Altocumulus castellanus cloud
Encyclopedia
Altocumulus Castellanus is named for its tower-like projections that billow upwards from the base of the cloud. The base of the cloud can form as low as 2,000 metres (6,500 feet), or as high as 6,000 metres (20,000 feet).
Castellanus clouds are evidence of mid-atmospheric instability and a high mid-altitude lapse rate
. They may be a harbinger of heavy showers and thunderstorms and, if surface-based convection
can connect to the mid-tropospheric
unstable layer, continued development of Castellanus clouds can produce cumulonimbus
clouds.
Altocumulus Castellanus clouds are typically accompanied by moderate turbulence
as well as potential icing
conditions. For these reasons, flight through Altocumulus Castellanus clouds is often best avoided by aircraft.
The appearance of Altocumulus Castellanus early in a sunny day may indicate a high probability the formation of thunderstorms in the afternoon, as they may develop into cumulonimbus storm clouds.
Castellanus clouds are evidence of mid-atmospheric instability and a high mid-altitude lapse rate
Lapse rate
The lapse rate is defined as the rate of decrease with height for an atmospheric variable. The variable involved is temperature unless specified otherwise. The terminology arises from the word lapse in the sense of a decrease or decline; thus, the lapse rate is the rate of decrease with height and...
. They may be a harbinger of heavy showers and thunderstorms and, if surface-based convection
Convection
Convection is the movement of molecules within fluids and rheids. It cannot take place in solids, since neither bulk current flows nor significant diffusion can take place in solids....
can connect to the mid-tropospheric
Troposphere
The troposphere is the lowest portion of Earth's atmosphere. It contains approximately 80% of the atmosphere's mass and 99% of its water vapor and aerosols....
unstable layer, continued development of Castellanus clouds can produce cumulonimbus
Cumulonimbus cloud
Cumulonimbus is a towering vertical cloud that is very tall, dense, and involved in thunderstorms and other inclement weather. Cumulonimbus originates from Latin: Cumulus "Heap" and nimbus "rain". It is a result of atmospheric instability. These clouds can form alone, in clusters, or along a cold...
clouds.
Altocumulus Castellanus clouds are typically accompanied by moderate turbulence
Turbulence
In fluid dynamics, turbulence or turbulent flow is a flow regime characterized by chaotic and stochastic property changes. This includes low momentum diffusion, high momentum convection, and rapid variation of pressure and velocity in space and time...
as well as potential icing
Icing
Icing may refer to:* Atmospheric icing, occurs when water droplets freeze on objects they contact, very dangerous for aircraft* Aufeis, also called icing, a sheet-like mass of layered ice that forms from the freezing of successive flows of groundwater...
conditions. For these reasons, flight through Altocumulus Castellanus clouds is often best avoided by aircraft.
The appearance of Altocumulus Castellanus early in a sunny day may indicate a high probability the formation of thunderstorms in the afternoon, as they may develop into cumulonimbus storm clouds.