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Severe Weather Awareness - Thunderstorms and Lightning

...the underrated killers!


Thunderstorms affect relatively small areas when compared with hurricanes and winter storms. The typical storm is 15 miles in diameter and lasts an average of 30 minutes. Nearly 1,800 thunderstorms are occurring at any time around the world - that's nearly 16 million thunderstorms each year!

Despite their small size...all thunderstorms are dangerous. Every thunderstorm produces lightning...which kills more people each year than tornadoes.
  • Occurs with all thunderstorms

  • Averages 93 deaths and 300 injuries nationwide each year

  • Causes several hundred million dollars in property damage and forests each year.

 Millions of dollars in property loss are the result of lightning caused fires
Photo by Phoenix Gazette

Heavy rains from thunderstorms can lead to flash flooding.
  • The number one thunderstorms killer...nearly 140 deaths each year nationwide.

  • Most flash flood deaths occur at night and when people become trapped in cars.

 

Flood waters up to a car's windows
Photo by David Vann, The Sentinel-Record
Hot Springs AR

Damaging straight-line winds are another threat posed by thunderstorms...
  • Responsible for most thunderstorm wind damage
  • Winds can exceed 100 miles per hour! 

Trees blown down in straight lines by microburst winds
Photo by: Dr. T. Theodore Fujita

Hundreds of trees were blown down by straight-line winds in Sawyer County Wisconsin in July 1977

One type of straight-line wind ... the downburst or microburst ... can cause damage equivalent to a strong tornado and can be extremely dangerous to aviation. 

Hail is another costly threat posed by thunderstorms
  • Causes nearly $1 billion in damage to property and crops each year
  • According to NOAA, the Kansas City hail storm on April 10, 2001 was the costliest hail storm in the U.S. which caused damages of an estimated $2 billion.

 

Large hailstone
Photo from
National Center for Atmospheric Research

Tornadoes are nature's most violent storms

  • Winds can exceed 200 miles an hour. 

 

  • Tornadoes cause an average of 80 deaths and1,500 injuries nation-wide each year. 

 

  • Most deaths occur when people do not leave mobile homes and automobiles.

A large tornado
Photo by Greg Stumpf

How do thunderstorms develop?

Every thunderstorm needs three ingredients:
  • Moisture - to form clouds and rain
  • Unstable air - relatively warm air that can rise
    rapidly 
  • Lift - fronts, sea breezes, and mountains are
    capable of lifting air to form thunderstorms.

Winds bring moisture from the ocean over the land area...lift is provided by approaching cooler, drier, more dense air (a cold front)

In the developing stage...rising warm air carries moisture aloft into cooler air where the moisture condenses and builds the clouds vertically.
  • Towering cumulus clouds indicate rising air
  • Usually little if any rain during this stage 
  • Lasts about 10 minutes 
  • Occasional lightning during this stage 
A developing thunderstorm with vertical growth
In the mature stage...
  • Most likely time for hail, heavy rain, frequent lightning, strong winds and tornadoes 
  • Storm occasionally has a black or dark green appearance 
  • Lasts an average of 10 to 20 minutes but may last much longer in some storms 
A thunderstorms in the mature stage

In the dissipating stage...rain cooled air flowing out of the thunderstorms cuts of the supply of warm unstable rising air

  • Rainfall decreases in intensity

  • Some thunderstorms produce a burst of strong winds during this stage 

  • Lightning remains a danger during this stage 

A thunderstorm in the dissipating stage
Where are thunderstorms most likely? Across much of Georgia and in central and southern South Carolina there are an average of 50 to 70 days with thunderstorms each year. From the Pee Dee region to the Upstate of South Carolina there are an average of 30 to 50 days each year with thunderstorms.

Thunderstorms are most likely to happen in the spring and summer  and during the afternoon and evening hours - but in South Carolina and Georgia thunderstorms can develop year-round and at all
hours.

Thunderstorms distribution

Thunderstorms are common during the spring and summer across the southeastern U.S.

The National Weather Service considers a thunderstorm severe only if it produces ...

Damaging Wind Gusts
58 miles per hour (50
knots) or higher

or

Large Hail
3/4 inch in diameter
(penny size) or larger

or

Tornadoes

Of the estimated 100,000 thunderstorms that occur each year in the United States, only 10 percent (or 10,000) are classified as severe.

The National Weather Service issues watches and warnings for severe thunderstorms

A SEVERE THUNDERSTORM WATCH means conditions are favorable for thunderstorms to
become severe...or severe thunderstorms to move into the watch area. Watches are intended to heighten public awareness of the possible severe weather threat. Keep an eye on the sky and stay tuned to NOAA Weather Radio or local radio, television, or cable to know when severe weather warnings are issued for your area.

A SEVERE THUNDERSTORM WARNING means a severe thunderstorms poses an imminent danger to life and property to those in the path of the storm. When severe weather is indicated by weather radar, or is reported by trained SKYWARN Severe Weather Spotters or law enforcement
officials a warning is issued immediately.

With new equipment capable of monitoring and tracking lightning, stay tuned to official news sources for latest information.

Severe Thunderstorm warnings are sent to local radio and television stations and are broadcast over your local NOAA Weather Radio serving the warning area. These warnings are also relayed to local emergency management and public safety officials who can activate local warning systems to alert communities to the danger.

Contact us if you'd like a free copy of Thunderstorms...Tornadoes...Lightning...Nature's Most Violent Storms - a preparedness brochure produced by the National Weather Service, Federal Emergency Management Agency, and the American Red Cross.

Related Web Sites on Lightning and Lightning Safety: