Cumulonimbus (from Latin cumulus 'swell' and nimbus 'cloud') 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. Above the lower portions of the cumulonimbus the water vapor becomes ice crystals , such as snow and graupel , the interaction of which can lead to hail and to lightning formation, respectively.
17-587: A thunderhead is a cumulonimbus cloud seen during a thunderstorm. Thunderhead may also refer to: 8 Thunderhead (Character) Alter-Ego of Hank Williams Jr. Cumulonimbus cloud When causing thunderstorms , these clouds may be called thunderheads . Cumulonimbus can form alone, in clusters, or along squall lines . These clouds are capable of producing lightning and other dangerous severe weather , such as tornadoes , hazardous winds , and large hailstones. Cumulonimbus progress from overdeveloped cumulus congestus clouds and may further develop as part of
34-712: A supercell . Cumulonimbus is abbreviated as Cb . Towering cumulonimbus clouds are typically accompanied by smaller cumulus clouds. The cumulonimbus base may extend several kilometres (miles) across, or be as small as several tens of metres (yards) across, and occupy low to upper altitudes within the troposphere - formed at altitude from approximately 200 to 4,000 m (700 to 10,000 ft). Normal peaks usually reach to as much as 12,000 m (39,000 ft), with unusually high ones typically topping out around 20,000 m (66,000 ft) and extreme instances claimed to be as high as 21,000 m (69,000 ft) or more. Well-developed cumulonimbus clouds are characterized by
51-607: A 24 km (15 mi) diameter and a height of approximately 12.2 km (40,000 ft). Depending on the conditions present in the atmosphere, these three stages take an average of 30 minutes to go through. Clouds form when the dew point temperature of water is reached in the presence of condensation nuclei in the troposphere. The atmosphere is a dynamic system, and the local conditions of turbulence, uplift , and other parameters give rise to many types of clouds. Various types of cloud occur frequently enough to have been categorized. Furthermore, some atmospheric processes can make
68-500: A cumulonimbus is often intense with downbursts being responsible for many accidents in earlier decades before training and technological detection and nowcasting measures were implemented. A small form of downburst, the microburst, is the most often implicated in crashes because of their rapid onset and swift changes in wind and aerodynamic conditions over short distances. Most downbursts are associated with visible precipitation shafts, however, dry microbursts are generally invisible to
85-524: A flat, anvil shaped top (anvil dome), caused by wind shear or inversion at the equilibrium level near the tropopause . The shelf of the anvil may precede the main cloud's vertical component for many kilometres (miles), and be accompanied by lightning. Occasionally, rising air parcels surpass the equilibrium level (due to momentum) and form an overshooting top culminating at the maximum parcel level . When vertically developed, this largest of all clouds usually extends through all three cloud regions. Even
102-811: Is sufficient instability and moisture in the atmosphere , however (on a hot summer day, for example), the outflowing moisture and gusts from one storm cell can lead to new cells forming just a few kilometres (miles) from the former one a few tens of minutes later or in some cases hundreds of kilometres (miles) away many hours later. This process cause thunderstorm formation (and decay) to last for several hours or even over multiple days. Cumulonimbus clouds can also occur as dangerous winter storms called " thundersnow " which are associated with particularly intense snowfall rates and with blizzard conditions when accompanied by strong winds that further reduce visibility . However, cumulonimbus clouds are most common in tropical regions and are also frequent in moist environments during
119-459: The Age of Sail , a vessel always sought to use the wind to its advantage, maneuvering if possible to attack from windward. This was particularly important for less maneuverable square-rigged warships, which had limited ability to sail upwind, and sought to "hold the weather gage " entering battle. This was particularly important once artillery was introduced to naval warfare. Ships heel away from
136-424: The Age of Sail , the term weather was used as a synonym for windward in some contexts, as in the weather gage . Since it captures rainfall , the windward side of a mountain tends to be wetter than the leeward side it blocks. The drier leeward area is said to be in a rain shadow . The term "windward" has roots in both Low German and Old English. The word "lee", which means a place without wind, comes from
153-406: The wind . Windward is upwind from the point of reference, i.e., towards the direction from which the wind is coming; leeward is downwind from the point of reference, i.e., along the direction towards which the wind is going. The side of a ship that is towards the leeward is its "lee side". If the vessel is heeling under the pressure of crosswind , the lee side will be the "lower side". During
170-553: The Old Norse "hle" for "cover" and has been used in marine navigation in Germany since medieval times. The word "wind," meaning "air in motion," comes from Proto-Germanic *winda- and has evolved over time, with pronunciation changes influenced by similar words like "windy." The word "wind" has been associated with emptiness and vanity since the late 13th century. Additionally, "wind" has been used figuratively in phrases like "which way
187-404: The clouds organize in distinct patterns such as wave clouds or actinoform clouds . These are large-scale structures and are not always readily identifiable from a single point of view. Downwind In geography and seamanship , windward ( / ˈ w ɪ n d w ər d , ˈ w ɪ n ər d / ) and leeward ( / ˈ l iː w ər d , ˈ lj uː ər d / ) are directions relative to
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#1732786842738204-443: The naked eye. At least one fatal commercial airline accident was associated with flying through a tornado. In general, cumulonimbus require moisture, an unstable air mass , and a lifting force in order to form. Cumulonimbus typically go through three stages: the developing stage , the mature stage (where the main cloud may reach supercell status in favorable conditions), and the dissipation stage . The average thunderstorm has
221-517: The same meaning are widely used, particularly upwind and downwind . Among sailing craft, the windward vessel is normally the more maneuverable. For this reason, rule 12 of the International Regulations for Preventing Collisions at Sea , applying to sailing vessels, stipulates that where two are sailing in similar directions in relation to the wind, the windward vessel gives way to the leeward vessel. In naval warfare during
238-400: The smallest cumulonimbus cloud dwarfs its neighbors in comparison. Cumulonimbus storm cells can produce torrential rain of a convective nature (often in the form of a rain shaft ) and flash flooding , as well as straight-line winds . Most storm cells die after about 20 minutes, when the precipitation causes more downdraft than updraft , causing the energy to dissipate. If there
255-476: The warm season in the middle latitudes . A dust storm caused by a cumulonimbus downburst is a haboob . Cumulonimbus are a notable hazard to aviation due most importantly to potent wind currents but also reduced visibility and lightning, as well as icing and hail if flying inside the cloud. Within and in the vicinity of thunderstorms there is significant turbulence and clear-air turbulence (particularly downwind ), respectively. Wind shear within and under
272-657: The wind blows" to indicate the current state of affairs. The suffix "-ward," meaning "toward," is an adverbial suffix in Old English derived from Proto-Germanic *werda-, which itself comes from the PIE root *wer- meaning "to turn, bend." The original notion of "-ward" is "turned toward." Windward and leeward directions (and the points of sail they create) are important factors to consider in such wind-powered or wind-impacted activities as sailing , wind-surfing , gliding , hang-gliding , and parachuting . Other terms with broadly
289-419: The wind, so the leeward vessel would expose more of her topsides to shot, in extreme cases even part of her bottom. The terms windward and leeward are used in reference both to sides (and climates ) of individual islands and relative island locations in an archipelago . The windward side of an island is subject to the prevailing wind , and is thus the wetter (see orographic precipitation ). The leeward side
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