Definition
A large, fairly well-defined mass of clouds seen at a distance, covering a portion of the sky on the horizon but not directly overhead.
Plain English
A thick wall or pile of clouds that you can see off in the distance, usually low on the horizon, with clearer sky above and around it.
Context Anchor
Seen in weather reports, pilot weather briefings, and out the windshield when a large area of cloud lies ahead or along the horizon.
Derivation
‘Bank’ here comes from the older sense of the word meaning a raised mass or ridge — the same sense used in ‘snow bank’ or ‘bank of earth.’ A cloud bank is a raised, piled-up mass of cloud, distinct from the surrounding sky.
Why Pilots Care
Signals possible loss of visual references, turbulence, or need to change route to stay in VFR conditions.
Grounding Statement
Picture flying toward a long white or gray wall across part of the sky; that wall-like cloud mass is a cloud bank.
Intuition Check
“Bank” does not mean a turn of the airplane here. It means a large, connected mass or wall-like group of clouds.
Example Sentence 1
On climb-out, the pilot noticed a thick cloud bank building to the west and decided to check the latest weather before continuing.
Example Sentence 2
As we neared the cloud bank the ceiling dropped and we requested an IFR clearance.