Severe weather phenomena are weather conditions that are hazardous to human life and property.
Weather is the state of the atmosphere, describing for example the degree to which it is hot or cold, wet or dry, calm or stormy, clear or cloudy. Most weather phenomena occur in the lowest level of the atmosphere, the troposphere, just below the stratosphere. Weather refers to day-to-day temperature and precipitation activity, whereas climate is the term for the averaging of atmospheric conditions over longer periods of time. When used without qualification, "weather" is generally understood to mean the weather of Earth.
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Severe weather can occur under a variety of situations, but three characteristics are generally needed: a temperature or moisture boundary, moisture, and (in the event of severe, precipitation-based events) instability in the atmosphere.
In meteorology, a cyclone is a large scale air mass that rotates around a strong center of low atmospheric pressure. Cyclones are characterized by inward spiraling winds that rotate about a zone of low pressure. The largest low-pressure systems are polar vortices and extratropical cyclones of the largest scale. Warm-core cyclones such as tropical cyclones and subtropical cyclones also lie within the synoptic scale. Mesocyclones, tornadoes and dust devils lie within smaller mesoscale. Upper level cyclones can exist without the presence of a surface low, and can pinch off from the base of the tropical upper tropospheric trough during the summer months in the Northern Hemisphere. Cyclones have also been seen on extraterrestrial planets, such as Mars and Neptune. Cyclogenesis is the process of cyclone formation and intensification. Extratropical cyclones begin as waves in large regions of enhanced mid-latitude temperature contrasts called baroclinic zones. These zones contract and form weather fronts as the cyclonic circulation closes and intensifies. Later in their life cycle, extratropical cyclones occlude as cold air masses undercut the warmer air and become cold core systems. A cyclone's track is guided over the course of its 2 to 6 day life cycle by the steering flow of the subtropical jet stream.
Fog is a visible aerosol consisting of tiny water droplets or ice crystals suspended in the air at or near the Earth's surface. Fog can be considered a type of low-lying cloud, usually resembling stratus, and is heavily influenced by nearby bodies of water, topography, and wind conditions. In turn, fog has affected many human activities, such as shipping, travel, and warfare.
A heat wave is a period of excessively hot weather, which may be accompanied by high humidity, especially in oceanic climate countries. While definitions vary, a heat wave is usually measured relative to the usual weather in the area and relative to normal temperatures for the season. Temperatures that people from a hotter climate consider normal can be termed a heat wave in a cooler area if they are outside the normal climate pattern for that area.
An avalanche is an event that occurs when a cohesive slab of snow lying upon a weaker layer of snow fractures and slides down a steep slope. Avalanches are typically triggered in a starting zone from a mechanical failure in the snowpack when the forces of the snow exceed its strength but sometimes only with gradual widening. After initiation, avalanches usually accelerate rapidly and grow in mass and volume as they entrain more snow. If the avalanche moves fast enough, some of the snow may mix with the air forming a powder snow avalanche, which is a type of gravity current.
A blizzard is a severe snowstorm characterized by strong sustained winds of at least 35 mph (56 km/h) and lasting for a prolonged period of time—typically three hours or more. A ground blizzard is a weather condition where snow is not falling but loose snow on the ground is lifted and blown by strong winds. Blizzards can have an immense size and usually stretch to hundreds or thousands of kilometres.
A drought or drouth is a natural disaster of below-average precipitation in a given region, resulting in prolonged shortages in the water supply, whether atmospheric, surface water or ground water. A drought can last for months or years, or may be declared after as few as 15 days. It can have a substantial impact on the ecosystem and agriculture of the affected region and harm to the local economy. Annual dry seasons in the tropics significantly increase the chances of a drought developing and subsequent bush fires. Periods of heat can significantly worsen drought conditions by hastening evaporation of water vapour.
Hail is a form of solid precipitation. It is distinct from ice pellets, though the two are often confused. It consists of balls or irregular lumps of ice, each of which is called a hailstone. Ice pellets fall generally in cold weather while hail growth is greatly inhibited during cold surface temperatures.
A tornado is a rapidly rotating column of air that is in contact with both the surface of the Earth and a cumulonimbus cloud or, in rare cases, the base of a cumulus cloud. The windstorm is often referred to as a twister, whirlwind or cyclone, although the word cyclone is used in meteorology to name a weather system with a low-pressure area in the center around which, from an observer looking down toward the surface of the earth, winds blow counterclockwise in the Northern Hemisphere and clockwise in the Southern. Tornadoes come in many shapes and sizes, and they are often visible in the form of a condensation funnel originating from the base of a cumulonimbus cloud, with a cloud of rotating debris and dust beneath it. Most tornadoes have wind speeds less than 110 miles per hour (180 km/h), are about 250 feet (80 m) across, and travel a few miles before dissipating. The most extreme tornadoes can attain wind speeds of more than 300 miles per hour (480 km/h), are more than two miles (3 km) in diameter, and stay on the ground for dozens of miles.
Lightning is a violent and sudden electrostatic discharge where two electrically charged regions in the atmosphere temporarily equalize themselves, usually during a thunderstorm.
Extreme weather includes unexpected, unusual, unpredictable, severe or unseasonal weather; weather at the extremes of the historical distribution—the range that has been seen in the past. Often, extreme events are based on a location’s recorded weather history and defined as lying in the most unusual ten percent. In recent years some extreme weather events have been attributed to human-induced global warming, with studies indicating an increasing threat from extreme weather in the future.
Meteorology is a branch of the atmospheric sciences which includes atmospheric chemistry and atmospheric physics, with a major focus on weather forecasting. The study of meteorology dates back millennia, though significant progress in meteorology did not occur until the 18th century. The 19th century saw modest progress in the field after weather observation networks were formed across broad regions. Prior attempts at prediction of weather depended on historical data. It was not until after the elucidation of the laws of physics and more particularly, the development of the computer, allowing for the automated solution of a great many equations that model the weather, in the latter half of the 20th century that significant breakthroughs in weather forecasting were achieved. An important domain of weather forecasting is marine weather forecasting as it relates to maritime and coastal safety, in which weather effects also include atmospheric interactions with large bodies of water.
This article describes severe weather terminology used by the National Weather Service (NWS) in the United States. The NWS, a government agency operating as an arm of the National Oceanic and Atmospheric Administration (NOAA) branch of the United States Department of Commerce (DoC), defines precise meanings for nearly all of its weather terms. This article describes NWS terminology and related weather scales used by the agency. Some terms may be specific to certain cities or regions.
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.
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, heavy precipitation, heavy freezing rain, strong winds, or wind transporting some substance through the atmosphere as in a dust storm, blizzard, sandstorm, etc.
These are some notable tornadoes, tornado outbreaks, and tornado outbreak sequences that have occurred around the globe.
This is a list of meteorology topics. The terms relate to meteorology, the interdisciplinary scientific study of the atmosphere that focuses on weather processes and forecasting.
A mesoscale convective system (MCS) is a complex of thunderstorms that becomes organized on a scale larger than the individual thunderstorms but smaller than extratropical cyclones, and normally persists for several hours or more. A mesoscale convective system's overall cloud and precipitation pattern may be round or linear in shape, and include weather systems such as tropical cyclones, squall lines, lake-effect snow events, polar lows, and Mesoscale Convective Complexes (MCCs), and generally form near weather fronts. The type that forms during the warm season over land has been noted across North America, Europe, and Asia, with a maximum in activity noted during the late afternoon and evening hours.
Tropical Storm Bill was a tropical storm that affected the Gulf Coast of the United States in the summer of 2003. The second storm of the 2003 Atlantic hurricane season, Bill developed from a tropical wave on June 29 to the north of the Yucatán Peninsula. It slowly organized as it moved northward, and reached a peak of 60 miles per hour (97 km/h) shortly before making landfall in south-central Louisiana. Bill quickly weakened over land, and as it accelerated to the northeast, moisture from the storm, combined with cold air from an approaching cold front, produced an outbreak of 34 tornadoes. Bill became extratropical on July 2, and was absorbed by the cold front later that day.
This article describes severe weather terminology used by the Meteorological Service of Canada, a branch within Environment and Climate Change Canada. The article primarily describes various weather warnings, and their criteria. Related weather scales and general weather terms are also addressed in this article. Some terms are specific to certain regions.
A superstorm is a large, destructive storm without another distinct meteorological classification, such as hurricane or blizzard. As the term is of recent coinage and lacks a formal definition, there is some debate as to its usefulness.
European windstorms are the strongest extratropical cyclones which occur across the continent of Europe. They form as cyclonic windstorms associated with areas of low atmospheric pressure. They are most common in the autumn and winter months. On average, the month when most windstorms form is January. The seasonal average is 4.6 windstorms. Deep low pressure areas are relatively common over the North Atlantic, sometimes starting as nor'easters off the New England coast, and frequently track across the North Atlantic Ocean towards western Europe, past the north coast of Great Britain and Ireland and into the Norwegian Sea. However, when they track further south, they can affect almost any country in Europe. Commonly affected countries include the United Kingdom, Ireland, the Netherlands, Norway, the Faroe Islands and Iceland, but any country in Central Europe, Northern Europe and especially Western Europe is occasionally struck by such a storm system.
Hurricane Darby was the first Eastern Pacific major hurricane since Hurricane Kenna in 2002. The sixth tropical cyclone, fourth named storm, and second hurricane of the 2004 Pacific hurricane season, Darby developed from a tropical wave that emerged from the west coast of Africa on July 12. After crossing into the Eastern Pacific, the storm became a tropical depression on June 26. The system steadily intensified, and became a hurricane on 000 UTC July 28. Darby peaked as a Category 3 hurricane on the Saffir-Simpson Hurricane Scale, though it quickly deteriorated due to cooler waters and increasing wind shear. While Darby dissipated on August 1, the remnants of the tropical cyclone affected the Hawaiian Islands. The system produced high waves and heavy rainfall that led to extensive flash flooding. Numerous roads were closed, while minor landslides and rockslides were reported. Despite the effects, no fatalities or severe damages occurred.
Hurricane Babe was the second named storm and the first to impact the United States during the below-average 1977 Atlantic hurricane season. Forming out of a tropical wave on September 3, Babe began as a subtropical cyclone in the eastern Gulf of Mexico. The storm gradually intensified as it tracked westward. On September 5, the storm turned north and acquired enough tropical characteristics. Later that day, Babe intensified into a hurricane and attained its peak strength with winds of 75 mph (120 km/h) and a barometric pressure of 995 mbar. Several hours later, the hurricane made landfall in Louisiana and quickly weakened. By September 6, Babe had weakened to a tropical depression and later dissipated early on September 9 over North Carolina.
A severe thunderstorm outbreak, also called a severe weather outbreak or simply a severe outbreak, is an event in which a weather system or combination of weather systems produces a multitude of severe thunderstorms in a region over a continuous span of time. A severe outbreak which is most notable for its tornadoes is called a tornado outbreak. The four kinds of severe weather produced in these outbreaks are tornadoes, severe wind, large hail, and flash flooding.
The following is a glossary of tornado terms. It includes scientific as well as selected informal terminology.
Storm Data and Unusual Weather Phenomena (SD) is a monthly NOAA publication with comprehensive listings and detailed summaries of severe weather occurrences in the United States. Included is information on tornadoes, high wind events, hail, lightning, floods and flash floods, tropical cyclones (hurricanes), ice storms, snow, extreme temperatures such as heat waves and cold waves, droughts, and wildfires. Photographs of weather and attendant damage are used as much as possible. Maps of significant weather are also included.
This glossary of meteorology is a list of terms and concepts relevant to meteorology and the atmospheric sciences, their sub-disciplines, and related fields.