Thunderstorms & Lightning

Thunderstorms affect relatively small areas when compared with hurricanes and winter storms. 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. That's 16 million a year! Despite their small size all thunderstorms can be dangerous. Every thunderstorm produces lightning that kills more people each year than tornadoes. Other associated dangers of thunderstorms include tornadoes, strong winds, hail and flooding.

Tornadoes

Nature's most violent storms.
Winds can exceed 200 mph. Result in an average of 80 deaths and 1,500 injuries each year.
Refer to the Tornado Section and "Tornado Safety Checklist." (Checklist 8 in Appendix).

Straight-line Winds are responsible for most thunderstorm wind damage. A small area of rapidly descending air beneath a thunderstorm can cause damaging winds in excess of 100 mph. The strong winds usually approach from one direction and may be known as "straight-line" winds. One type of straight-line winds, the downburst, can cause as much damage as a strong tornado. For mitigation options, download the brochure, "Protecting your Commercial Building from Wind Damage" on the Florida business Disaster Survival Kit or log onto www.ibhs.org.

Hail

Hail is precipitation in the form of balls or irregular lumps of ice which is always produced by convective clouds. The type of convective cloud is nearly always cumulonimbus, or more commonly, a thundercloud.individual unit of hail is called a hailstone. Usually a hailstone begins as a frozen raindrop or snow pellet within a thunderstorm. The turbulent updrafts and downdrafts within the cloud send the hailstones up and down several times, where they gather layer upon layer of ice.
When the ice becomes too heavy to be supported by the updraft it falls to the ground.
A hailstone ranges in size from that of a pea to that of a grapefruit, or from about 1/5 inch to more than 5 inches in diameter.

Lightning

The ingredient that defines a thunderstorm is lightning.

It occurs with all thunderstorms.
It averages 93 deaths and 300 injuries annually in the U.S.
It causes several hundred million dollars in damage.
Florida leads the nation in number of lightning deaths and injuries.
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.
The average flash could light a 100-watt light bulb for more than 3 months. Most lightning occurs within the cloud or between the cloud and ground.
The air in a lightning bolt is 50,000 F° - five times hotter than the surface of the sun!! The rapid heating of air in the lightning channel causes a shock wave that results in thunder.
The potentials for fire and power outage are the primary concern

Lightning Myths & Facts

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. Contact your local American Red Cross Chapter for information on CPR and first aid classes.

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.

What to Do Before Thunderstorms Approach

Know the terms used by weather forecasters:

Severe Thunderstorm Watch - Tells you when and where severe thunderstorms are likely to occur. Watch the sky and stay tuned to radio or television to know when warnings are issued.
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.

Know thunderstorm facts:

Thunderstorms may occur singly, in clusters, or in lines.
Some of the most severe weather occurs when a single thunderstorm affects one location for an extended time.
Thunderstorms typically produce heavy rain for a brief period, anywhere from 30 minutes to an hour.
Warm, humid conditions are very favorable for thunderstorm development.
A typical thunderstorm is 15 miles in diameter and lasts an average of 30 minutes.
Of the estimated 100,000 thunderstorms each year in the United States, about 10 percent are classified as severe.
A thunderstorm is classified as severe if it produces hail at least three-quarters of an inch in diameter, has winds of 58 miles per hour or higher, or produces a tornado.

Know the calculation to determine how close you are to a thunderstorm:

Count the number of seconds between a flash of lightning and the next clap of thunder. Divide this number by 5 to determine the distance to the lightning in miles.

Remove dead or rotting trees and branches that could fall and cause injury or damage during a severe thunderstorm.
When a thunderstorm approaches, secure outdoor objects that could blow away or cause damage. Shutter windows, if possible, and secure outside doors. If shutters are not available, close window blinds, shades or curtains.

For more information, refer to the Lightning Safety Checklist (Checklist 9 in Appendix) in the Guidebook or on the checklists page of this site.