1. Weather Review Day!

2. Air Mass
Air Mass is a large body of air where temperature and moisture content are similar throughout.
Moisture content and temperature are determined by the area over which the air mass is formed called source regions.

3. Air Mass Air Mass is designated by a two- letter symbol.
The first letter indicates moisture content.
The second letter represents temperature.
See chart

4. Cold Air Mass
There are three polar air masses that influence the weather in the United States.
Continental polar, Maritime polar over the North Pacific Ocean, Maritime polar over the North Atlantic ocean

5. Warm Air Masses
There are three warm air masses that influence the weather in the United States.
Maritime tropical that develops over the Gulf of Mexico, Maritime tropical that develops over the Pacific Ocean, Continental tropical

6. Fronts
Fronts are the boundary between air masses of different densities and usually different temperatures.
The four types of fronts are cold front, warm front, occluded front, stationary front.

7. Cold Front
Forms where cold air moves under warm air, which is less dense, and pushes the warm air up.
Cooler weather follows cold fronts.
Cold fronts bring thunderstorms, heavy rain or snow.

8. Warm Front Forms where warm air moves over cold, denser air.
Warm fronts bring drizzly rain and are followed by clear warm weather.

9. Occluded Front
Forms when a warm air mass is caught between two cooler air masses.
Occluded front has cool temperatures and large amounts of rain and snow.

10. Stationary Front Forms when a cold air mass meets a warm air mass.
A stationary front often brings many days of cloudy, wet weather.

11. Air Pressure and Weather
Cyclones and Anticyclones

12. Air Pressure and Weather
Cyclones
An area in the atmosphere that has lower pressure than the surrounding areas.
Air masses converge or move together; winds spiral toward the center

13. Air Pressure and Weather
Anticyclones
Areas where air diverges or moves apart and sinks. Sinking air is denser than surrounding air.
Rotates in a direction opposite to Earth’s rotation.

14. Air Pressure and Weather
Cyclones form clouds and rain when the rising air cools.
Cyclones cause stormy weather.
Anticyclones cause dry, clear weather because as the air sinks it gets warmer and absorbs moisture.

15. Severe Weather

16. Thunderstorms
Thunderstorms are a usually brief, heavy storm that consists of rain, strong winds, lightning, and thunder.
Thunderstorms can occur along cold fronts, but only require warm and moist air near Earth’s surface and an unstable atmosphere.

17. Thunderstorms
An unstable atmosphere occurs when the surrounding air is colder than the rising air mass.
When the rising air reaches its dew point, the water vapor in the air condenses to form dark cumulonimbus clouds.

18. Lightning
Lightning is an electric discharge that takes place between two oppositely charged surfaces, such as between a cloud and the ground, between two clouds, or between two parts of the same cloud.

19. Thunder
Thunder is the sound caused by the rapid expansion of air along an electrical strike.
Balloon Demonstration

20. Severe Thunderstorms
Severe thunderstorms can produce one or more of the following conditions: high winds, hail, flash floods, and tornadoes.

21. Tornadoes
A destructive, rotating column of air that has very high wind speeds , is visible as a funnel-shaped cloud, and touches the ground.
1% of all thunderstorms have a tornado.
The average tornado has wind speeds between 120 and 180 km/h

22. Hurricanes
A severe storm that develops over tropical oceans and whose strong winds of more than 120 km/h spiral in toward the intensely low-pressure storm center.
At the center of the hurricane is the eye, which is a core of warm, relatively calm air with low pressure and light winds.
Hurricanes can vary in size from 160 to 1,500km and can travel thousands of kilometers.

23. Hurricanes
Hurricanes get their energy from the condensation of water vapor.
Moisture is added to the air through evaporation from warm water which eventually condenses and gives the hurricane more energy.

24. Severe Weather Safety Tornado Flood Hurricane Thunderstorm Safety
Watch- an alert that a tornado may happen
Warning- a tornado has been spotted
Go to a basement/cellar or a windowless room in the center of the building; outside lay in a deep ditch
Flood
Find a high place to wait out the flood; stay out of floodwaters
Hurricane
Have a disaster supply kit, evacuate if necessary, cover windows with plywood
Thunderstorm Safety
Stay away from water
If you are outside stay away from trees and crouch down

25. Weather
Water in the Air

26. Weather vs. Climate
Weather is the condition of the atmosphere at a certain time and place.
Weather is hard to predict.

27. So what is climate?
Climate is the weather conditions prevailing in an area in general or over a long period.

28. Storms and Air masses
Storms – disturbances with strong winds and precipitation.
Air masses – large volumes of air with distinct properties.

30. Fronts – boundaries between air masses
Warm front
Cold front
Occluded Front
Stationary Front
Storms typically develop at fronts.
Global winds may cause unusual weather by steering air masses.

31. Water Vapor Water Vapor is the amount of moisture in the air.
The warmer the air, the more water vapor it can hold.
The cooler the air, the less water vapor it can hold.

32. Humidity and Relative Humidity
Humidity is the amount of water vapor in the air.
Relative humidity is the amount of water vapor in the air compared with the maximum amount of water vapor that the air has the potential to hold at a certain temperature.

33. Relative Humidity Saturated air has a relative humidity of 100%
The more water vapor in the air, the higher the relative humidity.
Humidity is measured using a psychrometer or hygrometer and a special table.
Paper towel demonstration

34. Humidity
The two factors that affect relative humidity are the amount of water and temperature.
Clouds can form when there are millions of condensed water droplets in the air.
The water cycle is the natural process that supplies the air with water through evaporation.

35. Dew Point
The dew point is the temperature at which a gas condenses into a liquid.
Condensation cannot occur until the dew point is reached.

37. Rain
A cloud produces precipitation when the water drops in the cloud become large enough to fall.
Rain is the most common form of precipitation.

38. There are four main types of precipitation: rain, snow, sleet, and hail.

39. Sleet forms when rain falls through a layer of freezing air creating falling ice.
Snow forms when temperatures are so cold that water vapor changes directly to a solid.
Snow can fall as a single crystal or join to create snowflakes.
Sleet and Snow

40. Hail
When updrafts of air in the clouds carry raindrops high in the clouds, the raindrops freeze and hail forms.

41. WEATHER FORCASTING!

42. Weather Maps

43. Scientists and weather forecasters use weather maps to help them see weather patterns.

44. They place symbols on the maps to help them see what is going on with the weather in various parts of the country.

45. A Cold Front symbol shows the edge of a mass of cool air.

46. A Warm Front symbol shows the edge of a warmer air mass.

47. A Stationary Front means neither the warm air or the cool air are moving very much.

48. How many fronts can you identify on this map?

49. Higher pressure usually means nice, clear weather.
A large “H” means an area of higher pressure. H
Higher pressure usually means nice, clear weather.

50. Which state has high pressure?

51. L A large “L” means an area of lower pressure.
Lower pressure usually means clouds, rain, or snow.

52. How many “Lows” are on this map?

55. Occluded Front

56. Stationary Front

57. Warm Front

58. Cold Front

62. Cloud Types

63. What are clouds?
A cloud is made up of tiny water droplets and/or ice crystals.

64. How do clouds form? Clouds form as warm air rises and cools.
The air cools and becomes saturated so the water vapor changes from a gas to a liquid.

65. Don’t believe me?
Listen to this dude:

66. Cloud Types
Clouds are classified by their form and altitude.

67. Clouds There are 3 main types of clouds: Cumulus or fluffy clouds
Stratus or layered clouds
Cirrus or thin feathery clouds
Cumulus
Stratus
Cirrus

68. Cirro – High Clouds
Alto – Middle Clouds
Strato – Lower Level
Nimbo – Rain, Precipitation
Cumulo – Heap

69. Cirrus

70. Cirrus
Cirrus clouds are thin, feathery, white clouds found at higher altitudes.

71. Cirrus
Forms when the wind is strong.

75. Cirrus Clouds
Cirrus generally occur in fair weather and point in the direction of air movement at their elevation.

76. Cirrus Clouds

77. Stratus Clouds
Stratus Clouds stretch across the sky in low, large flat layers. They resemble fog, but they do not reach the ground. They often produce mist or drizzle.

78. Stratus Clouds
Form in layers.
Cover large areas of the sky and often block the sun.

79. How are Stratus clouds formed?
Caused by a gentle lifting of a large body of air into the atmosphere.

80. Fog is a stratus cloud that has formed near the ground

81. Stratus
The word stratus comes from the Latin word that means "to spread out." Stratus clouds are horizontal, layered clouds that stretch out across the sky like a blanket.

82. Stratus Clouds

83. Stratus Clouds

87. Vertically Developed Cumulus Clouds
Fair weather cumulus have the appearance of floating cotton and have a lifetime of 5-40 minutes. The word cumulus comes from the Latin word for a heap or a pile. Cumulus clouds are puffy in appearance. They look like large cotton balls.

88. Cumulus Clouds Puffy, white clouds that tend to have flat bottoms.
Form when warm air rises.
Generally indicate fair weather, but when they get larger they produce thunderstorms.

89. Cumulus
The clouds that produce heavy thunderstorms in summer are a form of cumulus clouds called cumulonimbus.

90. Fair Weather Cumulus

94. Cumulonimbus Clouds
The type of cumulus cloud that produce thunderstorms.
Clouds that have names that include –nimbus or nimbo – are likely to produce precipitation.

95. Cumulonimbus Clouds

96. Nimbostratus Clouds
Dark stratus clouds that usually produce light to heavy continuous rain.

97. Altitudes of Clouds
Clouds can also be classified by the altitude at which they form.
The prefix “cirro” is used to describe clouds that form at high altitudes.
The prefix “alto” is used to describe clouds that form at middle altitudes.

98. Let’s take a second look
Shall we?

99. Cirro – High Clouds
Alto – Middle Clouds
Strato – Lower Level
Nimbo – Rain, Precipitation
Cumulo – Heap