Turn any scene into a wonderland with a touch of noise and a Threshold adjustment.
Create a new layer. Go to Edit-Fill and select white from the use menu. Next go to Filter-Noise-Add Noise and set the distribution to Gausian and make sure Monochromatic is not enabled. Set amount to between 100% and 150%.
next activate Free-transform (ctrl+T) and increase the height and width to 150% - 200%.
Change the blending mode to screen then go to Image-Adjustments-Threshold. 200 is a good setting.
Go to Filter-Blur-Gaussian Blur and enter a radius between 0.5 and 1. to add the effects of movement go to Filter-Blur-Motion blur and adjust the angle to give a slant to the snowfall and set distance between 2 and 12. Finished.