1. Chapter 13
The Nature of Storms

2. Lesson 1
Thunderstorms

3. Think About It…
During which months do we get the most damaging thunderstorms here in the Piedmont?

4. How do the major types of thunderstorms form?
Focus Question…
How do the major types of thunderstorms form?

5. Average Number of Thunderstorm Days Annually…

6. Types of Thunderstorms…
Air Mass - Mountain
Where… within one air mass over a mountain
Why… warm air rises over a mountain, forming storm clouds!
When… midafternoon

7. Types of Thunderstorms…
Air Mass - Sea-Breeze
Where… coastal areas, esp. tropics/subtropics
Why… temperature differences between land and sea create convection cells and updrafts
When… summer

8. Types of Thunderstorms…
Types of Thunderstorms…
Frontal - Cold
Where… at the leading edge of a cold front
Why… cold air pushes warm air rapidly up at the steep cold-front boundary
When… anytime a cold front moves in!

9. Types of Thunderstorms…
Frontal – Warm
Where… at the leading edge of a warm front
Why… warm air mass slides up over a cold air mass creating clouds
When… if a warm front moves in with enough moisture and instability

10. Thunderstorms in the Piedmont…
Which types of thunderstorms do we experience here in the Piedmont?
Frontal (warm and cold)
Local Air Mass (in the summer)

11. Stages of Development of a Thunderstorm…

12. NSSL – Q&A Thunderstorms…
The National Severe Storm Laboratory is in Norman, OK.

13. Severe Thunderstorms anvil Rain Free Base Precipitation

14. How Lightning Forms …

15. Lightning… A giant spark of static electricity
What is lightning?
A giant spark of static electricity
When does a lightning bolt form?
When there is an electrical imbalance between clouds (-) and the ground (+)
What is a stepped leader?
An invisible channel of negatively charged air from a cloud

16. Lightning… 4. What is return stroke (positive streamer)?
A channel of positively-charged ions from the ground
5. How hot is lightning?
30,000 degrees Celsius
6. What causes thunder?
Super-heated air expanding and contracting

17. Lightning Damage… 7500 forest fires/year 300 injuries/ 93 deaths/year
Lightning Damage…
Describe the damage that lightning can do.
7500 forest fires/year
300 injuries/ 93 deaths/year
Property damage
Lightning-struck trees on the Blue Ridge Parkway

18. Lightning Q&A and Safety…

19. Lesson 2
Severe Weather

20. Where is the safest place to be during a tornado?
Think About It…
Where is the safest place to be during a tornado?

21. How do tornados form and how are they classified?
Focus Question…
How do tornados form and how are they classified?

22. The Fury of the Wind… 1. What is a downburst?
A violent downdraft concentrated in a local area
2. What are the two types of downbursts?
macro- (big) and micro- (small)
3. Microbursts are deadly because they are harder to detect and prepare for.

23. Floods… 4. What are 3 conditions that cause floods to occur?
Abundant moisture over a limited area.
Rain falls faster than the ground can absorb it.
Wind currents in the upper atmosphere are weak so that weather systems move slowly

24. The Flooding Mississippi River
Slide show May 17, 2011…

25. Tornados…
A change in wind direction and speed creates a horizontal rotation.
Strong updrafts tilt the rotating air to a vertical position.
A tornado forms within the rotating winds.

26. Tornado Alley - The Midwest!
A cP air mass from Canada meets a mT air mass from the Gulf of Mexico forming a supercell.
A supercell is a giant, self-sustaining storm that can spawn tornados.

27. The Enhanced Fujita Scale…EF0 or EF1
- % of all tornados… 80
- Path…
up to 3 miles
- Wind Speed…
mph
- Duration…
1 – 10 minutes
Dr. Theodore Fujita

28. The Enhanced Fujita Scale…EF2 or EF3
- % of all tornados… 19
- Path…
15+ miles
- Wind Speed…
mph
- Duration…
20+ minutes

29. The Enhanced Fujita Scale…EF4 or EF5
- % of all tornados…
1 (Thankfully!)
- Path…
50+ miles
Wind Speed…
200+ mph
Duration…
1+ hours

30. Tornado Safety…
Move to a pre-designated shelter – to a basement if possible.
Move to an interior room/hall, lowest floor, under sturdy furniture.
Stay away from windows.
Get out of vehicles!
Don’t try to outrun a tornado.
If outside, lie flat in a ditch or depression.
Abandon a mobile home for a shelter.

31. Lesson 3
Tropical Storms

32. From which direction do the hurricanes which hit our east coast come?
Think About It…
From which direction do the hurricanes which hit our east coast come?

33. How does a hurricane form?
Focus Question…
How does a hurricane form?

34. Tropical Cyclones… Large, rotating, low pressure storm hurricanes
A tropical cyclone can be described as a…
Large, rotating, low pressure storm
We call these storms…
hurricanes
3. Tropical cyclones derive a tremendous amount of energy from…
Warm, tropical oceans

35. Fran, 1996, Cape Fear, NC Name was retired!
Tropical Cyclones…
Which direction do tropical cyclones turn in the northern hemisphere?
Counterclockwise
It is a low pressure system!
Fran, 1996, Cape Fear, NC Name was retired!

36. Tropical Cyclones…
As a hurricane strengthens, what do the following components do?
Air pressure in eyewall– decreases
Surface wind speeds – increase
What are two basic conditions that tropical cyclones require to form?
Lots of warm ocean water
Disturbance to lift the air

37. Tropical Cyclones… the west! the prevailing westerlies
Tropical cyclones move steadily towards…
the west!
Which wind system moves across the USA and usually guides hurricanes out into the Atlantic Ocean?
the prevailing westerlies
Hurricane Rita – 2005, 3rd lowest pressure in Atlantic (897 mb), hit as cat. 3

38. Development of a Tropical Cyclone…
Tropical Disturbance – a weak, low-pressure system – group of thunderstorms collect

39. Development of a Tropical Cyclone…
Development of a Tropical Cyclone…
Tropical Depression – a disturbance begins to rotate around the center of low pressure
Katrina as a tropical depression

40. Development of a Tropical Cyclone…
Development of a Tropical Cyclone…
Tropical Storm – a depression is labeled a storm when the wind speeds reach 39 mph.
Tropical Storm Dalila, July 2007

41. Development of a Tropical Cyclone…
Development of a Tropical Cyclone…
Tropical Hurricane – pressure drops and the wind speeds reach 74 mph
Dean 2007
Katrina 2005
Ivan2006

42. Hurricane History…

43. Anatomy of a Hurricane…

44. Classifying Hurricanes…
What scale is used to classify hurricanes?
Saffir-Simpson
What are the three characteristics of a hurricane described by the scale?
Wind speed – how high?
Air pressure – how low?
Potential for damage – how much?!

45. Classifying Hurricanes…
The Saffir-Simpson Scale…
Categories 1 – 5
For a tropical storm to be considered a cat. 1 hurricane – 74 mph
The category that does the most damage – 5
Wind speed of a cat 5? > 155 mph
Three most powerful storms to hit USA?
Florida Keys, 1935
Camille, 1969
Andrew, 1992

46. Classifying Hurricanes…
A hurricane runs out of energy
When it moves over land
When it moves over cold water

47. Hurricane Hazards… The strongest winds in a hurricane are in …
The eye wall

48. Hurricane Hazards… What is a storm surge?
When hurricane force winds drive a mound of ocean water towards coastal areas

49. Flooding from Hurricane Fran
Hurricane Hazards…
What hurricane hazard is caused by great amounts of rain?
floods
Flooding from Hurricane Fran

50. Hurricane Hazards…
Which agency is responsible for tracking and forecasting hurricanes?
The National Hurricane Center in Miami, FL at the FIU Campus (NOAA)

51. Recurring Weather – Review handout!
Lesson 4
Recurring Weather – Review handout!