Thunderstorms and Lightning
Thunderstorms affect relatively small areas when compared with hurricanes and winter storms. All thunderstorms are dangerous. Every thunderstorm produces lightning, which kills more people each year than tornadoes. Heavy rain that leads to flash flooding, strong winds, hail and tornadoes are all dangers associated with thunderstorms.
The typical thunderstorm:
- Is 15 miles in diameter
- Lasts an average of 30 minutes
- Most likely to happen in the spring and summer months during the afternoon and evening hours, but can occur year-round and at all hours. Thunder and lightning can occasionally accompany snow or freezing rain.
Signs of a Thunderstorm
Watch for physical signs of approaching storms:
- Increasing wind
- Flashes of lightning
- Sound of thunder
- Static on your AM radio
Life Cycle of a Thunderstorm
- Towering cumulus cloud indicates rising air
- Usually little or no rain, and occasional lightning
- Lasts about 10 minutes
- 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
- Rainfall decreases in intensity
- Some thunderstorms produce a burst of strong winds
- Lightning remains a danger
Watches Versus Warnings
The National Weather Service continuously broadcasts updated weather warnings and forecasts that can be received by NOAA Weather Radios. Severe weather warnings are issued on a County. Check the weather forecast before leaving for extended periods outdoors.
Of the estimated 100,000 thunderstorms that occur each year in the United States, only about 10 percent are classified as severe. Your National Weather Service considers a thunderstorm severe if it produces hail at least three-fourths-inch in diameter, wind 58 mph or higher, or tornadoes.
- Severe thunderstorm watches are intended to heighten public awareness by alerting the public when and where severe thunderstorms are more likely to occur or when conditions are favorable for severe weather to develop. Watch the sky and stay tuned to know when warnings are issued.
- Severe thunderstorm warnings are issued when severe weather has been reported by spotters or indicated by radar. Warnings indicate imminent danger to life and property to those in the path of the storm.
Lightning results from the buildup and discharge of electrical energy between positively and negatively charged areas, which become separated by the rising and descending air within a thunderstorm. A cloud-to-ground lightning strike begins as an invisible channel of electrically charged air moving from the cloud toward the ground. When one channel nears an object on the ground, a powerful surge of electricity from the ground moves upward to the cloud and produces the visible lightning strike.
Thunder is the resulting shock wave caused by the rapid heating and cooling of air near the lightning channel. To estimate the distance in miles between you and the lightning flash, count the seconds between the lightning and the thunder and divide by five. "Heat lightning" is actually lightning from a thunderstorm too far away for thunder to be heard. However, the storm may be moving in your direction.
People most at risk to thunderstorms are those who are outdoors, especially those under or near tall trees, in or on water or on or near hilltops. Postponing outdoor activities if thunderstorms are imminent is your best way to avoid being caught in a dangerous situation. Remember—if you can hear thunder, you are close enough to the storm to be struck by lightning. Go to safe shelter immediately.
Lightning occurs in all thunderstorms, mostly within the cloud or between the cloud and ground. Most lightning casualties occur outdoors in the summer months, and during the afternoon and early evening.
- If you are outdoors:
- Move to a sturdy building or get inside a hardtop automobile and keep the windows up. If sturdy shelter is not available, find a low spot away from trees, fences and poles.
- If you are in the woods, take shelter under the shorter trees.
- Do not take shelter in small sheds, under isolated trees or in convertible automobiles.
- If you feel your skin tingle or your hair stand on end:
- Squat low to the ground on the balls of your feet.
- Place your hands on your knees with your head between them. Make yourself the smallest target possible
- Minimize your contact with the ground.
- If you are boating or swimming, get out of boats, away from water and to land.
- Telephone lines and metal pipes can conduct electricity. Unplug appliances not necessary for obtaining weather information. 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 the compressors.
- Rubber-soled shoes and rubber tires provide no protection from lightning. However, the steel frame of a hardtop vehicle provides increased protection if you are not touching metal. Although you may be injured if lightning strikes your car, you are much safer inside a vehicle than outside.
- Lightning-strike victims carry no electrical charge and should be attended to immediately. Contact your local American Red Cross chapter for information on CPR and first aid classes.
Revised November 4, 2016