http://www.npr.org/2015/10/02/444877155/whats-at-the-edge-of-a-cloud

They focused on the clouds' edges — where dry air is mixing in.
You might think all the droplets at the edge of a cloud would evaporate a little
bit and that they would all shrink. But that's not what happens.

Shaw says dry air seems to creep in and evaporate some droplets completely,
while others survive in wispy cloud filaments surrounded by clear air.

"The droplets that are remaining are just as big as the droplets that are in the
center — kind of the protected core of the cloud, where no evaporation has taken
place," he says. "That was a surprise to us."