In case it is of interest, this cloud detection thing ended up being weirdly useful.
As my goal is to create practical models for each fast.ai application,
I ended up negotiating with the Cloud Appreciation Society (https://cloudappreciationsociety.org/), training the model on their cloud dataset (over 150 000 clouds, probably largest in the world)
and we used the trained model to add a cloud detector in their Cloud-A-Day app ( https://play.google.com/store/apps/details?id=com.cloudappreciationsociety.cloudaday&hl=en).
The model (single-class 11 categories [10 main cloud types + not-a-cloud], resnet50) is now used daily in production by their members which are “over 46,000 members worldwide from 120 different countries, as of January 2019” which, as a lover of clouds of the physical type, I find pretty cool.
Thank you @jeremy I really appreciate the weird and wonderful things you and the fast.ai community are doing.