| Cumulus congestus | |
|---|---|
 Cumulus congestus clouds looming over the horizon, as seen fromWagga Wagga,NSW, Australia | |
| Abbreviation | Cu con |
| Symbol |  |
| Genus | Cumulus ("heaped") |
| Species | Congestus ("piled up") |
| Variety |
|
| Altitude | Up to 6,000 m (Up to 20,000 ft) |
| Classification | Family D (Vertically developed) |
| Appearance | Low-altitude, vertical, taller than it is wide, fluffy heaps of clouds with cotton-like appearance. |
| Precipitation | Rain,snow, orsnow pellets.[1] |
Cumulus congestus ortowering cumulus clouds are aspecies ofcumulus that can be based in the low- to middle-height ranges. They achieve considerable vertical development in areas of deep, moistconvection. They are an intermediate stage betweencumulus mediocris andcumulonimbus, sometimes producingrainshowers, snow, orice pellets.[2]Precipitation thatevaporates before reaching the surface isvirga.
Cumulus congestus clouds are characteristic ofunstableregions ofatmosphere that are undergoingconvection. They are often characterized by sharp outlines and great vertical development.[1] Since strongupdrafts produce (and primarily compose) them, the clouds are typically taller than they are wide;cloud tops can reach 6 km (3.7 mi; 20,000 ft),[3] or higher in thetropics.[4]
Cumulus congestus clouds are formed by the development of cumulus mediocris generally, though they can also be formed fromaltocumulus castellanus orstratocumulus castellanus, which are forms ofcumulus castellanus.[1] Thecongestus species of cloud can only be found in the genuscumulus[1] and is designated astowering cumulus (TCu) by theInternational Civil Aviation Organization (ICAO).
Congestus clouds are capable of producing severeturbulence and showers of moderate to heavy intensity. This species is classified as vertical or multi-étage and is coded CL2 in the synop report. These clouds are usually too large and opaque to have any opacity or pattern-based varieties. Congestus and especially cumulonimbus arehazardous to aviation.
An approachingweather front often brings mid-level clouds (e.g.altostratus oraltocumulus), which when expansive and dense, reduces insolation and infringes cumulus from reaching the congestus stage. Occasionally however, particularly if the air below the mid-level cloud is very warm or unstable, some of the cumuli may become congestus and the tops of them may rise above the mid level cloud layer, sometimes resulting in showers ahead of the mainrainband. This is often a sign the approaching front contains at least a few cumulonimbi amongst thenimbostratus rain clouds, and therefore any rain may be accompanied bythunderstorms.[citation needed]
Cumulus congestus will develop intocumulonimbus calvus under conditions of sufficientinstability. This transformation can be seen by the presence of smooth, fibrous, or striated aspects assumed by the cloud's upper part.[5] While all congestus produce showers, this development could produce heavyprecipitation.[1]
Aflammagenitus cloud, or pyrocumulus, (FgCu or FgCu con) is a rapidly growing convective cloud associated withvolcanic eruptions and large-scale fires (typicallywildfires). Pyrocumulus congestus may thus form under those special circumstances that can also cause severe turbulence.
Cumulus congestus can also be associated withfair weather waterspouts forming from rotation at the open water surface being stretched and tightened under theirupdraft.[6]Landspouts most often form under congestus, as well. Both of these non-mesocyclone associatedtornadoes typically dissipate when a more pronouncedprecipitation shaft forms and thedowndraft cuts off this process. In highlysheared environments or within theflanking line of asupercell, congestus can rotate and, on rare occasions, produce mesocyclonic-type tornadoes, with waterspouts and landspouts emanating from misocyclones (a related but distinct process).
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Turkey tower is aslang term for a narrow, tall, individual towering cloud from a small cumulus cloud which develops and suddenly falls apart.[7] Sudden development of turkey towers could signify the breaking or weakening of acapping inversion,[8] and an area where these consistently form is an "agitated area", a term that applies to congestus generally.
