1. Severe and Unusual Weather ESAS 1115
Spotter Training and Radar Meteorology
Part 1 – Introduction to Severe Thunderstorms
Prof. Paul Sirvatka
ESAS 1115 Severe and Unusual Weather

2. Convective Hazards Wind, Hail, Floods, Lightning, Tornadoes
Prof. Paul Sirvatka
ESAS 1115 Severe and Unusual Weather

3. Severe Thunderstorms are Severe
Many times, the media uses the word “severe” when the storm is something less than the actual meaning of “severe”.
Prof. Paul Sirvatka
ESAS 1115 Severe and Unusual Weather

4. Severe Thunderstorm Criteria
Hail greater than 1” in diameter
Winds greater than 50 kts (58 mph)
Tornadoes
Lightning and heavy rainfall, although posing a great threat to life, are not criteria used to determe whether or not a storm is severe
Prof. Paul Sirvatka
ESAS 1115 Severe and Unusual Weather

5. ESAS 1115 Severe and Unusual Weather
Lightning
Prof. Paul Sirvatka
ESAS 1115 Severe and Unusual Weather

6. ESAS 1115 Severe and Unusual Weather
Lightning
~25 million CG lightning strikes per year in the US making it the second deadliest aspect of thunderstorms
Prof. Paul Sirvatka
ESAS 1115 Severe and Unusual Weather

7. ESAS 1115 Severe and Unusual Weather
Lightning Safety
Lightning Stats
Lightning Safety Video
Lightning Safety Tips
Prof. Paul Sirvatka
ESAS 1115 Severe and Unusual Weather

8. Flash Floods – Turn Around Don’t Drown
Water is an incompressible fluid
1000 kg/m3
Results in buoyancy – 2 feet of water can move an SUV
Kills more people than lightning – approximately 100 annually in the US, 50% associated with drowning in vehicles
From , average annual cost is $3.7 billion
Flash flooding vs. river flooding
Prof. Paul Sirvatka
ESAS 1115 Severe and Unusual Weather

9. ESAS 1115 Severe and Unusual Weather
Flash Flood Threat
Prof. Paul Sirvatka
ESAS 1115 Severe and Unusual Weather

10. Flash Floods – Turn Around - Don’t Drown
Prof. Paul Sirvatka
ESAS 1115 Severe and Unusual Weather

11. ESAS 1115 Severe and Unusual Weather
Hail – Big Chunks o’ Ice
Prof. Paul Sirvatka
ESAS 1115 Severe and Unusual Weather

12. ESAS 1115 Severe and Unusual Weather
Tarrant County, TX May 5, 1995
10,000 people at Mayfest
Baseball hail – 10 miles wide 50 miles long
14 people killed by flooding and collapsed roofs
$2 billion (estimated)
Prof. Paul Sirvatka
ESAS 1115 Severe and Unusual Weather

13. ESAS 1115 Severe and Unusual Weather
We Know First Hand
Prof. Paul Sirvatka
ESAS 1115 Severe and Unusual Weather

14. ESAS 1115 Severe and Unusual Weather
Damaging Winds
Strong outflow from a thunderstorm enhanced by evaporative cooling and downward momentum transfer
Prof. Paul Sirvatka
ESAS 1115 Severe and Unusual Weather

15. ESAS 1115 Severe and Unusual Weather
Downbursts
A strong and potentially destructive thunderstorm downdraft
Microbursts are less than 2.5 miles in diameter
Macrobursts are greater than 2.5 miles
Prof. Paul Sirvatka
ESAS 1115 Severe and Unusual Weather

16. ESAS 1115 Severe and Unusual Weather
Rain Foot and Dust Foot
Prof. Paul Sirvatka
ESAS 1115 Severe and Unusual Weather

17. ESAS 1115 Severe and Unusual Weather
Dust Foot
Prof. Paul Sirvatka
ESAS 1115 Severe and Unusual Weather

18. ESAS 1115 Severe and Unusual Weather
Microbursts
Prof. Paul Sirvatka
ESAS 1115 Severe and Unusual Weather

19. ESAS 1115 Severe and Unusual Weather
Aviation Hazards
Prof. Paul Sirvatka
ESAS 1115 Severe and Unusual Weather

20. Danger on Takeoff and Landing
On the glide path, too much lift is generated with headwind gain
With the loss of a headwind, lift is limited
Prof. Paul Sirvatka
ESAS 1115 Severe and Unusual Weather

21. Beaufort Scale Winds based on visual observations Prof. Paul Sirvatka
ESAS 1115 Severe and Unusual Weather

22. ESAS 1115 Severe and Unusual Weather
First Microburst
Prof. Paul Sirvatka
ESAS 1115 Severe and Unusual Weather

23. Microburst within a Macroburst
Prof. Paul Sirvatka
ESAS 1115 Severe and Unusual Weather

24. ESAS 1115 Severe and Unusual Weather
Microbursts
Prof. Paul Sirvatka
ESAS 1115 Severe and Unusual Weather

25. ESAS 1115 Severe and Unusual Weather
Microburst Evolution
Prof. Paul Sirvatka
ESAS 1115 Severe and Unusual Weather

26. Tornado and Hail Climatology
There are more than 1000 tornadoes in the US per year. Hail results in over $1 billion of damage annually.
Harold Brooks - NSSL
Prof. Paul Sirvatka
ESAS 1115 Severe and Unusual Weather

27. 61 Years of Tornado Tracks
Prof. Paul Sirvatka
ESAS 1115 Severe and Unusual Weather

28. Tornado Frequency All Tornadoes Significant Tornadoes Deadly Tornadoes
Prof. Paul Sirvatka
ESAS 1115 Severe and Unusual Weather

29. ESAS 1115 Severe and Unusual Weather
Tornado Threats
Violently rotating column of air in contact with the ground and pendant from a cumulonimbus cloud (thunderstorm)
Tornadoes are ranked on the Enhanced Fujita damage scale: from EF0-EF5
Appearance is deceiving with small tornadoes sometimes having high destruction potential and large tornadoes having low potential
Prof. Paul Sirvatka
ESAS 1115 Severe and Unusual Weather

30. ESAS 1115 Severe and Unusual Weather
EF0, EF1 – Weak Tornadoes
Approximately 70% of tornadoes are in this category
Well-built houses offer adequate safety for these tornadoes
Cars and mobile homes are still very vulnerable to these tornadoes
Wind speeds: 65 – 110 mph
Prof. Paul Sirvatka
ESAS 1115 Severe and Unusual Weather

31. EF2, EF3 – Strong Tornadoes
Approximately 28% of all tornadoes are considered strong
Well-built houses will be severely damaged but still can provide adequate life-protection
Wind speeds: 111 – 165 mph
Prof. Paul Sirvatka
ESAS 1115 Severe and Unusual Weather

32. EF4, EF5 – Violent Tornadoes
Only 2% of all tornadoes are violent
Will completely level a well-built house
The last EF-5’s to hit the US were May 3, 1999 (Moore, OK,) May 24, 2007 (Greensburg, KS,) and May 25, 2008 (Parkersburg, IA.)
Wind speeds: >200 mph
Prof. Paul Sirvatka
ESAS 1115 Severe and Unusual Weather

33. ESAS 1115 Severe and Unusual Weather
Rating a Tornado
Prof. Paul Sirvatka
ESAS 1115 Severe and Unusual Weather

34. Wind Damage vs Tornado Damage
Microburst
Damage is divergent
Large or diffuse area
No signs of rotation
Tornado
Damage is convergent
Narrow path
Rotation about vertical axis
Prof. Paul Sirvatka
ESAS 1115 Severe and Unusual Weather

35. ESAS 1115 Severe and Unusual Weather
Swirl Marks
Prof. Paul Sirvatka
ESAS 1115 Severe and Unusual Weather