Severe weather

severesevere weather warningsevere-weatherquite volatilesevere stormextreme weatherhazardous weathersevere and tropical weathersevere stormssevere thunderstorm
Severe weather refers to any dangerous meteorological phenomena with the potential to cause damage, serious social disruption, or loss of human life.wikipedia
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Extreme weather

extreme weather eventsweather extremesclimate extremes
The term severe weather is technically not the same phenomenon as extreme weather.
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.

Derecho

Super-DerechoblowdownDerechos
However, the most severe hail and tornadoes are produced by supercell thunderstorms, and the worst downbursts and derechos (straight-line winds) are produced by bow echoes.
A derecho (, from derecho, "straight") is a widespread, long-lived, straight-line wind storm that is associated with a fast-moving group of severe thunderstorms known as a mesoscale convective system.

Weather radar

Doppler weather radarradarDoppler radar
If a tornado is occurring (a tornado has been seen by spotters) or is imminent (Doppler weather radar has observed strong rotation in a storm, indicating an incipient tornado), the severe thunderstorm warning will be superseded by a tornado warning in the United States and Canada.
Both types of data can be analyzed to determine the structure of storms and their potential to cause severe weather.

Wind shear

windshearvertical wind shearshear
Both of these types of storms tend to form in environments high in wind shear.
Strong vertical wind shear within the troposphere also inhibits tropical cyclone development, but helps to organize individual thunderstorms into longer life cycles which can then produce severe weather.

Weather spotting

weather spotterweather spotterscooperative observers
If a tornado is occurring (a tornado has been seen by spotters) or is imminent (Doppler weather radar has observed strong rotation in a storm, indicating an incipient tornado), the severe thunderstorm warning will be superseded by a tornado warning in the United States and Canada.
In the U.S., these volunteers are usually trained by the National Weather Service or local Skywarn group, and are given a phone number, internet outlet, or amateur radio frequency to report to if a severe weather event, such as a tornado, severe thunderstorm, or flash flood occurs where the spotter is located.

Wind

windsgustsgust
High winds, hail, excessive precipitation, and wildfires are forms and effects of severe weather, as are thunderstorms, downbursts, tornadoes, waterspouts, tropical cyclones, and extratropical cyclones.
Strong vertical wind shear within the troposphere also inhibits tropical cyclone development, but helps to organize individual thunderstorms into living longer life cycles that can then produce severe weather.

Tornado

tornadoestornadicwedge tornado
High winds, hail, excessive precipitation, and wildfires are forms and effects of severe weather, as are thunderstorms, downbursts, tornadoes, waterspouts, tropical cyclones, and extratropical cyclones.
Increased moisture can fuel an increase in severe weather and tornado activity, particularly in the cool season.

Atmospheric convection

convectionconvectiveconvective activity
These convective downbursts can produce damaging winds, lasting 5 to 30 minutes, with wind speeds as high as 168 mph, and cause tornado-like damage on the ground.
Moist convection leads to thunderstorm development, which is often responsible for severe weather throughout the world.

Atmospheric instability

instabilityunstableAtmospheric stability
Organized severe weather occurs from the same conditions that generate ordinary thunderstorms: atmospheric moisture, lift (often from thermals), and instability.
Thunderstorms are expected with values below −2, and severe weather is anticipated with values below −6.

Significant weather advisory

Significant Weather Alertevacuation advisory
In the United States, such storms will usually warrant a Significant Weather Alert.
If severe weather is detected, alerts (mainly a severe thunderstorm or tornado warning) are issued by the National Weather Service (effectively replacing a significant weather advisory), and the Emergency Alert System may activate and broadcast the alert.

Wake low

A wake low or a mesoscale low-pressure area forms behind the rain shield (a high pressure system under the rain canopy) of a mature squall line and is sometimes associated with a heat burst.
Severe weather, in the form of high winds, can be generated by the wake low when the pressure difference between the mesohigh preceding it and the wake low is intense enough.

Thunderstorm

thunderstormssevere thunderstormelectrical storm
High winds, hail, excessive precipitation, and wildfires are forms and effects of severe weather, as are thunderstorms, downbursts, tornadoes, waterspouts, tropical cyclones, and extratropical cyclones.
Severe weather in the form of strong straight-line winds can be expected in areas where the squall line itself is in the shape of a bow echo, within the portion of the line that bows out the most.

National Weather Service

United States Weather BureauWeather BureauU.S. Weather Bureau
Both severe and significant severe events warrant a severe thunderstorm warning from the United States National Weather Service (excludes flash floods), the Environment Canada, the Australian Bureau of Meteorology, the Meteorological Service of New Zealand and the Meteorological Office UK, if the event occurs in those countries.
NWWS delivers severe weather and storm warnings to users in ten seconds or less from the time of their issuance, making it the fastest delivery system available.

Cold-core low

upper-level lowcold-coreupper-level trough
Meteorologically, excessive rains occur within a plume of air with high amounts of moisture (also known as an atmospheric river) which is directed around an upper level cold-core low or a tropical cyclone.
Severe weather, such as tornadoes, can occur near the center of cold-core lows.

Beaufort scale

gale forcehurricane-forcegale-force
Nor'easters may cause coastal flooding, coastal erosion, and hurricane-force winds.
Today, many countries have abandoned the scale and use the metric system based units, m/s or km/h, instead, but the severe weather warnings given to the public are still approximately the same as when using the Beaufort scale.

Severe thunderstorm warning

severe thunderstormsevereSevere Thunderstorm '''Warning
Both severe and significant severe events warrant a severe thunderstorm warning from the United States National Weather Service (excludes flash floods), the Environment Canada, the Australian Bureau of Meteorology, the Meteorological Service of New Zealand and the Meteorological Office UK, if the event occurs in those countries.

Storm chasing

storm chaserstorm chaserschasers
Storm chasing is broadly defined as the pursuit of any severe weather condition, regardless of motive, which can be curiosity, adventure, scientific investigation, or for news or media coverage.

Cyclone

cyclonescycloniccyclonic storm
Although cyclones take an enormous toll in lives and personal property, they are also important factors in the precipitation regimes of areas they affect.
Strong cold fronts typically feature narrow bands of thunderstorms and severe weather, and may on occasion be preceded by squall lines or dry lines.

Synoptic scale meteorology

synoptic scalesynopticsynoptic-scale
A synoptic-scale extratropical storm along the East Coast of the United States and Atlantic Canada is called a Nor'easter.
Cold fronts may feature narrow bands of thunderstorms and severe weather, and may on occasion be preceded by squall lines or dry lines.

Hail

hailstormhailstoneshailstone
High winds, hail, excessive precipitation, and wildfires are forms and effects of severe weather, as are thunderstorms, downbursts, tornadoes, waterspouts, tropical cyclones, and extratropical cyclones.

Altitude

high altitudealtitudeshigh-altitude
Types of severe weather phenomena vary, depending on the latitude, altitude, topography, and atmospheric conditions.

Topography

topographicaltopographictopographer
Types of severe weather phenomena vary, depending on the latitude, altitude, topography, and atmospheric conditions.

Atmosphere

atmosphericatmospheresplanetary atmospheres
Types of severe weather phenomena vary, depending on the latitude, altitude, topography, and atmospheric conditions.

Precipitation

rainfallhydrometeorannual precipitation
High winds, hail, excessive precipitation, and wildfires are forms and effects of severe weather, as are thunderstorms, downbursts, tornadoes, waterspouts, tropical cyclones, and extratropical cyclones.

Wildfire

forest fireforest fireswildfires
High winds, hail, excessive precipitation, and wildfires are forms and effects of severe weather, as are thunderstorms, downbursts, tornadoes, waterspouts, tropical cyclones, and extratropical cyclones.