Even without a tornado, a severe thunderstorm can be damaging and life-threatening event. Deaths and injuries occasionally occur from strong thunderstorm winds. Thunderstorms also account for millions of dollars in property damage. Also large hail can be responsible for tremendous property damage.

The National Weather Service defines a thunderstorm as "severe" when wind speeds reach 58 mph or stronger and/or hail is produced that is 3/4 inch in diameter or larger and/or tornado is produced.

Downward rushing currents of air, or downdrafts, occur along the leading edge of almost all thunderstorms and along the trailing edge as well, in some cases. This process, the same that can bring a welcome cooling breeze on a hot summer day, can also produce winds as damaging as those of a tornado. Strong localized downdrafts are called "downbursts". These intense concentrations of sinking air fan out upon striking the earth's surface and produce damaging winds. They may be accompanied by a "roaring sound". Thunderstorms that produce downbursts typically produce several in succession of various sizes and intensities. There may be a well defined damage path similar to that of a tornado or concentrated damage may occur in one spot.

Downdraft winds from thunderstorms often reach destructive force in Mississippi. These damaging winds are called "straight-line winds", and can have windspeeds up to 60 mph...and can even reach or exceed 100 mph on occasion. What mkes these winds so damaging is the rapid increase in local windspeeds when downbursts strike. Winds that rapidly jump from 10 to 60 mph can produce more damage than a sustained 60 mph wind. Frequently, damage that is attributed to tornadoes is actually due to the straight-line winds of a downburst.

In Mississippi the frequent occurrence of downburst winds makes it imperative that the threat of non-tornadic severe thunderstorms be taken seriously as severe thunderstorms with tornadoes.

Large hailstones can develop within strong thunderstorm updrafts. The stronger the updraft is, the larger the stones that can be held up in the updraft with falling to the ground. Severe thunderstorms in Mississippi usually produce hailstones one inch in diameter or smaller. A few of the storms produce golfball to baseball size hailstones which cause substantial damage. The most severe thunderstorms across the country have been known to produce up to grapefruit size hailstones.

The potential for deaths,injuries, and damage from severe thunderstorms makes it imperative that our preparedness plans include thunderstorm safety and that we heed Severe Thunderstorm Warnings.

Just like Tornado Watches or Tornado Warnings, watches and warnings are issued for areas threatened by severe thunderstorms.

SEVERE THUNDERSTORM WATCH: Conditions are favorable for severe thunderstorms to develop in or close to the watch area. Be ready to seek shelter if a storm approaches or a warning is issued for your area.

SEVERE THUNDERSTORM WARNING: A Severe Thunderstorm is indicated by radar, or reported by a reliable source. Move to a safe place immediately and stay away from windows.

Lightning...A Killer

Lightning results from the buildup and discharge of electrical energy between positive and negative charges. Most lightning occurs within the cloud or between the cloud and the ground. Near a lightning strike, the air is heated to 50,000 degrees F, hotter than the surface of the sun! The rapid heating and cooling of air near the lightning channel causes a shock wave which results in thunder.

Lightning is often called the "The Underated Killer", since during an average year, more people die from lightning nationwide than caused by all the hurricanes and tornadoes combined. Lightning may strike people directly or it can start fires from which people may die.

Lightning will normally strike the highest object in the area of discharge and is especially attracted to metal, a good conductor of electricity. The highest object might be, for example, a tall tree, a boat on a lake, a tall antenna, or maybe a person standing in an open field. Lightning can strike several miles away from a thunderstorm. The danger lightning poses may exist even if it is not raining outside.

Lightning Safety Rules
• If you are outside, get inside a building or inside an all-metal(not convertible) vehicle.
• Inside a home, dont use telephones or other electronic equipment except in emergencies.
• Do not stand beneath a tall isolated tree, or in an open area.
• Avoid projecting above the surrounding landscape, as on a hilltop, in an open field, on the beach, or fishing from a boat.
• Get away from open water...also avoid tractors and other farm equipment,bicycles,motocycles, and golf carts. Put down golf clubs.
• Stay away from wire fences,clothesline, metal pipes, rails, or other metallic paths which could carry lightning to you from some distance away.
• In a forest, seek shelter in a low area under a thick growth of small trees. In open areas, go to a low place such as a ravine or valley. Be alert for flash floods.
• If you are isolated on a level field and you feel your hair stand on end, this indicates that lightning is about to strike. Drop to your knees and bend forward putting your hands on your knees. Do not lie flat on the ground.

Thunderstorm and Lightning Facts

The Facts:
• Thunderstorms are a common spring and summer occurence throughout Mississippi. Many Mississippians may not realize that thunderstorm winds and lightning kill more people each year than tornadoes.
• All thunderstorms produce lightning. Lightning often strikes outside of heavy rain and may occur as far as 10 miles away from any rainfall.
• Most lightning occurs within the cloud or between the cloud and ground.
• Lightning results from the buildup and discharge of electrical energy between positively and negatively charged areas. The action of rising and descending air within a thunderstorm separates positive and negative charges.
• The typical thunderstorm is 15 miles in diameter and lasts 30 minutes.
• Nearly 1,800 thunderstorms are occuring at any moment around the world. That is 16 million a year.
• Of the estimated 100,000 thunderstorms that occur each year in the United States, only about 10 percent are classified as being severe.
• Severe thunderstorms can produce damaging winds as strong as the winds in a weak tornado and can be life threatening.
• A Severe Thunderstorm can produce hail that is 3/4-inch in diameter or larger, winds 58 mph or higher, or tornadoes.
• Large hail causes nearly 1$ billion in damage to property and crops annually.
• The costliest US hailstorm occurred in Denver on July 11, 1990, and produced total hail damage estimate of $625 million.
• From 1997-1999, severe thunderstorms in Mississippi were responsible for 4 deaths and 56 injuries.
• In the past three years, lightning has killed a total of one person and injured three others in Mississippi, as reported to the National Weather Service.

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