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An overshooting top (or penetrating top) is a dome-like protrusion shooting out of the top of the
anvil An anvil is a metalworking tool consisting of a large block of metal (usually forged or cast steel), with a flattened top surface, upon which another object is struck (or "worked"). Anvils are as massive as practical, because the higher ...
of a
thunderstorm 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 some ...
and into the lower
stratosphere The stratosphere () is the second layer of the atmosphere of the Earth, located above the troposphere and below the mesosphere. The stratosphere is an atmospheric layer composed of stratified temperature layers, with the warm layers of air h ...
. When an overshooting top is present for 10 minutes or longer, it is a strong indication that the storm is
severe Severity or Severely may refer to: * ''Severity'' (video game), a canceled video game * "Severely" (song), by South Korean band F.T. Island See also

* * {{disambig ...
.Chance Hayes, National Weather Service Wichita, Kansas. "Storm Fury on the Plains." Storm Spotter Training. 4H Building, Salina, Kansas. 22 Feb. 2010. Lecture.


Formation

When a thunderstorm forms, clouds build vertically into the atmosphere until the storm's
updraft In meteorology, an updraft is a small-scale current of rising air, often within a cloud. Overview Localized regions of warm or cool air will exhibit vertical movement. A mass of warm air will typically be less dense than the surrounding regi ...
(warm rising air) has reached an equilibrium level (EL); the point where the surrounding air is about the same temperature or even warmer. This point of equilibrium is often marked by the tropopause. Rather than continuing to rise into the stratosphere, the vertical cloud growth abruptly stops, and instead clouds spread horizontally, forming an "anvil" shape on top of the thunderstorm. An overshooting top forms when a thunderstorm's updraft, due to
momentum In Newtonian mechanics, momentum (more specifically linear momentum or translational momentum) is the product of the mass and velocity of an object. It is a vector quantity, possessing a magnitude and a direction. If is an object's mass ...
from rapid ascent and strength of lifting through the free convective layer (FCL), protrudes its equilibrium level, forming a dome-like structure above the anvil. This can occur with any
cumulonimbus cloud Cumulonimbus (from Latin ''cumulus'', "heaped" and ''nimbus'', "rainstorm") is a dense, towering vertical cloud, typically forming from water vapor condensing in the lower troposphere that builds upward carried by powerful buoyant air currents. ...
when instability is high. Whereas anvils form at the equilibrium level, overshooting tops continue to the maximum parcel level (MPL).


Severe weather

Many thunderstorms exhibit an overshooting top at some point in their life cycle. In weaker thunderstorms, the overshooting top is short-lived, and often takes on a wispy appearance. If the overshooting top is rising and falling in a cyclical fashion with each protrusion persisting only a few minutes, then it could indicate the storm is pulsing and not as strong as a storm with a continuous overshooting top. An overshooting top lasting for more than 10 minutes is a sign of a strong updraft in a thunderstorm, indicating a strong likelihood the storm is producing
severe weather Severe weather is any dangerous meteorological phenomenon with the potential to cause damage, serious social disruption, or loss of human life. Types of severe weather phenomena vary, depending on the latitude, altitude, topography, and atmos ...
. If the overshooting top is continuous, it's an indication of enhanced probability that the storm is a
supercell A supercell is a thunderstorm characterized by the presence of a mesocyclone: a deep, persistently rotating updraft. Due to this, these storms are sometimes referred to as rotating thunderstorms. Of the four classifications of thunderstorms ( ...
, i.e. a rotating storm. During a strong
tornado A tornado is a violently 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. It is often referred to as a twister, whirlwind or cyclone, alt ...
, the overshooting top may roll or fold over as new activity climbs up the back while the front of the overshooting top collapses into the storm. During a long-track tornado, the entire top of the storm, including the overshooting top, may drop by thousands of feet.


Storm features

A storm powerful enough to produce a lasting overshooting top typically produces the following: * Heavy
rain Rain is water droplets that have condensed from atmospheric water vapor and then fall under gravity. Rain is a major component of the water cycle and is responsible for depositing most of the fresh water on the Earth. It provides water f ...
; a deluge of
rain Rain is water droplets that have condensed from atmospheric water vapor and then fall under gravity. Rain is a major component of the water cycle and is responsible for depositing most of the fresh water on the Earth. It provides water f ...
could fall from this storm in a short amount of time. * Strong straight-line
wind Wind is the natural movement of air or other gases relative to a planet's surface. Winds occur on a range of scales, from thunderstorm flows lasting tens of minutes, to local breezes generated by heating of land surfaces and lasting a few ...
from
downburst In meteorology, a downburst is a strong downward and outward gushing wind system that emanates from a point source above and blows radially, that is, in straight lines in all directions from the area of impact at surface level. Capable of pro ...
s; the storm clouds have powerful winds churning inside them. These winds are likely to be felt at the surface and also a threat to aviation aloft. * Sometimes a
tornado A tornado is a violently 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. It is often referred to as a twister, whirlwind or cyclone, alt ...
may form; most strong tornadoes are associated with
mesocyclone A mesocyclone is a meso-gamma mesoscale (or storm scale) region of rotation (vortex), typically around in diameter, most often noticed on radar within thunderstorms. In the northern hemisphere it is usually located in the right rear flank (back ...
s located near the interchange of the rotating updraft and the
rear flank downdraft The rear flank downdraft (RFD) is a region of dry air wrapping around the back of a mesocyclone in a supercell thunderstorm. These areas of descending air are thought to be essential in the production of many supercellular tornadoes. Large hail ...
(RFD). *
Hail Hail is a form of solid precipitation. It is distinct from ice pellets (American English "sleet"), though the two are often confused. It consists of balls or irregular lumps of ice, each of which is called a hailstone. Ice pellets generally fal ...
; if the updraft is strong enough to produce an overshooting top it can also carry large
hail Hail is a form of solid precipitation. It is distinct from ice pellets (American English "sleet"), though the two are often confused. It consists of balls or irregular lumps of ice, each of which is called a hailstone. Ice pellets generally fal ...
. * A storm that features an overshooting top is a
thunderstorm 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 some ...
, and is thus likely to produce
lightning Lightning is a naturally occurring electrostatic discharge during which two electrically charged regions, both in the atmosphere or with one on the ground, temporarily neutralize themselves, causing the instantaneous release of an average ...
.


See also

*
Atmospheric convection Atmospheric convection is the result of a parcel-environment instability, or temperature difference layer in the atmosphere. Different lapse rates within dry and moist air masses lead to instability. Mixing of air during the day which expands the ...
*
Atmospheric thermodynamics Atmospheric thermodynamics is the study of heat-to- work transformations (and their reverse) that take place in the earth's atmosphere and manifest as weather or climate. Atmospheric thermodynamics use the laws of classical thermodynamics, to des ...


References


External links


http://www.theweatherprediction.com/habyhints/352
{{Cloud types Severe weather and convection Cloud and fog physics Cumulus