1. How to Recognize, Identify, and Report Severe Weather
Severe Weather Guide
How to Recognize, Identify, and Report Severe Weather

2. Definitions and Terms
Watch: conditions are favorable for severe weather
Warning: severe weather is currently occurring in the area
Watches and warnings are issued for: severe thunderstorms, hail, flash floods, and tornadoes

3. Thunderstorms Every Thunderstorm Needs:
Moisture
Unstable Air (warm air to rise rapidly)
Lift (cold front)
There are three stages in the life cycle of a thunderstorm
Developing (Cumulus) stage
Mature stage
Dissipating stage

4. Thunderstorms Developing Stage Rising cumulus clouds; strong updraft
Little if any precipitation
Lasts about 10 minutes
Occasional lightning

5. Thunderstorms Mature Stage Updraft and downdraft
Most likely time for heavy rain, frequent lightning, strong winds, and hail
Tornado development is possible
Averages minutes, but can last a few hours

6. Thunderstorms Dissipating Stage Weakened updraft
Rainfall lessens in intensity
Lightning and strong winds remain a threat

7. Types of Thunderstorms
Single Cell (Pulse):
Generally weak, short lived, and poorly organized
Multicell Cluster:
Most common type
Series of cells moving as one unit
Multicell Line:
AKA “Squall Line”
Long line of storms with gust front at leading edge
Supercell:
Very strong and produce severe weather

8. Types of Thunderstorms
A thunderstorm is classified as severe if it has any of the following characteristics
Hail greater than 1” in diameter (dime size)
Winds greater than 58 miles per hour
Tornado

10. Single Cell Storm 20-30 minutes Rarely turn severe
Heavy rainfall and weak tornadoes are still possible
Poorly organized

11. Single Cell Storm

12. Multicell Cluster Storm
Most common type of thunderstorm
Each cell in the cluster is at a different stage of the thunderstorm life cycle
Each cell may last 20 minutes, but each cluster can last several hours
Heavy rain, downbursts, moderate sized hail, occasional weak tornadoes

13. Multicell Cluster Storm

14. Multicell Cluster Storm

15. Multicell Line Storm Squall Line
Long line of storms with a continuous, well developed gust front at leading edge of the line
Heaviest rain is at center of line
Produce heavy rain, hail, and tornadoes
Strong downbursts can cause line to bend and become a “bow echo”

16. Multicell Line Storm

17. Multicell Line Storm

18. Multicell Line Storm – Bow Echo

19. Multicell Line Storm – Bow Echo

20. Supercell Thunderstorm
Rarest type of thunderstorm, but the most dangerous
The updraft rotates (called mesocyclone)
Large hail
Heavy downpours
Strong downbursts
Strong to violent tornadoes

21. Supercell Thunderstorm (w/o Tornado)

22. Supercell Thunderstorm (w/Tornado)

23. Supercell Thunderstorm (w/Tornado)

24. Supercell Thunderstorm

25. Dangers of Thunderstorms
Flash Floods
Lightning
Hail
Downbursts
Tornadoes

26. Flash Floods #1 cause of death associated with thunderstorms
An average of 140 fatalities every year (in US)
Definition: a rapid rise in water (creeks, streams, drainage ditches) within 12 hours of a period of heavy rain
As little as 6 inches can knock a human over
Two feet of water can move a car
“Turn Around, Don’t Drown”
Get to higher ground immediately

28. Lightning Lightning occurs in all thunderstorms
Causes an average of 80 fatalities and 300 injuries per year (in the US)
Lightning strikes the tallest object
If caught outside crouch down in a ball
30/30 Rule
Go indoors if you hear thunder before counting to 30 after you see lightning
Wait inside for 30 minutes after you last hear thunder

30. Hail
Rarely causes fatalities, but causes significant damage to property and crops
Can fall at rates up to 100 miles per hour
Created by strong updrafts in thunderstorm

31. Hail Sizing Chart Pea 0.25” Penny/Dime (Severe Criteria) 0.75”
Nickel ”
Quarter ”
Half Dollar ”
Ping Pong Ball ”
Golf ball ”
Hen Egg ”
Tennis Ball ”
Baseball ”
Grapefruit ”
Softball ”

32. Downbursts
A strong downdraft with an outrush of damaging winds at the surface
Winds can reach 100 miles per hour or more
Straight line winds
Winds speed and direction can change rapidly

33. Downbursts

34. Downbursts Wind Speed Estimates (mph)
25-31: large branches in motion; whistling in telephone wires
32-38: whole trees in motion
39-54: twigs break off of trees; wind impedes walking
55-72: damage to chimneys and TV antennas; pushes over shallow rooted trees
73-112: peels surface off roofs; windows broken; trailer houses overturned
113+: roofs torn off houses; weak building destroyed; large trees uprooted

35. Tornado “Look-A-Likes”
Several cloud formations are associated with a thunderstorm that can be confused with an actual tornado
Wall clouds
Shelf clouds
Roll clouds
A roll cloud is similar to a shelf cloud, but it is detached from the main “parent cloud” whereas a shelf cloud is part of the main storm cloud
Scud Clouds
Detached and wind torn – similar shape to wall/funnel clouds

36. Wall Clouds versus Shelf Clouds
Suggest Inflow/Updraft
Suggest Outflow/Downdraft
Maintain position with respect to rain
Move away from rain
Slope upward away from precipitation
Slope downward away from precipitation

37. Wall Cloud

38. Wall Cloud What is the tornado potential for a wall cloud?
It will be consistent, lasting minutes
It will have persistent rotation
Strong winds will blow into the wall cloud from the south or southeast (25-35 mph)
It will exhibit evidence of rapid vertical motion
These are rules of thumb – there are always exceptions!

39. Shelf Cloud

40. Roll Cloud

41. Scud Cloud

42. Tornadoes
A tornado is a violently rotating column of air in contact with the ground extending from a thunderstorm
May appear transparent until dirt and debris are picked up in the vortex or until a condensation cloud forms
A tornado that forms over a body of water is called a waterspout

43. Tornadoes Tornadoes can occur at any time, any day, and in any state
They are most common
In tornado alley: Texas north to Nebraska and east to Indiana
During the spring and summer months
During the late afternoon and early evening

44. Average Number of Tornadoes Per Year

47. Average Number of Tornadoes Per Month

48. Tornadoes By Hour of Day

49. Tornado Life Cycle
1. Funnel Cloud: extending from wall cloud, but not yet in contact with the ground
2. Mature Tornado
3. Rope Stage: the dissipating stage
Tornadoes are dangerous during all stages

50. Funnel Cloud

51. Mature Stage

52. Rope Tornado

53. Tornado Characteristics
Weak Tornadoes
Strong Tornadoes
Violent Tornadoes
% of Tornadoes
88%
11%
<1%
% of Tornado Deaths
<5%
~30%
70%
Duration
1-10+ minutes
20+ minutes
Can exceed 1 hour
Path Length
Up to 3 miles
15+ miles
50+ miles
Winds
<110 mph
mph
>205mph

55. Tornadoes
Tornadoes are always dangerous regardless of shape, size, or color
Large cities and mountains are just as prone to tornadoes as wide open fields
Average tornado speed is 30mph, but they can move as fast as 70mph
Do not attempt to outrun a tornado, find shelter immediately

56. Tornado Fujita Scale F Scale Type Strength Winds Gale Weak 40-72 mph 1
Gale
Weak
40-72 mph 1
Moderate
mph 2
Significant
Strong
mph 3
Severe
mph 4
Devastating
Violent
mph 5
Incredible
mph

57. Severe Weather Alerts
During periods of severe weather it is important to keep an eye on the sky
Local television, radio, and the Internet are vital sources of information
A S.A.M.E NOAA weather radio is essential for immediate watches and warnings