Rain Shadow is basically done and scaled to a setting.
The top image has a setting of 5, and the bottom is maxed at 9:
An Earth-Like setting will probably be somewhere between 6 and 8.
Right now the Rain Shadow works only with mountains. I may alter it somewhat to instead work on the heightmap which should allow for a full rain shadow without also requiring a full, un-eroded line of mountains.
I will see if I can work out the jet streams tomorrow, and maybe the seeding.