp. of about 30,000 ˚C

51. Thunder
Results from the rapid heating of air around a bolt of lightning
The extreme heating of air around lightning causes it to expand and contract rapidly, which forms sound waves heard as thunder

52. Tornadoes Violently rotating columns of air in contact with the ground
Form at the base of cumulonimbus clouds
Ranked according to the Fujita scale according to how much damage they cause (F0 - F5)

53. Hurricanes
Large, swirling low-pressure systems that form over the warm Atlantic Ocean
Called typhoons in the Pacific Ocean and cyclones in the Indian Ocean
Must have wind speeds >199 km/h

54. Ranked according to the Saffir-Simpson scale according to wind speed (Category 1 - Category 5)
Damage:
High winds
Tornadoes
High waves
Storm surges
Floods

55. Blizzards
Winter storms that have winds ≥56 km/h, low temps., and visibility <400 m that persist for at least 3 hours

56. Watches vs. Warnings
Watches - are issued when conditions are favorable for severe Wx
Warnings - are issued when severe Wx conditions already exist

57. Question 1 Water falling from clouds is _______________.
A. Cloud cover
B. Dew
C. Fog
D. Precipitation

58. Question 2
A large body of air that has properties similar to the area over which it develops is ______________.
An air mass
Cloud cover
Fog
Front

59. Question 3
What is the boundary between two air masses of different density, moisture, or temperature called?
How do you classify them?

60. Section 3
Weather Forecasting

61. Meteorologist A person who studies the Wx
Gathers info. about current Wx conditions using tools such as Wx balloons, Wx satellites, Doppler radar, etc. to make predictions about future Wx patterns

62. Collects data from 2 places:
Earth’s surface
Upper atmosphere
Makes Wx maps which are used to help predict the Wx
Uses computers to help predict the Wx

63. Weather Map
Map that shows current conditions and is used to help predict the Wx
Includes station models, highs and lows, fronts, and isobars

65. Station Models Highs and Lows
Show Wx conditions at a specific location on Earth’s surface
Can include info. on up to 20 diff. Wx conditions
Highs and Lows
Drawn as circles with the word “high” or “low” in the middle

67. Fronts Isobars Drawn as lines and symbols
Lines drawn to connect points of equal pressure
Closely spaced isobars indicate a large pressure diff. over a small area, which means high winds

68. Isotherms
Lines drawn to connect points of equal temp.

69. Question 1
A _____________ shows the weather conditions of a specific location on Earth’s Surface.
Isobar
Isotherm
Station Model
Weather map

70. Question 2
On a weather map, the line that connects points of equal temperature is called?
Berm
Isobar
Isotherm
Station Model

71. Question 3
What is an Isobar?