Cloud suck is a phenomenon commonly known in

paragliding Paragliding is the recreational and competitive adventure sport of flying paragliders: lightweight, free-flying, foot-launched glider aircraft with no rigid primary structure. The pilot sits in a harness or in a cocoon-like 'pod' suspended be ...

hang gliding Hang gliding is an air sports, air sport or recreational activity in which a pilot flies a light, non-motorised, fixed-wing aircraft, fixed-wing heavier-than-air aircraft called a hang glider. Most modern hang gliders are made of an aluminium al ...

, and

sailplane A glider or sailplane is a type of glider aircraft used in the leisure activity and sport of gliding (also called soaring). This unpowered aircraft can use naturally occurring currents of rising air in the atmosphere to gain altitude. Sailplan ...

flying where pilots experience significant

lift Lift or LIFT may refer to: Physical devices * Elevator, or lift, a device used for raising and lowering people or goods ** Paternoster lift, a type of lift using a continuous chain of cars which do not stop ** Patient lift, or Hoyer lift, mobile ...

due to a

thermal A thermal column (or thermal) is a rising mass of buoyant air, a convective current in the atmosphere, that transfers heat energy vertically. Thermals are created by the uneven heating of Earth's surface from solar radiation, and are an example ...

under the base of

cumulus Cumulus clouds are clouds that have flat bases and are often described as puffy, cotton-like, or fluffy in appearance. Their name derives from the Latin , meaning "heap" or "pile". Cumulus clouds are low-level clouds, generally less than in a ...

clouds, especially towering cumulus and

cumulonimbus Cumulonimbus () 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 va ...

. The vertical extent of a cumulus cloud is a good indicator of the strength of lift beneath it, and the potential for cloud suck. Cloud suck most commonly occurs in low pressure weather and in humid conditions. Cloud suck is typically associated with an increase in thermal updraft velocity near

cloud base A cloud base (or the base of the cloud) is the lowest altitude of the visible portion of a cloud. It is traditionally expressed either in metres or feet above mean sea level or above a planetary surface, or as the pressure level corresponding t ...

. As a parcel of air lifted in a thermal rises, it also cools, and water vapour will eventually condense to form a cloud if the parcel rises above the

lifted condensation level The lifting condensation level or lifted condensation level (LCL) is the height at which the relative humidity (RH) of an air parcel will reach 100% with respect to liquid water when it is cooled by dry adiabatic lifting. The RH of air increases ...

. As the water vapour condenses, it releases its

latent heat of vaporization In thermodynamics, the enthalpy of vaporization (symbol ), also known as the (latent) heat of vaporization or heat of evaporation, is the amount of energy (enthalpy) that must be added to a liquid substance to transform a quantity of that sub ...

, thereby increasing the buoyancy of the parcel. The updraft is amplified by this latent heat release. Although the process that causes this amplification happens above cloud base height, the effect is often noticeable as much as 300 m (1,000 feet) below cloud base. In fact, it is this effect ''below'' cloud base, not the effect ''within'' the cloud, that is generally referred to by pilots as cloud suck. The telltale signs for a pilot climbing in the thermal under a "sucking" cloud are (1) lift strengthening, (2) lift getting smoother, and (3) widening of the thermal. Paraglider pilots have reported being unable to descend in strong cloud suck, even after bringing their canopies into deep spiral, which would normally result in a rapid vertical descent. Cloud suck is especially dangerous for paraglider pilots, whose maximum speed is less than 30 knots, because storm clouds (Cumulonimbus) can expand and develop rapidly over a large area with accompanying large areas of strong lift. Compared with hang-gliders and paragliders, sailplanes have much higher top speeds (often over 250 km/h), and can more easily escape powerful cumulonimbus clouds by flying away quickly or by using very effective air brakes. A sailplane also has the added benefit of the pilot being able to put the sailplane into a spin to descend rapidly without over speeding. Shenandoah Disaster

Cloud suck is also a concern for powered aircraft but is usually not a lethal hazard, except in extreme weather situations. The USS ''Shenandoah'', the first rigid

airship An airship, dirigible balloon or dirigible is a type of aerostat (lighter-than-air) aircraft that can navigate through the air flying powered aircraft, under its own power. Aerostats use buoyancy from a lifting gas that is less dense than the ...

built in the United States, and the first in the world to be inflated with

helium Helium (from ) is a chemical element; it has chemical symbol, symbol He and atomic number 2. It is a colorless, odorless, non-toxic, inert gas, inert, monatomic gas and the first in the noble gas group in the periodic table. Its boiling point is ...

, was lost in a cloud suck accident associated with 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 ...

. At about 6:00 AM on 3 September 1925, near Ava in northern

Noble County, Ohio Noble County is a county located in the southeastern part of the U.S. state of Ohio. As of the 2020 census, the population was 14,115, making it the fourth-least populous county in Ohio. Its county seat is Caldwell. The county is named for ...

, the ''Shenandoah'' was suddenly caught in a violent updraft while at an altitude of , rising at the rate of a meter per second. At about the ascent was checked, but the ship began to descend. When halfway to the ground it was hit by another updraft and began to rise rapidly at an even faster rate. Ultimately the keel snapped, and the ship broke up while still more than a mile above the ground. ''Shenandoah'''s commanding officer and 13 other officers and men were killed. Twenty-nine members of the crew survived the break-up, although some received serious injuries.

Reported incidences

On 14 February 2007 while practising for a paragliding contest in Australia, Polish-born German team pilot Ewa Wiśnierska-Cieślewicz was sucked into a cumulonimbus cloud, climbing at up to 20 m per second (4,000 feet per minute) to an altitude of 9,946 m (32,600 feet). She lost consciousness due to hypoxia, but regained consciousness after 30 minutes to an hour, and landed still covered in ice after a three and a half hour flight. In the same storm, 42-year-old Chinese paraglider pilot He Zhongpin died after being sucked into the same storm system and struck by lightning at 5900 m (19,000 feet). His body was found the next day from his last known position prior to entering the cloud. In 2014 Italian paraglider Paolo Antoniazzi, a 66-year-old retired Army general, died after being sucked into a thunderstorm. In 2025 Chinese paraglider Peng Yujiang was lifted 5000m into the air to an elevation of 8000m whilst testing the fit and comfort of his parachute on the ground.{{cite web, url=https://www.bbc.co.uk/news/articles/cm238175gzyo, title=China: Paraglider survives accidental 8000m-high flight, date=29 May 2025

References

{{Reflist, 2

External links

* Steve Roti
How to Avoid Cloud Suck
article on USHPA website, first published in Paragliding Magazine, January 2001 Cloud and fog physics Gliding technology Hang gliding Paragliding Weather hazards to aircraft

Reported incidences

See also

References

External links