A thunderstorm is a local storm that produces lightning and thunder . It can consist of a single cumulonimbus cloud , a cluster of clouds, or a line of clouds. Thunderstorms form when moist, unstable air near the surface is lifted. This lifting can be caused by thermals generated from a strongly heated surface, the forcing of air upward along a frontal surface or terrain surfaces, or by the upward motion produced by winds converging near the surface. Thunderstorms are generally transient phenomena that last anywhere from 10 minutes to several hours. Thunderstorms are often accompanied by showery rain and gusty winds, and may also bring hail or snow. Thunderstorms occur most frequently during summer, but they are not unknown in the winter when thunder can sometimes be heard during intense snowstorms.
It is estimated that there are as many as 40,000 thunderstorm occurrences each day world-wide. This translates into an astounding 14.6 million occurrences annually! The United States certainly experiences its share of thunderstorm occurrences. North Carolina's annual thunderstorm days per year are 40 to 50.
This figure shows the average number of thunderstorm days each year throughout the U.S. The most frequency of occurrence is greatest in the southeastern states, with Florida having the highest incidence (80 to 100+ thunderstorm days per year). It is in this part of the country that warm, moist air from the Gulf of Mexico and Atlantic Ocean (which we will see later are necessary ingredients for thunderstorm development) is most readily available to fuel thunderstorm development.
- At any given moment, nearly 1,800 thunderstorms are in progress over the surface of the earth.
- On average, the United States gets 100,00 thunderstorms each year. Approximately 1,000 tornadoes develop from these storms.
- Large hail results in nearly $1 billion in damage to property and crops.
- The power of lightning's electrical charge and intense heat can electrocute on contact, split trees, ignite fires and cause electrical failures.
- More deaths from lightning occur on the East Coast. More forest fires are started in the West as the lightning season coincides with the dry season there.
- Approximately 10,000 forest fires are started each year by lightning.
- Approximately $100 million in annual losses result from forest and building fires caused by lightning.
- Straight-line winds exceeding 100 mph are responsible for most thunderstorm damage.