Colloidal instability
From Glossary of Meteorology
colloidal instability
A property attributed to clouds (regarded in analogy to colloidal systems or aerosols) by virtue of which the particles of the cloud tend to aggregate (through Brownian motion) into masses large enough to precipitate.
The viewpoint that regards an atmospheric cloud as an aerosol somewhat strains the physical chemist's definition thereof, for cloud particles are much larger than the particles typically treated as colloidally dispersed materials either in a gas or in a liquid.