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Severe Thunderstorms

Intense thunderstorms capable of producing heavy showers, flash floods, hail, strong and gusty surface winds, and tornadoes.

Ordinary Cell thunderstorms

A thunderstorm produced by local convection within conditionally unstable air maass. It often forms in the afternoon and dont not reach the intensity of a severe thunderstorm.

Cumulus Stage

The initial stage in the development of an ordinary cell thunderstorm in which rising, warm, humid air develops into a cumulus cloud.

Mature stage

The second stage in the three-stage cycle of an ordinary thunderstorm. This mature stage is characterized by heavy showers, lightning, thunder, and violent vertial motions inside cumulonimbus clouds.

dissipating stage

The final stage in the development of the ordinary cell thunderstorm when downdrafts exsist throught the cumulonimbus cloud

multi-cell storm

Thunderstorms often in a line each of which may be in different stage of its life cycle

squall line

a line of thunderstorms that form along a cold front or out ahead of it

mesoscale convective complexes

A large organized convective weather dydtem comprised of a numver of individual thunderstorms. The size of an MCC can be 1000 times larger than an individual ordinary thunderstorms

dryline

a boundary that separates warm, dry, air from warm, moist air. it usually represents a zone of instability along which thunderstorms form

gust front

A boundary that seperates a cold downdraft of a thunderstorm from warm, humid surface air. On the surface its passage resembles that of a cold front

shelf cloud

a dense, arch-shaped, omnious-looking cloud that often forms along the leading edge of a thunderstorm's gust front, especially when stable air rises up and over cooler air at the surface. also called an arcus cloud

roll cloud

a dense, cylindrical, elongated cloud that appears to slowly spin about a horizontal axis behind the leading edge of a thunderstorms gust front

outflow boundary

a surface boundary seperating cooler more-dense air from warmer less-dense air. outflow boundaries form by the horizontal spreading of cool air that originated inside a thunderstorm

downburst

A severe localized downdraft that can be experienced beneath a severe thunderstorm

microburst

A strong localized downdraft less than 4km wide that occurs beneth thunderstorms. A strong downburst greater across is called a macroburst.

bow echo

a line of thunderstorms on a radar screen taht appears in the shape of a bow. bow echos are often associated with damaging straight-line winds and small tornadoes

derecho

Strong,damaging, straight line winds assosiated with a cluster of severe thunderstorms that most often form in the evening or at night

heat burst

A sudden increase in surface air temperature often accompanied by extreme drying. a heat burst is associated with the downdraft of a thunderstorm, or a cluster of thunderstorms

lightning

a visivle electrical discharge produced by thunderstorms

thunder

the sound due to rapidley expanding gases along the channel of a lightning discharge

stepped leader

an initial discharge of electrons that proceeds intermittently toward the ground in a series of steps in a cloud-to-gound lightning stroke

dart leader

the discharge of electrons that proceeds intermittently toward the ground along the same ionized channel taken by the initial lightning stroke

dry lightning

lightning that occurs with thunderstorms that produce little, if any, appreciatable precipitation that reaches the surface

heat lightning

distant lightning that illuminates the sky but is too far away for its thunder to be heard

st. elmo's fire

a bright electric discharge that is projected from objects when they are in a strong electric field, such as during a thunderstorm...

return stroke

the luminous lightning stroke that propagates upward from the earth to the base of a cloud

tornado

an intense, rotating column of air that often protrudes from a cumulonimbus cloud in the shape of a funnel or a rope whose circulation is present of the ground.

funnel cloud

a tornado whose circulation has not reached the ground. often appears as a rotating conelike cloud that extends downward from the base of the thunderstorm

tornado outbreak

a series of tornadoes that forms within a perticular region- a region that may include several states. often associtaed with widesread damage and destruction

suction vortices

small, rapidly rotating whirls perhaps 10m in diameter that are found within large tornadoes

tornado watch

a forecast issued to alert the public that tornadoes may develop within a specified area

tornado warning

a warning issued when a tornado has actually been observed either visually or on a radar screen. it is also issued when the formation of tornadoes is imminent

fujita scale

A scale developed by t. theodore fujita for classifying tornadoes according to the damage they cause and their rotational wind speed

supercell tornadoes

tornadoes that occur within supercell thunderstorms that contain well-developed mid level mesocyclones

mesocyclone

a vertical column of cyclonically rotating air within a supercell thunderstorm

hook echo

the shape of an echo on a doppler radar screen that indicates the possible presence of a tornado

wall cloud

an area of rotating clouds that extends beneath a supercall thunderstorm and from which a funnel cloud may appear. also called a collar cloud and pedestal cloud

nonsupercell tornadoes

a tornado that occurs with a cloud that is often in its frowing stage and one that does not contain a mid-level mesocyclone of wall cloud. landspouts and gustanadoes are examples of nonsupercall tornados.

gustnadoes

a relatively weak tornado associated with a thunderstorm's outflow. It most often forms along the gust front.

landspouts

Realatively weak nonsupercall tornado that originates with a cumuliform cloud in its growth stage and with a cloud that does not contain a mid-level mesocyclone. Its spin originates near the surface. Landspouts often look like water spouts over land.

NEXRAD

an acronym for next generation weather radar. the main component of NEXRAD is the wsr 88-d doppler radar

waterspout

a column of rotating wind over water that has characteristics of a dust devil and tornado

sonic boom

a loud explosive-like sound caused by a shock wave emanating from an aircraft traveling at or above the speed of sound

flash floods

A flood that rises and falls quite rapidly with little or no advance warning, usually as the result of intanse rain fall over a relatively small area.

supercell storm

an enormous severe thunderstorm that consists primarily of a single rotating updraft. its organized internal structure allows that storm to maintain itself for several hours. the storm can produce large hail and dangerous tornadoes

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