1. Severe Weather

2. Thunderstorms
Small intense systems that can produce strong winds, rain, lightning and thunder.
Need 2 conditions
Air near surface needs to be warm and moist
The atmosphere must be unstable

3. Becoming unstable…
The surrounding air is colder than the rising air mass
This makes that rising air CONTINUE rising
The thunderstorm occurs when the air is rising rapidly
Forms cumulonimbus cloud

4. Lightning!
Electrical charges build up near the tops and bottoms of clouds heading from positive to negative to positive (opposites attract)
Flash of light occurs when a charge sparks
The flash heats the air to about the temperature of the surface of the sun
ENERGY IS RELEASED

5. More… Thunderstorms get their energy from humid air
Can produce high winds, flood, or tornadoes

6. Effects Thunderstorms can have positive or negative effects
Positive – rain can provide water for crops and restore lakes and streams
Negative
Flash floods
Winds
Hail
Lightning

7. Funnel Cloud
Wind traveling in 2 different directions causes it to start spinning
The updrafts of air push the spinning column down, sometimes to the ground
It is called a tornado once it hits the ground
Funnel cloud Tornado

8. Tornadoes Cumulonimbus clouds can sometimes form tornadoes
Only 1 percent of thunderstorms form tornadoes

9. Formation About 75 percent of tornadoes happen in the United States.
Warm humid air comes up from the Gulf of Mexico and meets cold dry air from Canada in the plains.

11. Path
A tornado moves along with its thunderstorm, it travels fast and weaves a path that is impossible to predict
Tornado watch
When the weather conditions might produce tornadoes.
Tornado warning
When a tornado has
been detected

12. Hurricanes Most powerful storms on Earth Different names
Typhoons – Pacific Ocean
Cyclones – Indian Ocean
Form over warm tropical oceans
Vary in size and can travel
thousands of miles

14. Formation of Hurricanes
Hurricane Season – August to October
Begins as a group of thunderstorms
Energy
Comes from condensed water vapor
Fuel
Direct contact with warm ocean water
Hurricanes will continue to grow until they lose their source of warm, moist air

15. Hurricane Features

16. Effects of Hurricanes Wind Speed
120 km/h to 300 km/h
When a hurricane moves into a coastal area it causes a storm surge (raise sea level) and flooding

18. Winter storms produce snow and ice
Winter storms are formed when two air masses collide. A continental polar air mass forming over snow is especially cold, dry, and dense. It forces moist air to rise very quickly.

19. Blizzards
A storm with falling or blowing snow, winds at least 35 mph, reduced visibility and intense cold.
Occur in many parts of the Northern and Central United States.

20. Formation of a Blizzard
Very similar to thunderstorms, only the air is rising even higher.
Warm air has the moisture, and is pushed even higher than normal, passing through clouds that are high in the sky
Those clouds take some moisture, and it freezes

21. Duration of a Blizzard
For a storm to be considered a blizzard it has to last at least 3 hours.
Some blizzards can last for a few hours or even days!

22. Dust Storm
Strong, violent winds that carry fine particles like silt, clay, sand and dust-filled air over an extensive area.

23. Formation of a Dust Storm
Any area with a lot of dust and sand particles
Need dry air and a lot of wind
Huge
Can spread over hundreds of miles
Powerful
Wind speeds of at least 25 miles per hour (40 km)

24. Dangers of a Dust Storm Arrive without warning
Create large wall of dust and debris.
Last only a few minutes
Leave debris behind
Hard to see during storm
Breathing is impacted.
Takes fertile top soil away and reduces future crops.
Current crops are covered with dust.