A storm is any disturbed state of an environment or in an astronomical body's atmosphere especially affecting its surface, and strongly implying severe weather. It may be marked by significant disruptions to normal conditions such as strong wind, tornadoes, hail, thunder and lightning (a thunderstorm), heavy precipitation (snowstorm, rainstorm), heavy freezing rain (ice storm), strong winds (tropical cyclone, windstorm), or wind transporting some substance through the atmosphere as in a dust storm, blizzard, sandstorm, etc.
Storms have the potential to harm lives and property via storm surge, heavy rain or snow causing flooding or road impassibility, lightning, wildfires, and vertical wind shear. Systems with significant rainfall and duration help alleviate drought in places they move through. Heavy snowfall can allow special recreational activities to take place which would not be possible otherwise, such as skiing and snowmobiling.
storms are often accompanied by violent winds, and pass rapidly.
The English word comes from Proto-Germanic *sturmaz meaning "noise, tumult".
Storms are created when a center of low pressure develops with the system of high pressure surrounding it. This combination of opposing forces can create winds and result in the formation of storm clouds such as cumulonimbus. Small localized areas of low pressure can form from hot air rising off hot ground, resulting in smaller disturbances such as dust devils and whirlwinds.
There are many varieties and names for storms:
- Blizzard – There are varying definitions for blizzards, both over time and by location. In general, a blizzard is accompanied by gale-force winds, heavy snow (accumulating at a rate of at least 5 centimeters (2 in) per hour), and very cold conditions (below approximately −10 degrees Celsius or 14 F). Lately, the temperature criterion has fallen out of the definition across the United States
- Bomb cyclone – A rapid deepening of a mid-latitude cyclonic low-pressure area, typically occurring over the ocean, but can occur over land. The winds experienced during these storms can be as powerful as that of a typhoon or hurricane.
- Coastal Storm – Large wind waves and/or storm surge that strike the coastal zone. Their impacts include coastal erosion and coastal flooding
- Derecho – A derecho is a widespread, long-lived, straight-line wind storm that is associated with a land-based, fast-moving group of severe thunderstorms.
- Dust devil – A small, localized updraft of rising air.
- Dust storm – A situation in which winds pick up large quantities of sand or soil, greatly reducing the visibility
- Firestorm – Firestorms are conflagrations which attain such intensity that they create and sustain their own wind systems. It is most commonly a natural phenomenon, created during some of the largest bushfires, forest fires, and wildfires. The Peshtigo Fire is one example of a firestorm. Firestorms can also be deliberate effects of targeted explosives such as occurred as a result of the aerial bombings of Dresden. Nuclear detonations generate firestorms if high winds are not present.
- Gale – An with sustained winds between 34–48 knots (39–55 mph or 63–90 km/h).
- Hailstorm – A type of storm that precipitates round chunks of ice. Hailstorms usually occur during regular thunderstorms. While most of the hail that precipitates from the clouds is fairly small and virtually harmless, there are occasional occurrences of hail greater than 2 inches (5 cm) in diameter that can cause much damage and injuries.
- Hypercane – A hypothetical tropical cyclone that could potentially form over 50 °C (122 °F) water. Such a storm would produce winds of over 800 km/h (500 mph). A series of hypercanes may have formed during the asteroid or comet impact that killed the non-avian dinosaurs 66 million years ago. Such a phenomenon could also occur during a supervolcanic eruption, or extreme global warming.
- Ice storm – Ice storms are one of the most dangerous forms of winter storms. When surface temperatures are below freezing, but a thick layer of above-freezing air remains aloft, rain can fall into the freezing layer and freeze upon impact into a glaze of ice. In general, 8 millimetres (0.31 in) of accumulation is all that is required, especially in combination with breezy conditions, to start downing power lines as well as tree limbs. Ice storms also make unheated road surfaces too slick to drive upon. Ice storms can vary in time range from hours to days and can cripple small towns and large metropolitan cities alike.
- Microburst – A very powerful windstorm produced during a thunderstorm that only lasts a few minutes.
- Ocean Storm or sea storm – Storm conditions out at sea are defined as having sustained winds of 48 knots (55 mph or 90 km/h) or greater. Usually just referred to as a storm, these systems can sink vessels of all types and sizes.
- Snowstorm – A heavy fall of snow accumulating at a rate of more than 5 centimeters (2 in) per hour that lasts several hours. Snow storms, especially ones with a high liquid equivalent and breezy conditions, can down tree limbs, cut off power connections and paralyze travel over large regions.
- Squall – Sudden onset of wind increase of at least 16 knots (30 km/h) or greater sustained for at least one minute.
- Thunderstorm – A thunderstorm is a type of storm that generates both lightning and thunder. It is normally accompanied by heavy precipitation. Thunderstorms occur throughout the world, with the highest frequency in tropical rainforest regions where there are conditions of high humidity and temperature along with atmospheric instability. These storms occur when high levels of condensation form in a volume of unstable air that generates deep, rapid, upward motion in the atmosphere. The heat energy creates powerful rising air currents that swirl upwards to the tropopause. Cool descending air currents produce strong downdraughts below the storm. After the storm has spent its energy, the rising currents die away and downdraughts break up the cloud. Individual storm clouds can measure 2–10 km across.
- Tornado – A tornado is a violent, destructive whirlwind storm occurring on land. Usually its appearance is that of a dark, funnel-shaped cloud. Often tornadoes are preceded by or associated with thunderstorms and a wall cloud. They are often called the most destructive of storms, and while they form all over the planet, the interior of the United States is the most prone area, especially throughout Tornado Alley.
- Tropical cyclone – A tropical cyclone is a storm system with a closed circulation around a centre of low pressure, fueled by the heat released when moist air rises and condenses. The name underscores its origin in the tropics and their cyclonic nature. Tropical cyclones are distinguished from other cyclonic storms such as nor'easters and polar lows by the heat mechanism that fuels them, which makes them "warm core" storm systems. Tropical cyclones form in the oceans if the conditions in the area are favorable, and depending on their strength and location, there are various terms by which they are called, such as tropical depression, tropical storm, hurricane and typhoon.
- Wind storm – A storm marked by high wind with little or no precipitation. Windstorm damage often opens the door for massive amounts of water and debris to cause further damage to a structure. European windstorms and derechos are two type of windstorms. High wind is also the cause of sandstorms in dry climates.