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Fractus clouds (''scuds'') also known as Fractostratus or Fracto-Cumulus are small, ragged
Fractus are accessory clouds, named for the type of cloud from which they were sheared. The two principal forms are cumulus fractus (formerly, fractocumulus) and stratus fractus (formerly, fractostratus). Fractus clouds may develop into NOAA Cloud Types
- NOAA Chart of Different Cloud Types. Observing fractus gives an indication of wind movements under the parent cloud. Masses of multiple fractus clouds, located under a main cloud, are called pannus. Fractonimbus are a form of stratus fractus, developing under precipitation clouds due to turbulent air movement. They are dark-gray and ragged in appearance. Fractonimbus exist only under precipitation clouds (such as nimbostratus, altostratus or
In rainstorms, scud often form in the updraft area where the air has been cooled by precipitation from the
Fractus clouds (''scuds'') also known as Fractostratus or Fracto-Cumulus are small, ragged cloud
In meteorology, a cloud is an aerosol consisting of a visible mass of miniature liquid droplets, frozen crystals, or other particles suspended in the atmosphere of a planetary body or similar space. Water or various other chemicals may ...
fragments that are usually found under an ambient 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 to ...
. They form or have broken off from a larger cloud, and are generally sheared by strong wind
Wind is the natural movement of air or other gases relative to a planet's surface. Winds occur on a range of scales, from thunderstorm flows lasting tens of minutes, to local breezes generated by heating of land surfaces and lasting a few ...
s, giving them a jagged, shredded appearance. Fractus have irregular patterns, appearing much like torn pieces of cotton candy
Cotton candy, also known as fairy floss and candy floss, is a spun sugar confection that resembles cotton. It usually contains small amounts of flavoring or food coloring.
It is made by heating and liquefying sugar, and spinning it centri ...
. They change constantly, often forming and dissipating rapidly. They do not have clearly defined bases. Sometimes they are persistent and form very near the surface. Common kinds include ''scud
A Scud missile is one of a series of tactical ballistic missiles developed by the Soviet Union during the Cold War. It was exported widely to both Second and Third World countries. The term comes from the NATO reporting name attached to the mis ...
'' and ''cloud tags''.
Forms
Fractus are accessory clouds, named for the type of cloud from which they were sheared. The two principal forms are cumulus fractus (formerly, fractocumulus) and stratus fractus (formerly, fractostratus). Fractus clouds may develop into cumulus
Cumulus clouds are clouds which have flat bases and are often described as "puffy", "cotton-like" or "fluffy" in appearance. Their name derives from the Latin ''cumulo-'', meaning ''heap'' or ''pile''. Cumulus clouds are low-level clouds, gener ...
if the ground heats enough to start convection
Convection is single or multiphase fluid flow that occurs spontaneously due to the combined effects of material property heterogeneity and body forces on a fluid, most commonly density and gravity (see buoyancy). When the cause of the c ...
. Stratus fractus is distinguishable from cumulus fractus by its smaller vertical extent, darker color, and by the greater dispersion of its particles.
Cumulus fractus clouds actually look like ragged cumulus clouds. They may originate from dissipated cumulus clouds, appearing in this case as white ragged clouds located at significant distances from each other. Cumulus fractus in particular form on the leading and trailing edges of summer storms in warm and humid conditions.- NOAA Chart of Different Cloud Types. Observing fractus gives an indication of wind movements under the parent cloud. Masses of multiple fractus clouds, located under a main cloud, are called pannus. Fractonimbus are a form of stratus fractus, developing under precipitation clouds due to turbulent air movement. They are dark-gray and ragged in appearance. Fractonimbus exist only under precipitation clouds (such as nimbostratus, altostratus or
cumulonimbus
Cumulonimbus (from Latin ''cumulus'', "heaped" and ''nimbus'', "rainstorm") 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. ...
), and don't produce precipitation themselves. Fractonimbus may eventually merge completely with overlying nimbostratus clouds.
Significance in thunderstorms
In rainstorms, scud often form in the updraft area where the air has been cooled by precipitation from the downdraft
In meteorology, an updraft is a small-scale current of rising air, often within a cloud.
Overview
Localized regions of warm or cool air will exhibit vertical movement. A mass of warm air will typically be less dense than the surrounding regi ...
, thus condensation occurs below the ambient cloud deck. If scud are rising and moving towards the main updraft, sometimes marked by a rain-free base (RFB) or wall cloud
A wall cloud (murus or pedestal cloud) is a large, localized, persistent, and often abrupt lowering of cloud that develops beneath the surrounding base of a cumulonimbus cloud and from which tornadoes sometimes form. It is typically beneath the r ...
, then the thunderstorm is still developing from rising scud.
In addition to forming in inflow, fractus also form in outflow. Scud are very common on the leading edge of a thunderstorm where warm, moist air is lifted by the gust front. Scud are usually found under shelf clouds.
See also
* List of cloud typesReferences
{{Cloud types Accessory clouds