Hi zBrush experts, I need your knowledge to solve a problem I have at the moment. 
I have a scene with a bunch of trees, and I want to add on top of them a layer of snow, something like this:
Basically, what I want to do, is to sculpt new geometry over my trees, but only in the areas exposed on top, to simulate the deposit of the snow.
Any Ideas on how can I do that without manually sculpt and paint the snow on every branch of every tree? 
Lots of ways to do this. Not many good ones that donât involve sculpting or painting. Zbrush is a sculpting and painting application.
One way would be to make use of Zketching. You can Zsketch a layer of Zpheres over the tops of the limbs where you want snow, which will then be âskinnedâ into a mass on top of the limbs which can be further shaped at higher resolution.
Perhaps a better way, would be to mask out the portions of the geometry where you want snow, and use the âExtractâ function in the Subtool menu to extract a mass that conforms to the shape of the limb for further sculpting.
Perhaps a combination of the two would be best, extract the major bodies of snow, use zsketching to pepper smaller little accumulations here and there and along the edges of the snow masses. I would also paint the underlying limbs with some white noise along the edges of the snow maasses to diffuse their shape, and represent snow particles too small to model.
Brushes like Form Soft and Inflate will be helpful for establishing the proper form. Dynamesh will be helpful to pull down icicles with the move and snakehook brush.
From there, if you were creating the image in Zbrush, you could make use of Zbrushes new Wax and SSS material effects to give the snow a sort of translucent quality. (See the new vids in the Zbrush classroom).
Anything you do will require manual painting or sculpting on some level, if you want the best results.
Thanks to state the obvious 
I didnât mean to do it in one click, I just want to know the best or more efficient way to do it! 
So, can you tell me some of this many ways?
Sorry, I had a twitchy âsubmitâ finger, and you posted before I could edit in my suggestions.
Thanks a lot Spyndel, I will try what you suggested. 
I would look at using Backface Masking, with the drag rectangle stroke on your masking brush. With this you can drag out a mask across the whole tree viewed from directly above, to isolate only the surfaces that point to the sky.
With just the area where you want snow unmasked you can then apply an Inflate deformation and then add a bit of noise.
Couldnât you just make a copy of the tree and make it âsnow coloredâ and move it up slightly?
Hit âDuplicateâ in the Subtool Pallet,
Select the new tree in the Sub
then in the Deformaition pallet set âOffsetâ to Y and try slowly moving it up, maybe by typing in the number field.
Also maybe (if that worked) try using âInflate Balooonâ to get that slight overhang snow would have.
Cheers!
Mealea
EDIT: I tried it out, very simple and under a minuet to make:
