A sub-type of Altocumulus clouds.
These altocoumulus have a cumulus-like look to them, just that they are higher up (cloud bases between 2000 and 5000m). Altocumulus Castellanus is an altocumulus with a tower. It shows that the air is instable.
© M.I.L.K. 2017
M.I.L.K. - Meteorology: Information. Learning. Knowledge.