Mid-Level Clouds

Mid-level clouds(Family B) include Altostratus and Altocumulus cloud types.
Altostratus clouds form when a rising air mass condenses when in contact with a weather front.
They are often thin and allow sunlight through.They form in a layer.
Altocumulus clouds form the same way as Altostratus do but in a different appearance.
They are thicker in altitude and do not allow light through.Both cloud types can cover thousands of square kilometres.
Altostratus

(eo.edcar.edu)

Altocumulus

(wikipedia)

Different Types of Clouds

Clouds are classified by their altitude, shape and name.
As seen in the video below there are three general categories of clouds;

1. High level clouds - 6'000m - 12'000m (20'000ft - 40'000ft)
                              - these include: Cirrus, Cirrostratus, Cirrocumulus

2. Mid-level clouds - 2'000m - 6'000m (6'500ft - 20'000ft)
                             - these include: Altostratus, Altocumulus

3. Low level clouds - 0m - 2'000m (0ft - 6'500ft)
                              - these include: Stratus, Nimbostratus, Stratocumulus