Flat-bottomed clouds

[GalvestonDuck]

Can you explain what makes some cumulus clouds appear as though they are sitting on top of a glass shelf? Sometimes I've noticed how they all appear to be at the same level, like God covered us with an upside-down glass bucket and plopped dollops of cotton candy over our heads -- big, poofy white fluff blobs that a flat on the bottoms. I asked this once a long time ago (not here) and got some round-about answer concerning water vapor, but it wasn't clear enough for me to understand and I've had other people ask me. I'm sure they stop and rest at some atmospheric level, but I don't get why.

Thanks!

[Wthrman13]

Ah, excellent question.

The short answer is that the flat bottom of the clouds represents the LCL, or the lifting condensation level. Basically this is the level in the atmosphere where a parcel of air, lifted from the surface, first cools off enough for the water vapor to condense into cloud droplets. It just so happens that over relatively homogeneous terrain, the LCL is about the same or changes slowly over a large horizontal area. The visual effect is that the clouds all appear to have a flat base at about the same level.

[GalvestonDuck]

Very cool! Thanks again!