Overshooting top
Encyclopedia
An overshooting top is a dome-like protrusion that shoots out of the top of the anvil of a thunderstorm
. When an overshooting top is present for 10 minutes or longer, it is a strong indication that the thunderstorm may be severe.
(warm rising air) has reached an equilibrium level
; 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 tropopause, 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 from rapid ascent and strength of lifting, protrudes its equilibrium level, forming a dome-like structure on top of the anvil. This can occur with any cumulonimbus cloud
when instability is high.
An overshooting top lasting for more than 10 minutes is a sign of a strong updraft in a thunderstorm, indicating a strong likelihood that the storm is producing severe weather
. If the overshooting top is continuous it means the storm is probably a strong supercell
. During a strong tornado
, the overshooting top might roll over 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 whole top of the storm, including the overshooting top, might drop by thousands of feet.
Thunderstorm
A thunderstorm, also known as an electrical storm, a lightning storm, thundershower or simply a storm is a form of weather characterized by the presence of lightning and its acoustic effect on the Earth's atmosphere known as thunder. The meteorologically assigned cloud type associated with the...
. When an overshooting top is present for 10 minutes or longer, it is a strong indication that the thunderstorm may be severe.
Formation
When a thunderstorm forms, clouds build vertically into the atmosphere until the storm's updraftVertical draft
An updraft or downdraft is the vertical movement of air as a weather related phenomenon. One of two forces causes the air to move. Localized regions of warm or cool air will exhibit vertical movement. A mass of warm air will typically be less dense than the surrounding region, and so will rise...
(warm rising air) has reached an equilibrium level
Equilibrium level
In meteorology, the equilibrium level , or level of neutral buoyancy , or limit of convection , is the height at which a rising parcel of air is at a temperature of equal warmth to it....
; the point where the surrounding air is about the same temperature or even warmer. This point of equilibrium is often marked by the tropopause
Tropopause
The tropopause is the atmospheric boundary between the troposphere and the stratosphere.-Definition:Going upward from the surface, it is the point where air ceases to cool with height, and becomes almost completely dry...
. Rather than continuing to rise into the tropopause, 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 from rapid ascent and strength of lifting, protrudes its equilibrium level, forming a dome-like structure on top of the anvil. This can occur with any cumulonimbus cloud
Cumulonimbus cloud
Cumulonimbus is a towering vertical cloud that is very tall, dense, and involved in thunderstorms and other inclement weather. Cumulonimbus originates from Latin: Cumulus "Heap" and nimbus "rain". It is a result of atmospheric instability. These clouds can form alone, in clusters, or along a cold...
when instability is high.
Severe weather
Most thunderstorms will have 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, then it could indicate that 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 that the storm is producing severe weather
Severe weather
Severe weather phenomena are weather conditions that are hazardous to human life and property.- Examples Include :Severe weather can occur under a variety of situations, but three characteristics are generally needed: a temperature or moisture boundary, moisture, and , instability in the...
. If the overshooting top is continuous it means the storm is probably a strong supercell
Supercell
A supercell is a thunderstorm that is characterized by the presence of a mesocyclone: a deep, continuously-rotating updraft. For this reason, these storms are sometimes referred to as rotating thunderstorms...
. During a strong tornado
Tornado
A tornado is a violent, dangerous, 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. They are often referred to as a twister or a cyclone, although the word cyclone is used in meteorology in a wider...
, the overshooting top might roll over 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 whole top of the storm, including the overshooting top, might drop by thousands of feet.
Precipitation
A storm powerful enough to produce a lasting overshooting top will have the following:- Heavy rainRainRain is liquid precipitation, as opposed to non-liquid kinds of precipitation such as snow, hail and sleet. Rain requires the presence of a thick layer of the atmosphere to have temperatures above the melting point of water near and above the Earth's surface...
; a deluge of rain could fall from this storm in a short amount of time.
- strong windWindWind is the flow of gases on a large scale. On Earth, wind consists of the bulk movement of air. In outer space, solar wind is the movement of gases or charged particles from the sun through space, while planetary wind is the outgassing of light chemical elements from a planet's atmosphere into space...
; the storm clouds have powerful winds churning inside them. These winds are likely to be felt at the surface as well, possibly in the form of a tornado.
- HailHailHail is a form of solid precipitation. It consists of balls or irregular lumps of ice, each of which is referred to as a hail stone. Hail stones on Earth consist mostly of water ice and measure between and in diameter, with the larger stones coming from severe thunderstorms...
; if the updraft is strong enough to produce an overshooting top it can also carry large hail.
- LightningLightningLightning is an atmospheric electrostatic discharge accompanied by thunder, which typically occurs during thunderstorms, and sometimes during volcanic eruptions or dust storms...
; this storm is sure to be a thunderstorm.