Thunderstorms are storms that involve lightning, thunder, rains, winds and, in some cases, hail. If you take precautions, thunderstorms are not as dangerous as cyclones and earthquakes, but if you do not take safety precautions thunderstorms can be life-threatening.
A thunderstorm, also known as an electrical storm or a lightning storm, is a storm characterized by the presence of lightning and its acoustic effect on the Earth’s atmosphere, known as thunder. Relatively weak thunderstorms are sometimes called thundershowers. Thunderstorms occur in a type of cloud known as a cumulonimbus. They are usually accompanied by strong winds, and often produce heavy rain and sometimes snow, sleet, or hail, but some thunderstorms produce little precipitation or no precipitation at all. Thunderstorms may line up in a series or become a rainband, known as a squall line. Strong or severe thunderstorms include some of the most dangerous weather phenomena, including large hail, strong winds, and tornadoes. Some of the most persistent severe thunderstorms, known as supercells, rotate as do cyclones. While most thunderstorms move with the mean wind flow through the layer of the troposphere that they occupy, vertical wind shear sometimes causes a deviation in their course at a right angle to the wind shear direction.
Thunderstorms result from the rapid upward movement of warm, moist air, sometimes along a front. As the warm, moist air moves upward, it cools, condenses, and forms a cumulonimbus cloud that can reach heights of over 20 kilometres (12 mi). As the rising air reaches its dew point temperature, water vapor condenses into water droplets or ice, reducing pressure locally within the thunderstorm cell. Any precipitation falls the long distance through the clouds towards the Earth’s surface. As the droplets fall, they collide with other droplets and become larger. The falling droplets create a downdraft as it pulls cold air with it, and this cold air spreads out at the Earth’s surface, occasionally causing strong winds that are commonly associated with thunderstorms.
Thunderstorms can form and develop in any geographic location but most frequently within the mid-latitude, where warm, moist air from tropical latitudes collides with cooler air from polar latitudes. Thunderstorms are responsible for the development and formation of many severe weather phenomena. Thunderstorms, and the phenomena that occur along with them, pose great hazards. Damage that results from thunderstorms is mainly inflicted by downburst winds, large hailstones, and flash flooding caused by heavy precipitation. Stronger thunderstorm cells are capable of producing tornadoes and waterspouts.
There are four types of thunderstorms: single-cell, multi-cell cluster, multi-cell lines and supercells. Supercell thunderstorms are the strongest and most severe. Mesoscale convective systems formed by favorable vertical wind shear within the tropics and subtropics can be responsible for the development of hurricanes. Dry thunderstorms, with no precipitation, can cause the outbreak of wildfires from the heat generated from the cloud-to-ground lightning that accompanies them. Several means are used to study thunderstorms: weather radar, weather stations, and video photography. Past civilizations held various myths concerning thunderstorms and their development as late as the 18th century. Beyond the Earth’s atmosphere, thunderstorms have also been observed on the planets of Jupiter, Saturn, Neptune, and, probably, Venus.
Mythology and religion
Thunderstorms strongly influenced many early civilizations. Greeks believed that they were battles waged by Zeus, who hurled lightning bolts forged by Hephaestus. Some American Indian tribes associated thunderstorms with the Thunderbird, who they believed was a servant of the Great Spirit. The Norse considered thunderstorms to occur when Thor went to fight Jötnar, with the thunder and lightning being the effect of his strikes with the hammer Mjölnir. Hinduism recognizes Indra as the god of rain and thunderstorms. Christian doctrine accepts that fierce storms are the work of God. These ideas were still within the mainstream as late as the 18th century.
Martin Luther was out walking when a thunderstorm began, causing him to pray to God for being saved and promising to become a monk.
In more contemporary times, thunderstorms have taken on the role of a scientific curiosity. Every spring, storm chasers head to the Great Plains of the United States and the Canadian Prairies to explore the scientific aspects of storms and tornadoes through use of videotaping. Radio pulses produced by cosmic rays are being used to study how electric charges develop within thunderstorms. More organized meteorological projects such as VORTEX2 use an array of sensors, such as the Doppler on Wheels, vehicles with mounted automated weather stations, weather balloons, and unmanned aircraft to investigate thunderstorms expected to produce severe weather. Lightning is detected remotely using sensors that detect cloud-to-ground lightning strokes with 95 percent accuracy in detection and within 250 metres (820 ft) of their point of origin.
Thunderstorms result from rapid upward movement of warm, moist air, which form very high (even more than 20 km) cumulonimbus clouds. They are common in tropical regions during the rainy season, but can occur around the globe depending on the season of the respective regions. If you see a towering cauliflower-like cloud in the distance, it is an imminent sign of a thunderstorm brewing or currently occurring (from nearby, the shape is masked).
Lightning tends to hit the highest object towering from the ground, so avoid hill tops and open areas and do not seek shelter under a high or lone tree. Get indoors if possible or crouch down on the ground if there’s no shelter. Cars with enough steel (many modern ones are mostly plastic) form Faraday cages and are thus safe, but avoid driving if possible. Avoid anything connected to power lines, phone lines etc., as electricity induced by a lightning strike can travel far along these. Swimming or taking a shower is dangerous for the same reason.
During a storm, unplug your electronic devices to avoid risk of having them fried by a lightning-induced power surge. If you plan to spend a lot of time in a high-risk area, get a surge protector. These are reasonably cheap devices that go between your computer or other valuable device and the wall socket; they do not give perfect protection, but they do greatly reduce risk.
In a semi-open area the safest position is at a distance about half the height from a tree or other high object – if the lightning strikes here, it will hit that object instead of you; the strong sound, electricity spread in the ground and pieces flying from the hit object are still dangerous. Parts of the lightning can even bounce off to people in the vicinity. Keep your feet together so that electricity in the ground does not travel between them through you. Spread out, so that if somebody gets hurt, the others are unharmed and ready to help.
Each year, many people are killed or seriously injured by severe thunderstorms despite the advance warning. While severe thunderstorms are most common in the spring and summer, they can occur at just about any time of the year.
Cloud-to-ground lightning frequently occurs within the phenomena of thunderstorms and have numerous hazards towards landscapes and populations. One of the more significant hazards lightning can pose is the wildfires they are capable of igniting. Under a regime of low precipitation (LP) thunderstorms, where little precipitation is present, rainfall cannot prevent fires from starting when vegetation is dry as lightning produces a concentrated amount of extreme heat. Direct damage caused by lightning strikes occurs on occasion. In areas with a high frequency for cloud-to-ground lightning, like Florida, lightning causes several fatalities per year, most commonly to people working outside.
Acid rain is also a frequent risk produced by lightning. Distilled water has a neutral pH of 7. “Clean” or unpolluted rain has a slightly acidic pH of about 5.2, because carbon dioxide and water in the air react together to form carbonic acid, a weak acid (pH 5.6 in distilled water), but unpolluted rain also contains other chemicals. Nitric oxide present during thunderstorm phenomena, caused by the oxidation of atmospheric nitrogen, can result in the production of acid rain, if nitric oxide forms compounds with the water molecules in precipitation, thus creating acid rain. Acid rain can damage infrastructures containing calcite or certain other solid chemical compounds. In ecosystems, acid rain can dissolve plant tissues of vegetations and increase acidification process in bodies of water and in soil, resulting in deaths of marine and terrestrial organisms.
Hail is the falling of solid balls of ice during a thunderstorm. Hailstorms are not very common but are a risk in some areas such as the Canadian Prairies and some regions of Australia. In mid-latitudes and tropical regions, they typically occur in spring or transition from wet to dry season.
Any thunderstorm that produces hail that reaches the ground is known as a hailstorm. Thunderclouds that are capable of producing hailstones are often seen obtaining green coloration. Hail is more common along mountain ranges because mountains force horizontal winds upwards (known as orographic lifting), thereby intensifying the updrafts within thunderstorms and making hail more likely. One of the more common regions for large hail is across mountainous northern India, which reported one of the highest hail-related death tolls on record in 1888. China also experiences significant hailstorms. Across Europe, Croatia experiences frequent occurrences of hail.
In North America, hail is most common in the area where Colorado, Nebraska, and Wyoming meet, known as “Hail Alley”. Hail in this region occurs between the months of March and October during the afternoon and evening hours, with the bulk of the occurrences from May through September. Cheyenne, Wyoming is North America’s most hail-prone city with an average of nine to ten hailstorms per season. In South America, areas prone to hail are cities like Bogotá, Colombia.
Hail can cause serious damage, notably to automobiles, aircraft, skylights, glass-roofed structures, livestock, and most commonly, farmers’ crops. Hail is one of the most significant thunderstorm hazards to aircraft. When hail stones exceed 13 millimetres (0.5 in) in diameter, planes can be seriously damaged within seconds. The hailstones accumulating on the ground can also be hazardous to landing aircraft. Wheat, corn, soybeans, and tobacco are the most sensitive crops to hail damage. Hail is one of Canada’s most costly hazards. Hailstorms have been the cause of costly and deadly events throughout history. One of the earliest recorded incidents occurred around the 9th century in Roopkund, Uttarakhand, India. The largest hailstone in terms of maximum circumference and length ever recorded in the United States fell in 2003 in Aurora, Nebraska, United States.
In most storms, the hailstones are about the size of a pea; being bombarded with these can be quite unpleasant but is not really dangerous. Some storms have larger stones, golf ball-size or more, and these are definitely dangerous; they can shatter a car’s windshield or knock a person unconscious!
If there is a threat of hail, bring all people, pets, and your car to an indoor space (your house or a garage) to avoid harm and hurt, and get away from windows or openings when hail hits.
Tornadoes and waterspouts
A tornado is a violent, rotating column of air in contact with both the surface of the earth and a cumulonimbus cloud (otherwise known as a thundercloud) or, in rare cases, the base of a cumulus cloud. Tornadoes come in many sizes but are typically in the form of a visible condensation funnel, whose narrow end touches the earth and is often encircled by a cloud of debris and dust. Most tornadoes have wind speeds between 40 and 110 mph (64 and 177 km/h), are approximately 75 metres (246 ft) across, and travel several kilometers (a few miles) before dissipating. Some attain wind speeds of more than 300 mph (480 km/h), stretch more than 1,600 metres (1 mi) across, and stay on the ground for more than 100 kilometres (dozens of miles).
In a few parts of the world, especially in the United States, thunderstorms can also spawn tornadoes, spinning columns of air that sucks everything it blows inward and upward. They can have winds up to hurricane-force speeds (more than 100mph/160kph) and travel along a swath of area. These typically lasts up to an hour at most, but often comes with little warning especially for those unaware. They have been known to down trees and power lines, and even hoist a house from its foundation!
Tornado typically occurs in spring especially in mid-latitude countries. Large and organized weather systems that span across multiple states can spawn a tornado outbreak; which are multiple tornadoes forming within a wide area.
Spotting a tornado is easy at daytime but dangerously difficult at night. If you see a funnel coming down from a dark cloud or debris & dirt flying high, it is a good sign that a tornado is about to happen at that very spot. Hail, especially of larger size, usually precedes a brewing tornado. If you can’t spot any of them at night, watch the weather forecast on TV or listen on the radio. In some localities, sirens warn of an incoming tornado in the immediate area from which you must seek shelter immediately. Fleeing a tornado by motorcar can be tough because heavy rains may blind drivers from seeing a tornado and its direction of travel.
The Fujita scale and the Enhanced Fujita Scale rate tornadoes by damage caused. An EF0 tornado, the weakest category, damages trees but not substantial structures. An EF5 tornado, the strongest category, rips buildings off their foundations and can deform large skyscrapers. The similar TORRO scale ranges from a T0 for extremely weak tornadoes to T11 for the most powerful known tornadoes. Doppler radar data, photogrammetry, and ground swirl patterns (cycloidal marks) may also be analyzed to determine intensity and award a rating.
Waterspouts have similar characteristics as tornadoes, characterized by a spiraling funnel-shaped wind current that form over bodies of water, connecting to large cumulonimbus clouds. Waterspouts are generally classified as forms of tornadoes, or more specifically, non-supercelled tornadoes that develop over large bodies of water. These spiralling columns of air frequently develop within tropical areas close to the equator, but are less common within areas of high latitude.
Flash flooding is the process where a landscape, most notably an urban environment, is subjected to rapid floods. These rapid floods occur more quickly and are more localized than seasonal river flooding or areal flooding and are frequently (though not always) associated with intense rainfall. Flash flooding can frequently occur in slow-moving thunderstorms and is usually caused by the heavy liquid precipitation that accompanies it. Flash floods are most common in densely populated urban environments, where few plants and bodies of water are present to absorb and contain the extra water. Flash flooding can be hazardous to small infrastructure, such as bridges, and weakly constructed buildings. Plants and crops in agricultural areas can be destroyed and devastated by the force of raging water. Automobiles parked within affected areas can also be displaced. Soil erosion can occur as well, exposing risks of landslide phenomena.
Downburst winds can produce numerous hazards to landscapes experiencing thunderstorms. Downburst winds are generally very powerful, and are often mistaken for wind speeds produced by tornadoes, due to the concentrated amount of force exerted by their straight-horizontal characteristic. Downburst winds can be hazardous to unstable, incomplete, or weakly constructed infrastructures and buildings. Agricultural crops, and other plants in nearby environments can be uprooted and damaged. Aircraft engaged in takeoff or landing can crash. Automobiles can be displaced by the force exerted by downburst winds. Downburst winds are usually formed in areas when high pressure air systems of downdrafts begin to sink and displace the air masses below it, due to their higher density. When these downdrafts reach the surface, they spread out and turn into the destructive straight-horizontal winds.
Thunderstorm asthma is the triggering of an asthma attack by environmental conditions directly caused by a local thunderstorm. During a thunderstorm, pollen grains can absorb moisture and then burst into much smaller fragments with these fragments being easily dispersed by wind. While larger pollen grains are usually filtered by hairs in the nose, the smaller pollen fragments are able to pass through and enter the lungs, triggering the asthma attack.
Most thunderstorms come and go fairly uneventfully; however, any thunderstorm can become severe, and all thunderstorms, by definition, present the danger of lightning. Thunderstorm preparedness and safety refers to taking steps before, during, and after a thunderstorm to minimize injury and damage.
Preparedness refers to precautions that should be taken before a thunderstorm. Some preparedness takes the form of general readiness (as a thunderstorm can occur at any time of the day or year). Preparing a family emergency plan, for example, can save valuable time if a storm arises quickly and unexpectedly. Preparing the home by removing dead or rotting limbs and trees, which can be blown over in high winds, can also significantly reduce the risk of property damage and personal injury.
The National Weather Service (NWS) in the United States recommends several precautions that people should take if thunderstorms are likely to occur:
Know the names of local counties, cities, and towns, as these are how warnings are described.
Monitor forecasts and weather conditions and know whether thunderstorms are likely in the area.
Be alert for natural signs of an approaching storm.
Cancel or reschedule outdoor events (to avoid being caught outdoors when a storm hits).
Take action early so you have time to get to a safe place.
Get inside a substantial building or hard-topped metal vehicle before threatening weather arrives.
If you hear thunder, get to the safe place immediately.
Avoid open areas like hilltops, fields, and beaches, and don’t be or be near the tallest objects in an area when thunderstorms are occurring.
Don’t shelter under tall or isolated trees during thunderstorms.
If in the woods, put as much distance as possible between you and any trees during thunderstorms.
If in a group, spread out to increase the chances of survivors who could come to the aid of any victims from a lightning strike.
While safety and preparedness often overlap, “thunderstorm safety” generally refers to what people should do during and after a storm. The American Red Cross recommends that people follow these precautions if a storm is imminent or in progress:
Take action immediately upon hearing thunder. Anyone close enough to the storm to hear thunder can be struck by lightning.
Avoid electrical appliances, including corded telephones. Cordless and wireless telephones are safe to use during a thunderstorm.
Close and stay away from windows and doors, as glass can become a serious hazard in high wind.
Do not bathe or shower, as plumbing conducts electricity.
If driving, safely exit the roadway, turn on hazard lights, and park. Remain in the vehicle and avoid touching metal.
The NWS stopped recommending the “lightning crouch” in 2008 as it doesn’t provide a significant level of protection and will not significantly lower the risk of being killed or injured from a nearby lightning strike.