1. Science ~ chapter 8 weather
Miss Nelson

2. Section 4
Storms

3. Anticipatory set
What are the four types of fronts? What happens when air masses with different pressure and humidity meet?

4. standards
S 6.4.e – Students know differences in pressure, heat, air movement, and humidity result in change in weather

5. What are the main kinds of storms, and how do they form?
The big idea
What are the main kinds of storms, and how do they form?

6. Key terms Storm – a violent disturbance in the atmosphere
Thunderstorm – a small storm with heavy precipitation and frequent thunder and lightning
Lightning – a sudden spark, or energy discharge, caused when electrical charges jump between parts of a cloud, between nearby clouds, or between a cloud and the ground

7. Key terms
Tornado – a rapidly whirling, funnel-shaped cloud that reaches down to touch Earth’s surface
Hurricane – a tropical storm that has winds of about 119 kilometers per hour or higher
Storm surge – a “dome” of water that sweeps across the coast where a hurricane lands

8. Storms involve sudden changes in air pressure
In turn cause rapid air movements
Conditions that bring one kind of storm often cause other kinds of storms in the same area
Conditions that cause thunderstorms can also cause tornados

9. How thunderstorms form
Thunderstorms form in large cumulonimbus clouds
Also known as thunderheads

10. How thunderstorms form
Most cumulonimbus clouds form on hot, humid afternoons
Also form when warm air is forced upward along a cold front
Many thunderstorms form in the spring and summer in southern states or on the Western Plains

11. Lightning and thunder
During a thunderstorm areas of positive and negative electric charges build up in the storm clouds
Lightning is a sudden spark, or electric discharge, as these charges jump between parts of a cloud
Similar to the shocks you sometimes feel when you touch a metal object on a dry day… but on a MUCH larger scale!

12. Lightning and thunder
A lightning bolt can heat the air near it to as much as 30,000 degrees Celsius
MUCH hotter than the sun’s surface
The rapidly heated air expands suddenly and explosively
Thunder is the sound of the explosion
Because light travels faster than sound, you see lightning before you hear thunder

13. Thunderstorm damage Can cause severe damage
The heavy rains associated with thunderstorms can flood low-lying areas
Lightning strikes can shatter tree trunks or start forest fires
When lightning strikes a person it is like a powerful electric shock
Can cause burns, unconsciousness, or even heart failure

14. floods
A major danger during thunderstorms is flooding

15. Thunderstorm safety
During thunderstorms, avoid places where lightning may strike Also avoid objects that can conduct electricity, such as metal objects and bodies of water

16. Read Thunderstorms on pages 319-320 of your textbook

17. tornadoes One of the most frightening and destructive storms
A rapidly whirling, funnel-shaped cloud that reaches down from a storm cloud to touch Earth’s surface
If it occurs over a lake or ocean it is known as a water spout
Are usually brief
May touch the ground for 15 minutes or less
Only a few hundred meters across
Wind speeds may approach 500 kilometers per hour

18. Tornados most commonly develop in think cumulonimbus clouds
How tornados form
Tornados most commonly develop in think cumulonimbus clouds
The same clouds that bring thunderstorms

19. Are most likely to occur
How tornados form
Are most likely to occur
in spring and early summer
in late afternoon when the ground is warm
The Great Plains have the kind of weather pattern that is likely to create tornados
Warm, humid air mass moves north from the Gulf of Mexico into the lower Great Plains
A cold, dry air mass moves south from Canada

20. Tornado alley
Tornados are rare in California
About 800 occur in the United States every year
View figure 21 on page 321 of your textbook

21. Read Tornadoes on pages 320-321 of your textbook

22. snowstorms
All year round, most precipitation begins in clouds as snow If the air is colder than 0°C all the way to the ground, the precipitation falls as snow

23. snowstorms
In California, snowstorms generally occur only at high elevations
Californians depend on snow to provide part of their fresh water needs
Snow that accumulates during the winter melts in the spring and summer
This snowmelt provides fresh water for a variety of needs, including irrigation and electricity production

24. hurricanes
A hurricane is a cyclone that has winds of 119 kilometers per hour or higher
Form in the Atlantic, Pacific, and Indian oceans
In the western Pacific Ocean, hurricanes are called typhoons

25. How hurricanes form
A hurricane begins over warm ocean water as a low-pressure area, or tropical disturbance

26. How hurricanes form
A hurricane draws its energy from the warm, humid air at the ocean’s surface
As the air rises from the clouds, more air is drawn into the system
The lower the air pressure at the center of the storm, the faster the winds blow toward the center

27. How hurricanes form
Hurricane winds are strongest in the narrow band around the center of the storm
At the center is a ring of clouds, called the eyewall, that enclose the quiet “eye”

28. How hurricanes move Hurricanes last longer than other storms
Usually a week or more
During this time they can travel quite far
Hurricanes that form in the Atlantic are steered by the trade winds toward the Caribbean islands and the southeastern United States
After a hurricane passes over land, it no longer has warm, moist air to draw energy from, and gradually loses strength

29. Read Hurricanes on pages 324-325 of your textbook

30. Check for understanding
What weather conditions are most likely to produce tornadoes? Why do tornadoes occur most often in “tornado alley?”

31. Check for understanding
What weather conditions are most likely to produce tornadoes? Think cumulonimbus clouds along a front are the conditions most likely to produce tornadoes. Why do tornadoes occur most often in “tornado alley?” The area known as “tornado alley” often has cold dry air meeting warm, moist air.

32. What is a hurricane? How do hurricanes form?
Guided practice
What is a hurricane? How do hurricanes form?

33. Guided practice
What is a hurricane? A hurricane is a tropical cyclone with very high winds. How do hurricanes form? Hurricanes form when low pressure systems form over warm water. The rising warm, moist air adds energy to the system, which eventually becomes a hurricane.

34. Complete Weather 8-4 Independent Practice