This story does not necessarily represent the position of our parent company, IBM. Daily 14 Today. Thunderstorm Safety and Preparedness. By Brian Donegan April 23, At a Glance An estimated 16 million thunderstorms occur on Earth every year.
There are four main types of thunderstorms. Thunderstorms can occur year-round and at all hours. But they are most likely to happen in the spring and summer months and during the afternoon and evening hours.
How many thunderstorms are there every day? It is estimated that there are around 1, thunderstorms that occur across our planet every day. Are thunderstorms dangerous?
Yes, despite their small size, all thunderstorms are dangerous. Every thunderstorm produces lightning, which kills more people each year than tornadoes. What is lightning? Lightning is a bright flash of electricity produced by a thunderstorm. All thunderstorms produce lightning and are very dangerous. If you hear the sound of thunder, then you are in danger from lightning. Lightning kills and injures more people each year than hurricanes or tornadoes; between 75 to people.
What causes lightning? Lightning is an electric current. Within a thundercloud way up in the sky, many small bits of ice frozen raindrops bump into each other as they move around in the air. All of those collisions create an electric charge. After a while, the whole cloud fills up with electrical charges. The positive charges or protons form at the top of the cloud and the negative charges or electrons form at the bottom of the cloud.
Since opposites attract, that causes a positive charge to build up on the ground beneath the cloud. The grounds electrical charge concentrates around anything that sticks up, such as mountains, people, or single trees.
The charge coming up from these points eventually connects with a charge reaching down from the clouds and - zap - lightning strikes! Have you ever rubbed your feet across carpet and then touched a metal door handle?
If so, then you know that you can get shocked! Lightning works in the same way. Click Here to see where lightning is currently striking across the U. What causes thunder? Thunder is caused by lightning. It counts severe convective storms that may include tornadoes and other perils such as straight-line winds derechos and hail. The August 10, , Midwest Derecho, which is included in the chart as part of the August , outbreak, would rank as the fourth-costliest insured severe convective storm event on record for the U.
Includes events that occurred through Consumer Price Index. View Archived Tables The costliest U. View Archived Tables U. Tornado Count, Source: U. View Archived Graphs Back to top. Tornadoes A tornado is a violently rotating column of air that extends from a thunderstorm and comes into contact with the ground, according to the National Oceanic and Atmospheric Administration NOAA.
The National Weather Service considers a thunderstorm severe if it produces hail at least three-quarters of an inch in diameter, winds of 58 mph or stronger, or a tornado.
From to , a total of , severe thunderstorms were recorded not associated with tornadoes , an average of 19, annually. The frequency with which these giant generators of local weather occur, along with the quantity of energy they release and the variety of forms this energy can take, make thunderstorms great destroyers of life and property. Thunderstorms are generated by thermal instability in the atmosphere, and represent a violent example of convection—the vertical circulation produced in a fluid made thermally unstable by the local addition or subtraction of heat and the conversion of potential to kinetic energy.
The convective overturning of atmospheric layers that sets up a thunderstorm is dynamically similar to convective circulations observed under laboratory conditions, where distinct patterns are generated in liquids by unequal heating.
The orderly circulations produced in a laboratory are rarely encountered in the atmosphere, where areas corresponding to the rising core of laboratory convective cells are marked by cumulus and cumulonimbus clouds. Clouds are parcels of air that have been lifted high enough to condense the water vapor they contain into very small, visible particles. These particles are too small and light to fall out as rain. As the lifting process continues, these particles grow in size by collision and coalescence until they are large enough to fall against the updrafts associated with any developing convective clouds.
Cumulus for accumulation clouds begin their towering movement in response to atmospheric instability and convective overturning. Warmer and lighter than the surrounding air, they rise rapidly around a strong, central updraft.
These elements grow vertically, appearing as rising mounds, domes, or towers. The atmospheric instability in which thunderstorms begin may develop in several ways. Radiational cooling of cloud tops, heating of the cloud base from the ground, and frontal effects may produce an unstable condition. This is compensated in air, as in most fluids, by the convective overturning of layers to put denser layers below less-dense layers. Listed below are the rainiest cities in the U.
Average number of days with rain is shown parenthetically. Listed below are the U. The average number of days with rain is shown parenthetically. Mechanical processes are also at work. Warm, buoyant air may be forced upward by the wedge-like undercutting of a cold air mass, or lifted by a mountain slope. It is estimated that lightning flashes occur somewhere on Earth about times each second. Photo by C. Where these processes are sustained, and where lifting and cooling of the moist air continues, minor turbulence may generate a cumulus cloud, and then a towering cumulonimbus system.
The pattern of the vertical air movement in the center of the cumulus or cumulonimbus cloud system mimics the behavior of each convective cell. Most thunderstorms have, at maturity, a series of several cells, each following a life cycle characterized by changes in wind direction, development of precipitation and electrical charge, and other factors. In the first stage of thunderstorm development, an updraft drives warm air up beyond condensation levels, where clouds form, and where continued upward movement produces cumulus formations.
The updraft develops in a region of gently converging surface winds in which the atmospheric pressure is slightly lower than in surrounding areas. As the updraft continues, air flows in through the cloud's sides in a process called entrainment, mixing with and feeding the updraft. The updraft may be further augmented by a chimney effect produced by winds at high altitude.
A developing thunderstorm also feeds on another source of energy. Once the cloud has formed, the phase changes of water result in a release of heat energy, which increases the momentum of the storm's vertical development. The rate at which this energy is released is directly related to the amount of gaseous water vapor converted to liquid water.
As water vapor in the burgeoning cloud is raised to saturation levels, the air is cooled sufficiently to liberate solid and liquid particles of water, and rain and snow begin to fall within the cloud.
The cloud tower rises above 1. The formation and precipitation of particles large enough and in sufficient quantity to fall against the updraft marks the beginning of the second, mature stage of a thunderstorm cell. A thunderstorm's mature stage is marked by a transition in wind direction within the storm cells. The prevailing updraft, which initiated the cloud's growth, is joined by a downdraft generated by precipitation.
The downdraft is fed and strengthened, as the updraft was, by the addition of entrained. Drawing by Argosy. The mature storm dominates the electrical field and atmospheric circulation for several miles around. Lightning—the discharge of electricity between large charges of opposite signs—occurs soon after precipitation begins, a clue to the relationship of thunderstorm electrification and formation of ice crystals and raindrops.
At maturity, a thunderstorm cloud is several miles across its base and may tower to altitudes of 40, ft or more. The swift winds of the upper troposphere shred the cloud top into the familiar anvil form, visible in dry regions as lonely giants, or as part of a squall line. On the ground directly beneath a storm system, the mature stage is initially felt as rain, which is soon joined by the strong downdraft. The downdraft spreads out from the cloud in gusting, divergent winds, and brings a marked drop in temperature.
Even where the rain has not reached the ground, this cold air stream flowing over the surface can identify a thunderstorm's mature stage. This is nature's warning that a thunderstorm is in its most violent phase. It is in this phase that a thunderstorm unleashes its lightning, hail, heavy rain, high wind, and—most destructive of all— its tornado. But even as it enters maturity, the storm has begun. The violent downdraft initially shares the circulation with the sustaining updraft, but then strangles it.
As the updraft is cut off from its converging low-level winds, the storm loses its source of moisture and heat energy. Precipitation weakens and stops, and the cold downdraft ceases. And the thunderstorm, violent creature of an instant, spreads and dies. Storms, based on their physical characteristics, can be classified into four basic categories: single cell, multicell cluster, multicell line, and supercell.
Though single-cell storms are rare and relatively weak, they can produce brief bouts of severe weather lasting 20—30 minutes; these storms are not well organized and are seemingly random in occurrence.
In the unstable single-cell environment, oftentimes pulse severe storms form. Single-cell storms are difficult to forecast. Like a single-cell storm, each cell of a multicell cluster storm lasts usually only about 20 minutes; however, the cluster itself can last for several hours. The multicell cluster, the most common type of thunderstorm, comprises a number. The most mature cells are found at the center of the cluster, new cells form at the upwind usually the west or southwest edge, while the dissipating cells are found at the downwind usually east or northeast edge.
Multicell clusters are stronger than single-cell storms, and produce heavy rainfall, down-bursts wind speeds reaching 80 mph , medium-sized hail, and periodic tornadoes. A long line of storms with a leading edge of strong wind gusts is called a multicell line storm, or squall line.
Moving forward, the wind gusts of cold air force unstable warm air into the updraft at the stormfront's edge; heavy rain and large hail immediately follow. A large area behind this produces lighter rain. Squall lines produce golf-ball-size hail, heavy rains, tornadoes, and most notably, weak to strong downbursts.
The most severe and rare type of thunderstorm is the supercell. It is a highly organized storm consisting of one main updraft that can reach — mph. This rotating updraft is called a mesocyclone and works to produce extremely large hail 2 in , major downbursts 80 mph , and fierce tornadoes. Microbursts are small-scale, hard-hitting downdrafts that result in both vertical and horizontal wind shears that can be extremely hazardous to low-altitude aircraft.
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