1. Table of Contents
Air Masses and Fronts
Storms
Predicting the Weather

2. Classifying Air Masses
- Air Masses and Fronts
Classifying Air Masses
Four major types of air masses influence the weather in North America: maritime tropical, continental tropical, maritime polar, and continental polar.

3. Types of Air Masses - Air Masses and Fronts
Air masses can be warm or cold, and humid or dry. As an air mass moves into an area, the weather changes.

4. How a Front Forms - Air Masses and Fronts
The boundary where unlike air masses meet is called a front.

5. Types of Fronts - Air Masses and Fronts
Colliding air masses can form four types of fronts: cold fronts, warm fronts, stationary fronts, and occluded fronts.

6. Weather Fronts Activity
- Air Masses and Fronts
Weather Fronts Activity
Click the Active Art button to open a browser window and access Active Art about weather fronts.

7. Cyclones and Anticyclones
- Air Masses and Fronts
Cyclones and Anticyclones
Winds spiral inward towards the low-pressure center of a cyclone. Winds spiral outward from the high-pressure center of an anticyclone.

8. Comparing and Contrasting
- Air Masses and Fronts
Comparing and Contrasting
As you read, compare and contrast the four types of fronts by completing a table like the one below.
Types of Weather
Front
How It Forms
Cold front
A cold air mass overtakes a warm air mass.
Clouds, possibly storms with heavy precipitation
Warm front
A warm air mass overtakes a cold air mass.
Clouds, light precipitation
Stationary front
Cold and warm air masses meet, but neither can move the other.
Clouds, precipitation
Occluded front
A warm air mass is caught between two cold air masses.
Clouds, precipitation

9. End of Section: Air Masses and Fronts

10. Thunderstorm Formation
- Storms
Thunderstorm Formation
A thunderstorm forms when warm, humid air rises rapidly within a cumulonimbus cloud.

11. Tornado Formation - Storms
Tornadoes can form when warm, humid air rises rapidly in thick cumulonimbus clouds—the same type of clouds that bring thunderstorms.

12. - Storms
Tornado Alley
Tornadoes in the U.S. are most likely to occur in a region known as Tornado Alley.

13. Structure of a Hurricane
- Storms
Structure of a Hurricane
In a hurricane, air moves rapidly around a low-pressure area called the eye.

14. Hurricane Andrew - Storms
The path of Hurricane Andrew over three consecutive days can be seen below.

15. Lake-Effect Snow - Storms
As cold dry air moves across the warmer water, it becomes more humid as water vapor evaporates from the lake surface. When the air reaches land and cools, snow falls.

16. - Storms
Sequencing
As you read, make a flowchart like the one below that shows how a hurricane forms. Write each step of the process in a separate box in the order in which it occurs.
Hurricane Formation
Begins as a low-pressure area over warm water, or a tropical disturbance.
Warm, humid air rises and begins to spiral.
As air rises, more warm, moist air is drawn into the system and the hurricane gains energy.
As winds spiral inward, bands of high winds and heavy rains form.

17. More on Thunder and Lightning
- Storms
More on Thunder and Lightning
Click the Planet Diary button for an activity about thunder and lightning.

18. Click the Video button to watch a movie about tornadoes.
- Storms
Tornadoes
Click the Video button to watch a movie about tornadoes.

19. Click the Video button to watch a movie about hurricanes.
- Storms
Hurricanes
Click the Video button to watch a movie about hurricanes.

20. End of Section: Storms

21. Red Sky - Predicting the Weather
A red sky is one kind of observation that helps people to predict the weather.

22. Computer Weather Forecasting
- Predicting the Weather
Computer Weather Forecasting
Scientists use computers to develop different models of how a front may move. These predictions are then used to make weather forecasts. As more data become available, some models are found to be incorrect, while others are found to closely fit the predicted conditions. The upper graph shows the predicted air pressure from two models. The lower graph shows actual data for air pressure.

23. Computer Weather Forecasting
- Predicting the Weather
Computer Weather Forecasting
Reading Graphs:
What two variables are being graphed?
Time of day and air pressure

24. Computer Weather Forecasting
- Predicting the Weather
Computer Weather Forecasting
Interpreting Data:
How is air pressure predicted to change according to each model in the top graph?
According to model A, air pressure will drop slightly then increase. According to model B, air pressure will steadily decrease.

25. Computer Weather Forecasting
- Predicting the Weather
Computer Weather Forecasting
Inferring:
Which computer model most closely matches the actual air pressure data?
Model B

26. Computer Weather Forecasting
- Predicting the Weather
Computer Weather Forecasting
Predicting:
What weather would you forecast for Monday and Tuesday? Explain.
Stormy weather, clouds, and precipitation accompany low air pressure.

27. Reading Weather Map Symbols
- Predicting the Weather
Reading Weather Map Symbols
The figure below shows what various weather symbols mean.

28. Reading Weather Maps - Predicting the Weather
This is the type of weather map produced by the National Weather Service. It shows data collected from many weather stations.

29. Reading Weather Maps - Predicting the Weather
Weather maps in newspapers use symbols to show fronts, high- and low-pressure areas, and precipitation. Color bands indicate different temperature ranges.

30. Previewing Visuals - Predicting the Weather
Before you read, preview Figure 21, a weather map. Then write four questions that you have about the map in a graphic organizer like the one below. As you read, answer your questions.
Previewing Figure 21
Q. What type of front is located west of Okalahoma City?
A. A cold front
Q. What do the stick symbols indicate?
A. Amount of cloud cover, atmospheric pressure, wind direction and speed, and temperature
Q. What are the slender, curvy lines?
A. Isobars, which join places with the same air pressure
Q. What does the symbol to the east of Florida mean?
A. A hurricane

31. Click the Planet Diary button for an activity about weather maps.
- Predicting the Weather
More on Weather Maps
Click the Planet Diary button for an activity about weather maps.

32. Click the PHSchool.com button for an activity about Doppler radar.
More on Doppler Radar
Click the PHSchool.com button for an activity about Doppler radar.

33. End of Section: Predicting the Weather

34. Graphic Organizer Typical Time of Year Type of Storm Where Forms
Safety Rules
Within large cumulonimbus clouds
Seek shelter, avoid trees and water.
Thunderstorms
Spring or Summer
Move to a storm shelter or basement if possible; stay away from windows and doors.
Tornado
Cumulonimbus cloud
Spring, early summer
Over warm ocean water
Late summer and into autumn
Evacuate or move inside a well-built building.
Hurricane

35. End of Section: Graphic Organizer