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A multicellular thunderstorm cluster is a
The formation of multicellular thunderstorms imply that the updraft in the mother thunderstorm is offset from its downdraft. New cells usually form in the upwind (usually western or southwestern) part of the storm where the downdrafts of the mature cells meet the environmental wind, lifting air parcels and triggering new convection. The mature cells are thus usually in the center of the storm, and dissipating cells are usually in the downwind (usually eastern or northeastern) part of the storm.
PDF at hs-staffserver.stjames.k12.mn.us
* * {{cite web, url=https://www.weather.gov/media/ilx/Spotter_Training/Spotters%20Guide_New.pdf , title=NOAA spotter's guide Severe weather and convection Atmospheric electricity
thunderstorm
A thunderstorm, also known as an electrical storm or a lightning storm, is a storm characterized by the presence of lightning and its acoustics, acoustic effect on the Earth's atmosphere, known as thunder. Relatively weak thunderstorm ...
that is composed of multiple convective cells, each being at a different stage in the life cycle of a thunderstorm. It appears as several anvils clustered together. A cell is an updraft/downdraft couplet. These different cells will dissipate as new cells form and continue the life of the multicellular thunderstorm cluster with each cell taking a turn as the dominant cell in the group.
Description
The formation of multicellular thunderstorms imply that the updraft in the mother thunderstorm is offset from its downdraft. New cells usually form in the upwind (usually western or southwestern) part of the storm where the downdrafts of the mature cells meet the environmental wind, lifting air parcels and triggering new convection. The mature cells are thus usually in the center of the storm, and dissipating cells are usually in the downwind (usually eastern or northeastern) part of the storm.
Characteristics
The multicellular cluster can last for hours while each individual cell should only last for about 20 to 60 minutes. These storms can sometimes be severe and sometimes have awkward paths due to the thunderstorm sometimes not following the path of the cells that compose it. The typical hodograph, plot of the wind versus altitude, associated with it shows a linearwind shear
Wind shear (; also written windshear), sometimes referred to as wind gradient, is a difference in wind speed and/or direction over a relatively short distance in the atmosphere. Atmospheric wind shear is normally described as either vertical ...
with altitude The moderate vertical wind shear leads to the development of a non-symmetric surface convergence associated with the thunderstorm outflow, with the strongest convergence taking place on the downwind side from the storm's motion. So while individual cells move along the windshear, the line moves at 30° of it, at 70% of the mean wind speed in the layer.
The Convective available potential energy (CAPE) is moderate to large, usually between 800 and 1,500 J/kg. The radar structure of this type of thunderstorm is characterized by overhangs of reflectivity in the southwestern part of the cluster.
Threats
Any severe activity in one of these storms will most likely come from the dominant cell near or after its peak updraft strength. This is because there could be severehail
Hail is a form of solid Precipitation (meteorology), 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 hailsto ...
from a strong updraft that lasts only a short period of time, with damaging winds.
Rain is an important impact of such systems. The speed and direction at which the entire cluster of thunderstorms move downstream make the difference in the amount of rain received in any one location. Individual cells might move downstream but additional cells forming upwind of the cluster can move directly over the path of the previous cell, forming training echoes.
A multicellular storm can sometimes develop into a mesoscale convective system
A mesoscale convective system (MCS) is a complex of thunderstorms that becomes organized on a scale larger than the individual thunderstorms but smaller than extratropical cyclones, and normally persists for several hours or more. A mesoscale conv ...
(MCS) or be a squall line
A squall line, or quasi-linear convective system (QLCS), is a line of thunderstorms, often forming along or ahead of a cold front. In the early 20th century, the term was used as a synonym for cold front (which often are accompanied by abrupt a ...
. Updrafts reform new cells continually at the leading edge of system with rain and hail following behind. Individual thunderstorm updrafts and downdrafts along the line can become strong, producing large hail and strong outflow of straight-line winds ahead of system. Tornadoes are only occasionally reported. In certain conditions, squall line can extend on a very long line, moving extremely rapidly, and become a derecho
A ''derecho'' (, from , 'straight') is a widespread, long-lived, straight-line wind storm that is associated with a fast-moving group of Severe weather#Categories, severe thunderstorms known as a mesoscale convective system.
Derechos cause Bea ...
.
See also
* Pulse storm *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 (su ...
References
External links
PDF at hs-staffserver.stjames.k12.mn.us
* * {{cite web, url=https://www.weather.gov/media/ilx/Spotter_Training/Spotters%20Guide_New.pdf , title=NOAA spotter's guide Severe weather and convection Atmospheric electricity