Gustnado
Encyclopedia
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...
", as gustnadoes form due to non-tornadic cyclonic features in the downdraft from the gust (outflow) front of a strong thunderstorm, especially one which has become outflow dominated. It has little in common with tornadoes structurally in terms of vertical development, or in regard to intensity, longevity, and formative process (as classic 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...
es are associated with mesocyclone
Mesocyclone
A mesocyclone is a vortex of air, approximately 2 to 10 miles in diameter , within a convective storm....
s in the upflow of the storm, not the outflow).
The average gustnado lasts a few seconds to a few minutes, although there can be several generations and simultaneous swarms. Most have the winds of an F0 or F1 tornado, and are commonly mistaken for tornadoes. However, unlike tornadoes, the rotating column of air in a gustnado usually does not extend all the way to the base of the thundercloud. Gustnadoes actually have more in common with whirlwinds
Whirlwind (atmospheric phenomenon)
A whirlwind is a weather phenomenon in which a vortex of wind forms due to instabilities and turbulence created by heating and flow gradients. Whirlwinds occur all over the world and in any season....
(which include dust devils
Dust Devils
Dust Devils is an independently published role-playing game set in the Old West, written by Matt Snyder. It was voted the 2002 Indie RPG of the Year; it also won the Best Synergy of Game and Rules category, as well as placing in the Best Production and Most Innovative Game categories.The game uses...
, whirlwinds that form due to superheated surface layers and stretched vorticity, most commonly on sunny, warm days with light winds). They are not considered true tornadoes (unless they connect the surface to the ambient cloud base) by most meteorologists and are not included in tornado statistics. Sometimes referred to as spin-up tornadoes, that term more correctly describes the rare tornadic gustnado that connects the surface to the ambient clouded base, or to relatively brief tornadoes associated with a mesovortex.
The most common setting for a gustnado is on the outflow from a severe thunderstorm (58+ mph winds). The cool air in the gust front acts like a mesoscale
Mesoscale meteorology
Mesoscale meteorology is the study of weather systems smaller than synoptic scale systems but larger than microscale and storm-scale cumulus systems. Horizontal dimensions generally range from around 5 kilometers to several hundred kilometers...
cold front
Cold front
A cold front is defined as the leading edge of a cooler mass of air, replacing a warmer mass of air.-Development of cold front:The cooler and denser air wedges under the less-dense warmer air, lifting it...
. It slices under the warm air ahead of it, creating upward motions and turbulent interactions. The friction from this interaction creates a spinning column of air, or eddy
Eddy (fluid dynamics)
In fluid dynamics, an eddy is the swirling of a fluid and the reverse current created when the fluid flows past an obstacle. The moving fluid creates a space devoid of downstream-flowing fluid on the downstream side of the object...
, which can create a gustnado (to get the general idea of this, picture an area of leaves swirling on a windy day, just on a much larger scale).
In addition to forming on the leading edge of a thunderstorm, gustnadoes are also not uncommon in the rear-flank downdraft of supercells. This region often contains high vorticity air, and sometimes highly buoyant air, both of which are conducive to the formation of gustnadoes as well as tornadoes. Gustnadoes near the updraft-downdraft interface may evolve into bona fide tornadoes when ingested into a mesocyclone.
Although "gustnado" has yet to enter accepted weather nomenclature
Nomenclature
Nomenclature is a term that applies to either a list of names or terms, or to the system of principles, procedures and terms related to naming - which is the assigning of a word or phrase to a particular object or property...
, the term is popular in the Great Plains and Midwest of the United States, where the phenomenon is most common.
While injuries or deaths are rare from gustadoes, strong ones can cause damage. There is some speculation that a gustnado might be responsible for the collapse of a stage at the Indiana State Fair
Indiana State Fair stage collapse
The Indiana State Fair stage collapse occurred in the Indiana State Fairgrounds grandstand on August 13, 2011 at the Indiana State Fair in Indianapolis...
on August 13th, 2011 which killed 5 people.