Snow exercise part 1
1 Open snow1.jpg
2 Create a blank new layer
3 Edit > Fill...  - choose 50% Gray (from the drop down menu)
4 Change blending mode from Normal to Overlay
5 Filter > Noise > Add Noise... - about 85% (it won't work on empty layer)
6 Filter > Blur > Motion Blur... - 67 degree and 6 pixels
7 Image > Adjustments > Level and make adjustments to increase contras
8 Create blank new layer and drag it down in between the middle
9 Change the blending mode of new layer to Soft Light in order to paint with white
10 Select Brush Tool and start painting with white upper surfaces, imitating snow falling down
(this blending mode will only paint once, so don't worry about overpainting)
Snow exercise part 2
1 Open snow2.jpg, and using Move Tool, drug snow layer from previous image to the new one
2 Edit > Free Transform and stretch/adjust size of the layer (hold Shift key)
3 Create blank new layer and drag it down in between the middle
4 Change the blending mode of new layer to Soft Light
5 Select Brush Tool and start painting upper surfaces white, imitating snow falling down