Thunderstorm Dangers

Thunderstorms are in the forecast. That usually means the air near the ground is warm and moisture laden, while the air aloft is pretty cold.  Bring in a cold front and wham, you get a thunderstorm.

News 11 Meteorologist Mike Stone says the typical thunderstorm produces a brief period of heavy rain, and lasts an average of 30 minutes. While the thunder won't hurt you, lightning will. Other hazards can include hail, heavy rain, flooding, and strong winds.

According to the National Weather Service, a severe thunderstorm is when winds reach or exceed 57.5 miles per hour or produces dime-sized hail or larger.

Thunderstorms need three things to form: moisture, unstable air and lift. One begins to form when the warm, humid air rises up from the ground in an updraft. The air cools and condenses into clouds. When the condensation becomes heavy it falls as rain dragging "down" air forming downdrafts.

At this point -- the downdrafts and updrafts coexist making this the storm's most violent period. But eventually the downdrafts choke off the updrafts -- cutting off the storm's source of energy and bringing the storm to an end.

Out of the 100,000 thunderstorms that occur in the US each year, only 10%are severe thunderstorms.  A typical thunderstorm is 15 miles in diameter and lasts for about 30 minutes.

Knowing basic terminology is the first step in staying safe in a thunderstorm:

  • A SEVERE THUNDERSTORM WATCH is issued by the Storm Prediction Center and means conditions are favorable for the development of thunderstorms that will exceed severe limits.
  • A SEVERE THUNDERSTORM WARNING is issued by the local office of the National Weather Service. They use radar, satellite, lightning detectors, and spotters to follow thunderstorms and issue warnings for counties when severe weather is imminent.

Here are some safety tips for when a thunderstorm is approaching:

  • If you can hear thunder, you are close enough to the storm to be struck by lightning. Seek safe shelter immediately.
  • DO NOT seek shelter in small sheds, under isolated trees, or in convertible automobiles. Move to a sturdy building or car.
  • If lightning is occurring and a sturdy shelter is not available, seek shelter inside a hard top car and keep windows up.
  • Stay away from water, this includes boats.
  • Telephone lines and metal pipes can conduct electricity. Avoid using the telephone or any electrical appliances. Use phones ONLY in an emergency.
  • Do not take a bath or shower. Turn off air conditioners. Power surges from lightning can overload compressors.
  • If you are boating or swimming, get to land and find shelter immediately

Lightning is one of the most dangerous parts of a thunderstorm.  Here are some interesting facts to remember:

  • Lightning strikes the earth 100 times every second and kills around one hundred people every year in the United States.
  • Thunderstorms produce lightning and often it strikes outside heavy rain. In fact, lightning can occur as far as 10 miles away from any rainfall.
  • About two thirds of lightning occurs from cloud to cloud.
  • Lightning occurs from the build up of positively and negatively charged ions.
  • When there becomes a large difference between the two, a bolt of lightning will occur to balance things out.
  • If you feel your skin tingle or your hair stand on end, squat low to the ground on the balls of your feet. A lightning strike may be imminent.

The other big killer in thunderstorms is flash flooding.  The term "flood" refers to a long term event that is many times associated with general rains that last for several days. The rains eventually drain into rivers and streams and fill them with too much water. The flooding can actually develop after the rain has stopped.

The difference between a flood and a flash flood is that flash floods result from heavy, localized rainfall from slow moving thunderstorms. This often occurs around small creeks and streams that overflow during the heavy rainfall.

You may hear the terms "Flash Flood Watch" or "Flash Flood Warning," here is the difference:

  • A FLASH FLOOD WATCH means conditions are favorable for heavy rains in a short amount of time that may lead to flooding.
  • A FLASH FLOOD WARNING means heavy rain is causing areas to flood quickly and you should seek shelter if it is near you.

There are several safety rules that you can incorporate into your severe weather plan when it comes to flash flooding:

  • Do not cross a flowing stream where the water is above your ankles. Moving water carries a tremendous amount of energy and you can be quickly swept off your feet.
  • Never try to cross a water-filled roadway where the depth is not known. If you happen to get caught in an area of rising water and your vehicle stalls, leave it. The rising water maybe powerful enough to sweep the vehicles and its occupant away.
  • Be especially cautious at night. You often arrive upon a flood area without notice.
  • Heavy rains are often channel into ditches and gullies and this can turn an area into a quick and fast rising stream of water in a matter of minutes. This means never camp on low ground next to these areas, since it could catch you off guard while you're sleeping.

Posted by AEB