Some parts of the new weather engine are included "as is" in the "Full Mission Builder" and can be used (at your own risk
).
The module is still buggy, the rain isn't working, the GUI is a mess and can crash in a heart bit, but is fun to experiment with it.
You can try it for yourself. The "Local Weather" tab in the object list gives you access to few things. Play with them and see what you can do.
I can't wait for that part of the game, together with the new clouds to be included in the sim. To me the clouds and sky make the flying such a unic form of travel, and a flying sim should pay top priority to the things that make flying so beautiful.