Convection mid-level.

The convection base lies clearly above the cloud base height. The convective layer is rather narrow, with a depth usually up to about 2 km. Convection often appears within or beneath the mid-level cloud layer, so it is not a “clean cumulus” sky.

What it means for flying: Near the ground, thermals may be weaker or only work locally, for example in sunny gaps, near cloud edges, or on hill slopes, and they are harder to read from cumulus clouds. More active air may appear at higher levels.