Fractus clouds over the Považský Inovec mountains.
Abbreviation St fr., Cu fr., Frnb Genus Cumulus or Stratus Species Fractus (broken) Appearance irregular, ragged Precipitation cloud? No, but may accompany precipitation clouds
Fractus clouds (scuds) are small, ragged cloud fragments that are usually found under an ambient cloud base. They form or have broken off from a larger cloud, and are generally sheared by strong winds, giving them a jagged, shredded appearance. Fractus have irregular patterns, appearing much like torn pieces of cotton candy. 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 and cloud tags.
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 if the ground heats enough to start convection. 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. 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), 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, 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, then the thunderstorm is still developing. Scud are common and are usually insignificant. However, scud precede wall clouds, which often form 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.
Cloud genuses Extreme-level High-level Medium-level Low-level Vertical
Wikimedia Foundation. 2010.
Look at other dictionaries:
Cloud — For other uses, see Cloud (disambiguation). Cumulus cloudscape over Swifts Creek, Australia A cloud … Wikipedia
Cloud species — are a set of fourteen tems used to describe the shape and structure of clouds. Each one has its name abbreviated to a three letter term. Cumulus Castellanus clouds Species Abbreviation Description Genera Calvus cal … Wikipedia
Cloud atlas — For other uses, see Cloud atlas (disambiguation). A cloud atlas is a pictorial key to the nomenclature of clouds. Early cloud atlases were an important element in the training of meteorologists and in weather forecasting, and the author of a 1923 … Wikipedia
Cloud condensation nuclei — Aerosol pollution over Northern India and Bangladesh NASA Cloud condensation nuclei or CCNs (also known as cloud seeds) are small particles typically 0.2 µm, or 1/100 th the size of a cloud droplet ) about which cloud droplets coalesce. Water… … Wikipedia
fractus — /frak teuhs/, adj. Meteorol. (of a cloud) containing small, individual elements that have a ragged appearance. [ < L fractus ptp. of frangere to BREAK] * * * … Universalium
fractus — /frak teuhs/, adj. Meteorol. (of a cloud) containing small, individual elements that have a ragged appearance. [ < L fractus ptp. of frangere to BREAK] … Useful english dictionary
fractus — noun a cloud species which consists of broken shreds of cloud, like scud. Associated with cumulus, and stratus genera. Source [ … Wiktionary
fractus — Clouds in the form of irregular and ragged shreds. The term applies to stratus and cumulus clouds. Fracto is used as a prefix for cloud forms to indicate that clouds are broken into irregular fragments … Aviation dictionary
List of cloud types — Clouds are formed in Earth s atmosphere when water evaporates into vapor from oceans, lakes, and ponds or by evapotranspiration over moist areas of Earth s land surface. The vapor rises up into colder areas of the atmosphere due to convective,… … Wikipedia
Cirrostratus cloud — Cirrostratus fibratus Abbreviation Cs Genus Cirrus curl of hair and stratus layered Alti … Wikipedia