All About Thunderstorms and Lightning..

What is a thunderstorm?

A thunderstorm is a storm with lightning and thunder, produced by a cumulonimbus cloud, usually producing gusty winds, heavy rain and sometimes hail.

The typical thunderstorm is 15 miles in diameter and lasts an average of 30 minutes. Nearly 1,800 thunderstorms are occurring at any moment around the world.

Are thunderstorms dangerous?

All thunderstorms are dangerous. About 10% of the thunderstorms that occur each year in the United States are classified as severe. (A thunderstorm is considered severe if it produces hail at least 3/4 inch in diameter, winds 58mph or greater or tornadoes.)

What are the dangers associated with thunderstorms?

Every thunderstorm produces lightning, which kills more people each year than tornadoes. Heavy rain from thunderstorms can lead to flash flooding (which is the number one thunderstorm killer.) Strong winds, hail, and tornadoes are also dangers associated with some thunderstorms.

Flash Floods/Floods

      • The number ONE thunderstorm killer...nearly 140 fatalities each year.
      • Most flash flood deaths occur at night and when people become trapped in automobiles.

Lightning

      • Occurs with ALL thunderstorms.
      • Averages 93 deaths and 300 injuries each year.
      • Causes several hundred million dollars in damage to property and forests annually.

Straight-line Winds

      • Responsible for most thunderstorm wind damage.
      • Winds can exceed 100 mph!
      • One type of straight-line wind, the downburst, can cause damage equivalent to a strong tornado and can be extremely dangerous to aviation.
      • During the summer in the western states, thunderstorms often produce little rain but very strong wind gusts and dust storms.

Large Hail

      • Causes nearly $1 billion in damage to property and crops annually.
      • Costliest United States hailstorm: Denver, Colorado, July 11, 1990. Total damage was $625 million.

Tornadoes

      • Nature's most violent storms.
      • Winds can exceed 200 mph.
      • Result in an average of 80 deaths and 1,500 injuries each year.
      • Most fatalities occur when people do not leave mobile homes and automobiles.

How does a thunderstorm form?

Every thunderstorm needs:

    • 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 help form thunderstorms.

When do most thunderstorms occur?

Thunderstorms are most likely to occur in the spring and summer months and during the afternoon and evening hours but they can occur year-round and at all hours of the day or night.

    • Along the Gulf Coast and across the southeastern and western states, most thunderstorms occur during the afternoon.
    • Thunderstorms frequently occur in the late afternoon and at night in the Plains states.
    • Thunder and lightning occasionally accompany snow or freezing rain. During the blizzard of March 1993, lightning resulted in power outages near Washington, D.C.!

Who is at risk from Thunderstorms?

  • People who are outdoors, (especially under or near tall trees; in or on water; or on or near hilltops) are at risk from lightning.
  • People who are in automobiles when flash flooding occurs near them are at risk from flash floods.
  • People who are in mobile homes and automobiles are at risk from tornadoes.

What is Lightning?

The action of rising and descending air within a thunderstorm separates positive and negative charges. Water and ice particles also affect the distribution of electrical charge. Lightning results from the buildup and discharge of electrical energy between positively and negatively charged areas. Most lightning occurs within the cloud or between the cloud and ground.

    • The average flash could light a 100-watt light bulb for more than 3 months. he air near a lightning strike is heated to 50,000øF hotter than the surface of the sun! The rapid heating and cooling of air near the lightning channel causes a shock wave that results in thunder.
    • Your chances of being struck by lightning are estimated to be 1 in 600,000 but could be reduced by following safety rules. Most lightning deaths and injuries occur when people are caught outdoors.Most lightning casualties occur in the summer months and during the afternoon and early evening.
    • Many fires in the western United States and Alaska are started by lightning. In the past decade, over 15,000 lightning-induced fires nationwide have resulted in several hundred million dollars a year in damage and the loss of 2 million acres of forest.

Which way does lightning travel?

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!

What are some myths concerning Lightning?

MYTH: If it is not raining, then there is no danger from lightning.
FACT: Lightning often strikes outside of heavy rain and may occur as far as 10 miles away from any rainfall.

MYTH: The rubber soles of shoes or rubber tires on a car will protect you from being struck by lightning.
FACT: Rubber-soled shoes and rubber tires provide NO protection from lightning. However, the steel frame of a hard-topped 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.

MYTH: People struck by lightning carry an electrical charge and should not be touched.
FACT: Lightning-strike victims carry no electrical charge and should be attended to immediately.

MYTH: "Heat lightning" occurs after very hot summer days and poses no threat.
FACT: What is referred to as "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!

How do I know when a thunderstorm is about to occur?

When skies darken or thunderstorms are forecast, look AND listen for

    • Increasing wind.
    • Flashes of lightning. (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.)
    • Sound of thunder.
    • Static on your AM radio.

How does the National Weather Service warn the public about thunderstorms?

When conditions are favorable for severe weather to develop, a severe thunderstorm WATCH is issued by the National Weather Service. Weather Service personnel use information from weather radar, satellite, lightning detection, spotters, and other sources to issue severe thunderstorm warnings. WARNINGS for areas where severe weather is imminent. The severe thunderstorm warnings are passed to local radio and television stations and are broadcast over local NOAA Weather Radio stations serving the warned areas. These warnings are also relayed to local emergency management and public safety officials who can activate local warning systems to alert communities.

What is the difference between a severe thunderstorm warning and a severe thunderstorm watch?

  • SEVERE THUNDERSTORM WATCH: tells you when and where severe thunderstorms are more likely to occur. Watch the sky and stay tuned to know when warnings are issued. Watches are intended to heighten public awareness and should not be confused with warnings.
  • SEVERE THUNDERSTORM WARNING: 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. Also listen for Tornado Watch or Warning and Flash Flood Watch or Warning.

Where can I get the latest watches and warningsfor my local area?

Besides the local media and NOAA Weather Radio there are many internet sites that contain the latest watches and warnings in your area. The National Weather Service - Interactive Weather Information Network (IWIN) is The National Weather Service's Internet data source
Remember : REFRESH / RELOAD YOUR BROWSER TO GET THE LATEST DATA !

What do I do to prepare:

Where can I obtain more information about thunderstorms and lightning and related subjects?