This is neat. We've deployed a 98+% accuracy satellite & aerial cloud detection solution for many years, so I would have the following suggestions:

-Why use AlexNet and not VGG (or Googlenet)?

-Make sure to train on clouds vs desert. There are a lot of instances where their spectral signatures are very close, depending on the satellite.

-Make sure to train on clouds vs snow. They are even more close.

-Dark clouds. This might not show up much unless you're working with the satellite vendor, but there are cloud formations where shadows of clouds project onto other clouds. Very difficult to deal with and NN may be well suited to it.

I would say since it's absolutely possible to get higher accuracy using older methods on this exact satellite constellation, there is definitely room for improvement. Just switching to VGG might even do the trick. But this is a great first step!