Definition
Extensive accumulations of visible water droplets or ice crystals suspended in the atmosphere, covering a wide horizontal or vertical extent. In the thunderstorm context, the phrase refers to the towering, broad cloud structures associated with convective weather, where individual cells and surrounding cloud cover can hide hazardous conditions such as turbulence, hail, lightning, and embedded storms.
Plain English
Big areas of cloud that take up a lot of sky. They can hide dangerous weather inside them, especially around thunderstorms.
Context Anchor
Seen in weather decision-making, especially when a pilot is trying to avoid thunderstorms during instrument flight or while flying near areas of poor visibility.
Why Pilots Care
These formations contain turbulence, icing, lightning, and strong vertical air currents that can damage aircraft or cause loss of control.
Grounding Statement
From the cockpit, a large cloud mass may look like one continuous wall of cloud, even though the dangerous weather may be hidden inside it or behind it.
Intuition Check
Do not read this as simply “big clouds are always storms.” In this context, the point is that large cloud areas can conceal thunderstorm hazards and deserve extra caution.
Example Sentence 1
The pilot diverted around the large cloud masses building to the west rather than risk an inadvertent thunderstorm encounter.
Example Sentence 2
ATC advised deviating around large cloud masses reported along the arrival route.