NWS CR >> WFO Louisville >> Preparedness >> Tornadoes: Nature's Most
Violent Storms
Environmental Clues
Tornadoes are often preceded by a dark,
often greenish sky, large hail, and often a loud roar, similar to a
freight train. In the southern states, however, tornadoes frequently
occur without the presence of large hail.
Most strong and violent tornadoes occur with "supercell"
thunderstorms. A supercell storm is characterized by intense
rotation within the storm. Typically, this area of rotation occurs
in the south side of the storm. Visually, a low-hanging cloud base
with rotation is often seen. This area may or may not be visible
since rain sometimes wraps around the area of circulation.
Some tornadoes appear as a visible funnel extending only
partially to the ground. Look for signs of debris below the visible
funnel. |
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Rotating wall cloud with very dark sky in the background, near
Lahoma, Oklahoma. Note the greenish hue.
(Greg Stumpf) |
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Tornado near Alma, Nebraska, showing visible condensation only
partially to the ground. But, how can you tell it is a tornado? Note
the swirl of dust near the ground, and the visible funnel. (Gene
Rhoden) |
Tornado nearly obscured by heavy rain near McClean, Texas. The
red circle is where the tornado is located.
(Mike Emlaw) |
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Photo of a supercell thunderstorm looking east. The presence of
an overshooting top above the anvil suggests a very intense storm
with an increased potential of being severe. (Howard Bluestein,
University of Oklahoma) |
Photo of a tornado-producing supercell thunderstorm, looking
west. The tornado is located just south of the precipitation region.
(Alan Moller, NWS) |
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In addition to tornadoes,
thunderstorms often produce other hazards. In many cases, these
other hazards occur in conjunction with tornadoes.
- Flash Floods/Floods
- The number ONE thunderstorm-related killer -- averages 146
deaths annually.
- Lightning
- Kills 75 to 100 people each year
- Damaging Straight-Line Winds
- Can reach speeds of 140 mph
- Large Hail
- Often the size of golf balls and occasionally can reach
grapefruit size. Hail causes several hundred million dollars
in damage annually to property and crops.
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The result of a flash flood at Shadyside, Ohio, June 14, 1990. (NOAA/NWS) |
Large hail near Altus, Oklahoma. Some of the hailstones are
larger than golfballs. (NOAA/NWS) |
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A stunning flash of lightning. (Bill Bunting, NWS) |
'Tornadoes: Nature's Most Violent Storms' was developed by the
National Oceanic and Atmospheric Administration (NOAA)/National Weather
Service (NWS) in cooperation with the American Red Cross and the Federal
Emergency Management Agency (FEMA). It is designed to assist in
heightening public awareness and understanding the dangers associated with
tornadoes. The package provides an introduction to tornadoes and their
impact, discusses tornado development and occurrence, and describes safety
information for homes, schools, places of work, and outdoors. In addition,
basic environmental clues are presented.
Individual use of the pictures within these presentation must have prior
approval from the credited source. |
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