1. Severe Weather Events UNIT 10
STANDARDS: NCES 2.5.2, 2.5.3, , 2.6.1, 2.6.2, 2.6.4
LESSON 4

2. Lesson Objectives In this lesson, you will learn about:
Why some thunderstorms are more severe than others
The dangers associated with severe thunderstorms
How tornadoes form
What happened to Greensburg, Kansas

3. Severe Thunderstorms Supercells Lightning Rain Hail Tornado?
When the thunderstorm goes wild. It is like a thunderstorm on steroids. May last for several hours. Winds may exceed 150 mph.

4. Floods Floods are often associated with thunderstorms.
They may also be the result of sustained rain over a long period of time.
Floods result when there is more water than the surface or rivers can handle.
Flooding from Hurricane Floyd in NC 1999

5. Tornadoes or Twisters Minimum Maximum Typical 1 minute 7 hours
Tornadoes are violent, circular whirlpools that hang from the bases of cumulonimbus clouds and extend to the ground. The circular wind MUST touch the ground.
Those not reaching the ground are called “funnel clouds”.
Variable
Minimum
Maximum
Typical
Duration
1 minute
7 hours
10 minutes
Path
Few feet
300 miles
2-5 miles
Width
5 miles
100 yards
Wind Speed
100 mph
280 mph
180 mph

6. Tornado Factors
Duration: The shortest tornado observed spent less than one minute in contact with the ground. On the other hand, the endurance champ was one estimated to have lasted seven hours.
Path Length: The typical swath cut by a tornado is about 2 to 5 miles. Some tornadoes touch down for a short distance, then lift up off the ground for a short distance and then retouch the ground.
Width: The typical width of a tornado is about 100 yards. The widest one observed was associated with the storms that hit Xenia, Ohio, and did damage over an area five miles wide.

7. Fujita Intensity Scale
A scale that measures the destructive power of the tornado.

8. Greensburg, Kansas (GONE!!)
More recent is the Greensburg, Kansas tornado that struck on May 4, 2007 was estimated to be 1.7 miles in width and traveled 22 miles.

9. Tornado Facts for the United States
More people are killed each year by lightening than tornadoes.
Tornadoes can occur at any time of the day or night. The “best” time for them to occur is between 4pm and 7pm.
The destructive forces of a tornado in order of importance:
High winds create a destructive pressure against walls, windows
The devastating effect of missiles propelled by the wind.
The collapse of a structure is a danger.
The explosion caused by the difference between the high pressure inside a structure, and the low pressure within the tornado.
Nowhere on Earth are tornadoes more common than right here in the U.S. It’s estimated that each year about 200 tornadoes touch down, the bulk of them in the Midwest and the High Plains.

10. Tornado Safety
When forecasters for the National Weather Service feel that atmospheric conditions could produce severe weather, they will issue a Tornado Watch.
This means that no tornadoes have been sighted, but conditions are favorable for a tornado to develop.
When a tornado is spotted on radar, or reported by law enforcement officials, or meteorologists, a Tornado Warning will be issued.
This means that a tornado has been sighted.
SEEK SHELTER
When seeking shelter from a tornado, the best place to be is underground; either in a storm cellar or a basement.

11. Section Review 10.4.1 Describe the formation of a supercell.
How do tornados form?
What does the Fujita Scale measure?
Why are tornados dangerous?
What happened to Greensburg, Kansas
Distinguish between a tornado watch and a tornado warning.
What should you do during a tornado warning?