Presentation by Senior Forecaster John Lewis

1. What Makes the Weather Tick/
Considering Your Safety
John Lewis
Senior Forecaster
National Weather Service
Little Rock, Arkansas

2. Rain So Far (04/18)

3. Rain In April

4. Rain In April

5. When We Are Open
Weather never stops, so we are open
24 hours a day/7 days a week (even on
Christmas, Thanksgiving, etc).

6. NWS in Arkansas
We are one
of five
forecast
offices that
serve the
state of
Arkansas.

7. NWS in United States
There are 122 forecast offices nationwide.

8. NWS
Where Are We?

9. Where Are We?Radar
NWS

10. A Look Inside

11. A Look Inside

12. An Example of Radar Data

13. How Radar Works

14. Billion Dollar Weather Disasters

15. 2018 Storm
Reports

16. To protect life and property by issuing
timely warnings (i.e. for tornadoes, severe
thunderstorms, flash flooding, etc).
Our Mission
Tornado Warning
Severe Thunderstorm Warning

17. Severe thunderstorms produce 58 mph
winds or greater, quarter size hail or
larger, and/or a tornado.
Severe Weather
Tornado Warning
Severe Thunderstorm Warning

18. Watch Vs. Warning
Watches are issued for a large area for
several hours and mean “maybe”. Warnings
are issued for a small area for less than an
hour and mean “yes”.

19. Focus on the
isolated storm
ahead of the
line.
Radar on a Busy Day

20. Here is a close-up of the storm.
Zooming in on a Supercell

21. Rotation in a Supercell
Here is a close-up of the storm.

22. What Makes a Supercell
Speed Shear – Winds pick up with height.
Makes storms move fast and tilt in the
vertical.
Directional Shear – Winds turn with height.
Makes storms rotate in the vertical.

23. Speed Shear
Storm tilts with height. Precipitation and
cool downdrafts are downstream of warm
and moist updrafts feeding the storm.

24. Speed Shear

25. Speed Shear

26. Speed Shear

27. Speed Shear

28. Directional Shear

29. Directional Shear
Assume
this is a
column of
air along the
ground.

30. There is
wind shear
(south winds
near the
ground
and west
winds aloft).
South
Winds
West
Winds
Directional Shear

31. This causes
the column
to rotate.
Directional Shear

32. If the column
gets ingested
into a storm,
it will become
vertical.
Directional Shear

33. The storm
becomes a
“supercell”
(rotating
updrafts).
Rotating
Updrafts
Directional Shear

34. If you are the
radar, winds
toward you
(inbound) are
green and
away from you
(outbound) are
red.
Rotating
Updrafts
Inbound Outbound
Directional Shear

35. Directional Shear
Speeding up
the video, the
storm turns.

36. Tornado Video

37. Tornado on April 27, 2014
At 743 pm CDT, the WSR-88D (Doppler Weather
Radar) showed strong rotation to the southwest
Of Vilonia (Faulkner County). A Dual-Pol
Correlation Coefficient (CC) image indicated a
Tornado Debris Signature (TDS).
Rotation Debris

38. Tornado on April 27, 2014
Given information from the radar, and also
from trained storm spotters, a rare
“Tornado Emergency” was declared.

39. Hiding From Tornadoes
A tornado removed the roof from
this home, and exterior walls were
blown out.

40. Hiding From Tornadoes
These are good places (interior
rooms away from windows). You
put more TIME between you and
the tornado.

41. Hiding From Tornadoes
Mobile homes are often blown over
and rolled quickly.

42. This is a bad place (a bridge
directly exposed to the wind).
Hiding From Tornadoes

43. The vast majority
of tornadoes are
weak, and cause
little damage.
Big Tornadoes are Rare

44. Big Tornadoes are Rare
Since 2000, only 3 of 739 tornadoes
were rated at least F4/EF4. These
tornadoes caused 33 of 72 fatalities.

45. When Do Tornadoes Occur?

46. When Do Tornadoes Occur?

47. Tornado
damage is
often confused
with damage
caused by
straight-line
winds (i.e. bow
echoes).
Tornadoes or Straight-Line Winds

48. Bow echoes are
often long-lived,
and can travel
several hundred
miles. Tornadoes
are mostly short-
lived.
A Large Swath of Damage

49. Bow echoes look nothing like
tornadoes, as witnessed at Sherwood
(Pulaski County) on June 12, 2009.
An Incoming Bow Echo

50. Damaging Straight Line Winds

51. Damaging Straight Line Winds

52. 1014 pm CDT
May 30
to
247 am CDT
May 31
Flash Flood
Rain is accumulating faster than draining.

53. Flood Photos
04/29/2006 – 12:22 pm
Little Rock - Landers Toyota Scion

54. Flood Photos
Little Rock - Landers Toyota Scion
04/29/2006 – 12:23 pm

55. Flood Photos
Little Rock - Landers Toyota Scion
04/29/2006 – 12:25 pm

56. Flood Photos
Little Rock - Landers Toyota Scion
04/29/2006 – 12:29 pm

57. Flood Photos
Little Rock - Landers Toyota Scion
04/29/2006 – 12:49 pm

58. Don’t Drive Through Water

59. What About Lightning?

60. Lightning Deaths

61. Three Ways to Get Struck
Direct Side Flash
Ground

62. Lightning Safety

63. Weather Fatality Statistics

64. Heat Index

65. Heat Index
At higher temperatures/humidity levels,
the body sweats less efficiently, and
you have trouble cooling off (i.e. you
overheat faster).
Heat Advisory: Heat index value 105
degrees or greater and/or temperature
103 degrees or greater.
Excessive Heat Warning: Heat index
value 110 degrees or greater and/or
temperature 105 degrees or greater.

66. Heat Safety

67. Receiving Headlines Via Map

68. Outdoor Sirens/TV/Radio

69. NOAA Weather Radio
There are 25
transmitters in
Arkansas that
broadcast
forecast
information and
warnings.
Cleburne
County SAME
Code: 005023
Fox:
162.450 MHz
Russell:
162.400 MHz

70. Wireless Emergency Alerts
https://www.weather.gov/wrn/wea

71. Wireless Emergency Alerts
Third party alert services…
https://www.weather.gov/subscribe/

72. Make a Plan
(1) Figure out the weather concern for
the day (i.e. severe storms, heat, etc).
(2) Designate someone to monitor the
weather concern.
(3) Take action and inform the group if
thresholds are met.

73. Where to Find Us
https://www.weather.gov/lzk

74. The End
Thank you for coming!!!