Altocumulus castellanus
Ac cas
Altocumulus castellanus
© Wetterkurs.ch
Description
The name "castellanus" (Latin: castle-like, battlemented) describes the distinctive tower-shaped form of these clouds, reminiscent of the battlements of a medieval castle. Altocumulus castellanus appears as rows or groups of small cloud towers that grow upward from a common horizontal base. The vertical extent of the turrets clearly exceeds the width of their base. This cloud type forms through convective instability at mid-tropospheric levels, where moist air at altitude is prompted to rise. The individual turrets can change rapidly and often display a cauliflower-like structure at their tops, similar to small cumulus clouds.
Identification Features
- Tower-shaped or battlemented protrusions rising from a common flat base
- The height of the turrets is greater than their width
- Often arranged in lines or rows that follow the upper-level wind
- Cauliflower-like, cumulus-resembling tops at the peaks of the turrets
- Typically appear in the late morning or early afternoon hours
- The base lies in the middle level, usually between 2,000 and 6,000 meters
- Distinguished from Cirrocumulus castellanus by its larger elements and lower altitude
- The turrets can form and dissolve again within just a few minutes
Occurrence by genus
Highlighted: all genera with which castellanus occurs.
Meteorological Significance
Altocumulus castellanus is considered one of the most important harbingers of afternoon thunderstorms and convective severe weather. Its appearance in the morning indicates pronounced instability in the mid-troposphere, which favors the development of deep convection as the day progresses. In aviation meteorology, this cloud form is regarded as a significant warning signal, as it points to potential turbulence and thunderstorm development. Especially when Altocumulus castellanus appears in the early morning hours, the probability of severe thunderstorms in the afternoon is significantly increased. The rule of thumb "Castellanus in the morning, thunderstorms in the afternoon" is widespread and well-proven among meteorologists.
Facts
- WMO-Code
- Ac cas
- Height layer
- Mid-level clouds
- Typical height
- 2.0 - 6.0 km
- Genus
- ALTOCUMULUS