Add Snow Effect to a Photo using Photoshop

1. Open Image in Photoshop (I'm using CS3)

2. Add New Layer & fill it with "Black" colour.

3. Go to "Filter ---> Noise ---> Add Noise..." .

4. Set values as below. (You can experiment with your own)

5. Go to "Filter ---> Blur ---> Blur More" .

6. Go to "Image ---> Adjustment ---> Levels..." .

7. Set values as below. (You can experiment with your own).

8. Change "Blend Mode" to "Screen".

9. Go to "Filter ---> Blur ---> Motion Blur..." .

10. Set values as below. (You can experiment with your own).

11. Duplicate the Layer (Right click on "Layer 1" & Duplicate Layer).

12. Go to "Edit ---> Transform ---> Rotate 180'" .

13. Go to "Filter ---> Pixelate ---> Crystallize..." .

14. Set values as below. (You can experiment with your own).

15. Go to "Filter ---> Blur ---> Motion Blur..." .

16. Set values as below. (You can experiment with your own).

17. Hold "Shift" and click on "Layer 1" & "Layer 1 Copy"  then use "Ctrl + E" to Merge layers(Blend mode should be "Screen").

18. Duplicate the Merged layer.

19. Lower the opacity of the top layer.

And here is the final outcome....

Source: photoshopessentials.com