Altocumulus castellanus

(Section 2.5.2.4.4)

This Altocumulus has cumuliform tops rising from a common base.

Below the cloud. Viewed from below, this cloud has a horizontal and fairly extensive base, resembling a layer of Altocumulus. Just below the cloud, visibility is reduced by haze, and virga may fall from the cloud. Turbulence increases near the base.

Within the cloud. Within the higher towers of the upper part of this cloud, turbulence is generally strong, and electrical discharges (Saint Elmo’s fire) may be observed. Visibility is variable, and icing may occur.

Above the cloud. Viewed from above, this cloud strongly resembles well-developed Cumulus clouds with their bases buried in a haze layer or a smooth and wavy cloud layer. The vertical extent of the cumuliform towers varies. Some may develop into Cumulus congestus or even into Cumulonimbus, resulting in thunderstorms at high altitudes.