1. Thunderstorms, Tornadoes, and Hurricanes
C.C. Hennon, UNC Asheville
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2. Where are Thunderstorms common?
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Average number of days (per year) that a thunderstorm occurs (Fig 10.18)
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3. Thunderstorms Common in the summer season
Usually not part of a larger-scale weather system
Short-lived, rarely severe
Occur when a warm front and a cold front meet.
Thunderstorms
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ATMS 103

4. Mature Stage Cumulus Stage Dissipating Stage
Lightning, Thunder, Peak strength
Clouds may reach 45-50,000 ft
Cumulus Stage
Updrafts dominate
Precipitation begins to fall
Dissipating Stage
Downdrafts dominate
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5. Stages of an Air Mass Thunderstorm
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6. Severe Thunderstorms
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7. A thunderstorm is a storm with thunder, lightning, and often heavy rain and strong winds.
anatomy of a thunderstorm
What is a Thunderstorm?
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8. Structure of Severe Thunderstorms
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9. Features of Severe Thunderstorms
Cumulus clouds build up to form cumulonimbus clouds.
Heavy rain or hail forms.
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10. Features of Severe Thunderstorms
Downburst
A highly localized, very strong downdraft
Hits ground and spreads out in a circular direction underground/video/inside-a- microburstMicroburst
A downburst with winds only extending less than 4 km in any direction
Winds can be as high as 150 kt.
Extremely hazardous to Aircraft
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ATMS 103

11. Enhanced lift ends, plane pushed downward
Strong headwind/lift
Enhanced lift ends, plane pushed downward
Strong tailwind stalls plane, crash ensues
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12. Microburst produced increased lift initially
Plane then experienced dramatic tailwind and decrease in lift
Crash killed 136 / 167
Delta 191 Crash At DFW, 1985
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13. Supercell Thunderstorm
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14. Thunderstorms
Line of storms that form just ahead of a cold front or some distance ahead ( km)
Can be over 600 miles long
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15. Lightning and Thunder
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16. Thunder – Shock wave produced by lightning
Lightning - An electrical discharge formed by charge separation within thunderstorms or between thunderstorms and the ground
Thunder – Shock wave produced by lightning
Lightning heats air to around 30,000 K
Air expands very rapidly, creates loud noise
Hurricane Matthew lightning
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ATMS 103

17. Lightning Characteristics
Globally, about 100 flashes occur each second
Most lightning (~80%) occurs between clouds. Only about 20% is between cloud and ground
About 100 deaths/year in U.S. by lightning strikes (second most by a natural phenomena)
Most in Florida
Hazardous activities: golf, sailing, walking in open area
Lightning Characteristics
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18. Travels about 1100 ft./sec
If lightning flash is 3 miles away, it will take about 9 seconds for thunder to be heard
If lightning hits you, you will instantaneously hear thunder before vaporizing
Thunder
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19. C.C. Hennon, UNC Asheville
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20. Net negative charge builds up near bottom of cloud
This attracts net positive charge buildup from ground
When charge separation is too great, lightning strike will occur
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ATMS 103

21. C.C. Hennon, UNC Asheville
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22. Types of Lightning Cloud to cloud Cloud to ground Ball lightning
Appears as a luminous sphere
Cause unknown
Sheet lightning
Lightning inside of clouds, appears white
Types of Lightning
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23. wvlightning.com/types.shtml
Ribbon Lightning
Bead Lightning
St. Elmo’s Fire?
Sheet Lightning
wvlightning.com/types.shtml
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24. C.C. Hennon, UNC Asheville
Ball lightning
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25. Lightning Safety
C.C. Hennon, UNC Asheville
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26. Don’t talk on the telephone (cell OK) Don’t go for a walk
Don’t go golfing
Don’t talk on the telephone (cell OK)
Don’t go for a walk
Don’t find an isolated tree to stand under
If your hair stands on end, lightning is about to strike
Crouch down (don’t lay down) as low as possible
Stay away from the bathroom and windows
Cars are OK
C.C. Hennon, UNC Asheville
ATMS 103

27. Tornadoes
Rapidly rotating, small-scale winds that form within severe thunderstorms
Many different shapes; last anywhere from a few seconds to several hours
--spinning ice skater
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ATMS 103

28. Have occurred in all 50 U. S. states, but rare in Western U. S
Have occurred in all 50 U.S. states, but rare in Western U.S., Alaska, Hawaii
Form during every month of the year, but 75% form during months of March – July
Globally, U.S. has highest occurrence of tornadoes – WHY?
Anatomy of a tornado
Tornado Occurence
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29. Top Number: Number of tornadoes over a 25-year period (1953-2004)
Bottom Number: Average number per year per sq. km
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ATMS 103

30. Tornadic Winds and Classification
Tornadoes are classified on the Fujita Scale
F-0 : mph
F-1 : mph
F-2 :
F-3 :
F-4 :
F-5 : 200+
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31. F1 Tornado
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32. F2 Tornado
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33. F3 Tornado
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34. F4 Tornado
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35. F5 Tornado
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36. Tornado Formation Updrafts in thunderstorms must rotate
Called a mesocyclone
As mesocyclone stretches vertically, its diameter shrinks and it spins faster
Tornado forms within the mesocyclone and descends towards the surface (not understood why)
If condensation occurs within funnel, a funnel cloud will be seen
Tornado Formation
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ATMS 103

37. Observing Tornadoes
First sign (visually) of a tornado is the appearance of a wall cloud
Rotating cloud underneath the main cell
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ATMS 103
stormchasing.ca/_wsn/page11.html

38. Portable Radar Units (aka crazy people)
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39. Tornado Watch – Conditions are favorable for tornado formation
Tornado Watch – Conditions are favorable for tornado formation. Monitor local weather conditions and broadcasts
Tornado Warning – Tornado and/or funnel cloud and/or hook echo has been spotted in the area
Take cover immediately
Warning For Tornadoes
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ATMS 103

40. Anatomy of a Tornadic Thunderstorm
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41. Hurricanes A hurricane is a tropical storm with strong winds.
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42. Eye The center of the storm is called the eye. It is calm and serene.
No winds.
Eye
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43. Parts of a Hurricane anatomy of a hurricane
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44. How a Hurricane Forms
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