here is a WIP I am working on (with a trainee) to generate sky appearance in real time that we will soon use in our game.
note that it is still a WIP : some problems still appears in rendering and it is not yet fully optimized.
for each frame the Applet generate the five skybox texture, apply them to a skybox & render the frame
What you cannot see online :
The current version enable to set a location on earth and a date to generate the sky with the correct sun location ( it should also soon put the correct clouds coverage of the selected area)
It can also generate the sky reflection map texture ( the one you may apply on reflective object : chrome/sea/etc...)