Often, cumulus humilis represents an early stage in the development of a cumulus cloud from stratocumulus to cumulus mediocris and then cumulus congestus. Since it is also evidence of a high-speed, high-level wind, it may indicate the presence of a jet stream. Castellanus generally occurs when a layer of colder air slides across an area of altocumulus cloud. These clouds are essentially above-ground fog formed either through the lifting of morning fog or through cold air moving at low altitudes over a region. The time of day may be a deciding factor, as convection One dramatic form of Three types: Has an altitude of 500-3000 m (1,500-10,000 ft) with little vertical extent that is commonly referred to as "fair weather cumulus" and common in the summer. Stratus is the lowest altitude cloud formation, with over land weakens late in the afternoon when ground temperatures begin to fall. blowing at right angles to a steep mountain will create greater uplift and generate more cloud. In the absence of cloud, the same process can be a major source of clear air turbulence at high levels. Cirrus Fibratus: These are thin and fibrous and often can showcase the direction of high altitude winds which push the clouds in a certain direction leading to white parallel stripes streaking across the sky. by the humidity of the surrounding air mass. Earth's outer atmosphere. The extent of the cloud is also determined by the steepness and elevation of the landfornn, the strength of the wind, and the direction of the wind relative to the landform. Since cirrus clouds arrive in advance of the frontal system or tropical cyclone, it indicates that weather conditions may soon deteriorate because of atmospheric stability. In this case, the clouds may subsequently develop into cumulus Fortunately, because of the precipitation generated, the cloud is easily located by onboard and ground-based radar, and elaborate procedures are in place to steer aircraft around any such activity. (adsbygoogle = window.adsbygoogle || []).push({}); Cirrus Clouds on Sunset in Florida via JSJ Photography, Cirrus Clouds (Uncinus) over North Brisbane via HSC Admin Thomas, Public or Media enquiries: [email protected] the calvus cloud continues to rise, it gradually catches up with the pileus cloud. This produces clouds that generally have flat bases and small, rounded tops. word for layer) and occur when relatively large areas of moist air rise gently in a stable atmosphere to a level where Hazard Warning: Can be an aviation hazard as it sometimes masks terrain. Associated Weather: If extensive, may indicate an approaching frontal system; may also be a sign of a decayed thunderstorm. The second process involves pockets of warm air rising from the ground as a result of weak convection, giving rise to condensation at the same level over a wide area. of 20 to 30 miles per hour directly upward are possible -- a rather curious phenomenon may take place. Cirrus tends to be wispy and are mostly transparent or translucent. Sometimes, there is insufficient moisture in the lower layers of the atmosphere to allow condensation at ground level, but with increasing altitude and lower temperatures, condensation may be possible. It can, however, give rise to turbulence during aircraft penetration of the cloud, but this effect is normally slight and short lived. are usually hidden by the smoke from the wildfire, but the cloud tops are normally situated well above the smokescreen. Are as wide as they are tall. out over hundreds of square miles, the center of the storm Altocumulus formations are often more distinct and dramatic at sunrise and sunset. turbulence, and commercial airliners will try to avoid such Associated Weather: Light rain or snow; high winds. Since low-level moisture and high land are essential ingredients in the formation of orographic stratus, areas that have high humidity and steep terrain -- tropical islands such as Hawaii, for example -- are particularly conducive to the formation of these clouds. For the weather- As the crystals descend under the influence of gravity, this wind rapidly smears them across the sky, forming the distinctive, elongated, hooked shapes. Has an altitude of 500-3000 m (1,500-10,000 ft) and larger in vertical development than cumulus humilis. Cause: Lifting of a large air mass, followed by condensation combined with instability. Good examples occur when moist winds blow in off the Pacific Ocean and encounter the Sierra Nevada in California. the cloud is produced by wind shear, it is regarded as a sign of local turbulence. As long as the air in the vicinity of the updraft remains These clouds always indicate the presence of significant amounts of moisture at middle levels, and, if on the increase, may signal the or rain, or light snow in sub-zero temperatures, Among the most common are fibratus and nebulosis. This occurs when the temperature of the surrounding air mass drops more rapidly with height than is normal, often as a result of a cold air current sliding over the cloud. Strong wind The winds in these levels of the atmosphere can be constantly strong to very strong and its this wind shear that can morph and shape the clouds into different formations. significant in that it indicates instability in the middle layers of the atmosphere and may therefore point to thunderstorm development later in the day. Altocumulus lenticularis clouds are named for their smooth, round, lens-like shape (lenticular means lens or lentil-like). All rights reserved. produced by the lifting of a large, moist air mass, usually by an approaching cold front, combined with instability at cloud level. Associated Weather: Moderate to heavy showers, strong winds. This produces an Cirrostratus formations may cause slight turbulence at cloud level, but this is unlikely to affect aircraft operations or discomfort passengers. Because the formation is associated with mature cumulonimbus clouds, it is most likely to be seen from mid-afternoon to early evening, when ground heating and associated convective activity have reached a maximum. This variation of cumulus derives its name from the fact that fire (pyro in Latin) creates both the lifting mechanism and the water vapor that combine to form this cloud. Contrails also have a military and strategic significance in As with other undulatus forms, these ripples are produced An extensive wildfire produces vigorous rising air currents and a large quantity of water vapor that is released by the air and While light rain may fall, this cloud does not indicate much meteorological activity. source of uplift for the aircraft. A cumulonimbus incus formation must always be regarded as a significant aviation hazard because of the powerful air currents involved in its formation and the potentially damaging effect of the large hailstones it may produce.