Placeholder to add my progress on the "tweaks" to BuckeyeBob's cloud MOD. Thanks to BuckeyeBob for the head start and help.

OrbyxP, I am willing to work together with you on this, if you wish. I already have a spreadsheet for every day of the war with the weather information that I have on hand. Looking at your data, it looks remarkably similar to mine. The main difference is, as you said, that many flights were cancelled due to factors other than rain, and that your records indicate that some periods went for a very long time without any flying whatsoever, due to any number of reasons (rain, fog, wind).

I can send you my spreadsheet, it you want. Send me a PM, where we can discuss this further.

Indeed. I've browsed squadron diaries of French units (journal des marches et opérations) many times and it is obvious that they were simply not flying during bad weather. And in the case of very precise missions, the very few pilots who took to the air generally did not show any other aerial activity in their mission reports.

Update:

BB has been busy and generous enough to incorporate my data into his excellent weather mod. 1916 is in beta testing by me but I assume that it would be ok for others to test, too if BB doesn't mind.

There are a lot of similarities between BBs data and the RFC communique.The main differences are a bit more days with precipitation and fog/haze in the official records. Low clouds were also very prevalent and a hindrance for any observation work. It is very obvious from the weather data that mother nature played a big role and dictated when to fly.