1. Bell Ringer
Cumulonimbus clouds have a tall structure and a flat base. What are they usually associated with?

2. Thunderstorms and Tornadoes
Severe Storms
Thunderstorms and Tornadoes

3. What do you know about Thunderstorms?

4. Have you ever seen a small whirlwind carry dust or leaves upward on a hot day?

5. Thunderstorms A storm that generates lightning and thunder.
Frequently produce gusty winds, heavy rain, and hail.
Associated with cumulonimbus clouds

6. Lightning: results from the build up and discharge of electric energy between positively (ground) and negatively (clouds) charged area
Thunder: the sound of rapidly expanding gases usually associated with lightning

7. Warm Up
What causes lightning?
What causes thunder?
True or False: Lighting can strike 10 miles away from the storm cloud.
What causes clouds to form?
What type of pressure is found in the center of a storm?

8. Warm Up What causes lightning?
A build up of negative charges in the clouds discharges to the positively charged surface
What causes thunder?
When lightning strikes, it super heats the air and the instant heating causes the air to expand suddenly.
True or False: Lighting can strike 10 miles away from the storm cloud.
True
What causes clouds to form?
Rising air pulls water moisture into the atmosphere. As the moisture cool, it condenses into clouds
What type of pressure is found in the center of a storm?
Low

9. How common are thunderstorms?

10. Occurrence of Thunderstorms
Estimated 2000 in progress on Earth at any time
About 45,000 take place each day
More than 16 million occur annually around the world

13. The greatest number occur in the tropics
Atmospheric Conditions needed:
Warm, moist air, uplift, and instability

14. Development of Thunderstorms
Form when warm, humid air rises in an unstable environment
3 Stages
Cumulus Stage
Mature Stage
Dissipating Stage

15. Cumulus Stage
Warm, moist air is supplied to the cloud by strong updrafts
Cloud grows vertically

16. Mature Stage Begins within 1 hour of the initial updraft
Most active stage
Heavy precipitation, gusty winds, lightning, and sometimes hail are produced

17. Dissipating Stage Cloud begins to evaporate
The cooling effect of the falling precipitation and the flowing in of colder air from high above causes the storm to die down

18. Thunderstorm Development
The Thunderstorm Recipe Video

19. What do you know about tornadoes?

20. Tornadoes
Violent low pressure windstorms that take the form of a vortex.
Vortex- spinning/rotating, often turbulent, column of air
The vortex extends downward from a cumulonimbus cloud – produce rain and hail
Move counterclockwise

21. Occurrence of Tornadoes
About 770 tornadoes are reported in the United States each year
Frequency is greatest between April and June
Associated with Severe Thunderstorms

22. Which states in the U. S. do you think get the most tornado touchdowns?

23. Development of Tornadoes
Most form in association with severe thunderstorms
The formation of the mesocyclone is an important process in tornado formation.
National Geographic Tornadoes Video

24. Mesocyclone
A vertical cylinder of rotating air that develops in the updraft of a thunderstorm

25. Formation of a Mesocyclone
How Tornadoes Form Video

26. Tornado Intensity
Pressure within tornadoes can be as much as 10% lower than the pressure outside the storm.
Intensity is measured on the Fujita Scale

27. Fujita Scale First introduced in 1971 – Tetsuya Fujita
Measures the strength of tornadoes
Based on storm damage
Ranges from F0-F5
Updated 2007 – Enhanced Fujita
Updated wind speeds match damaged caused by tornado

28. Fujita Tornado Intensity Scale
Enhanced Fujita Scale

29. Fujita Tornado Scale Category Winds (MPH) Winds (KPH) Damage F0 <73
<116
Light damage F1
73-112
Moderate Damage F2
Considerable Damage F3
Severe Damage F4
Devastating Damage F5
>260
>419
Incredible and Speechless Damage

30. Watch vs. Warning

31. Tornado Watch
Alert people to the possibility of tornadoes in a specified area for a particular time
Conditions are right for a tornado to happen

32. Tornado Warning
Issued when a tornado has actually been sighted in an area or;
Indicated by weather radar

33. Exit Ticket Severe Storms Causes Effects Thunderstorms a) b) Tornadoes