I think alot of the mathematical and actual coding work has been done, you can see hints of it in the FMB. There is what appears to be a weather map overlay option although it doesn't do anything and there is also a weather menu with a flow and wind generator.
At the moment all you can really do is choose from 3 generic cloud cover types and set the height which is a shame but this is one of the key reasons the graphics engine is getting its overhaul is so they get the overhead to add more complex systems in.
