First, you need to pick a photo that will look natural once you add the snow to the shot. This tutorial works best with a shot that has a small covering of snow on the ground. Once you have a shot chosen, open it up in Photoshop.
Photo by Daniel Bell.
Create a new layer
To create our snow we need to make a new layer so go to Layer>New Layer or click the new layer icon in the layers palette. Rename this layer to 'Snow'.
Make a selection
Select the Rectangular Marquee tool and draw out a shape that's a 1/4 to 1/2 the size of the main image, making sure you have your new layer selected. You should now have a shape that's outlined with 'running ants' over your shot.
Fill your selection
Go to Edit>Fill and where it says 'Use' select black then click OK. Your shape should now be black, giving us a background to create our digital snow on.
Make it snow
To add snow go to Filter>Noise>Add Noise and set the Distribution to Gaussian and tick Monochromatic. To change the amount of snow that's in your shot, move the Amount slider to the left or right, depending on how much you want to add/ take away. A percentage between 30 and 100 will give anything from a light shower to a heavy blizzard. We've found less snow looks more realistic but do try various amounts to see what suits your image.
Adjust the snow
By going to Image>Adjustments>Threshold you can further increase or decrease the amount of snow falling in your shot. Threshold turns everything black or white and the slider controls how much is black and how much is white. Drag it to the left to increase the level of white and to the right to reduce it.
Make the snow fit
Go to Edit>Transform>Scale or Edit> Free Transform and drag the corners of the box so that it fills the whole image. You may be wondering why we just didn't fill the whole canvas with black in the first place and add noise to it but if we did this, the effect wouldn't work as well. By pulling the size of the canvas to make it fit the whole image changes the size of the white dots so they look less like noise and more like the snow we are trying to create.
Remove the black background
At the moment it looks like a night's sky rather than a snow scene and that' because we can't see the image underneath. To fix this, go the layers palette and from the blend mode menu change 'Normal' to 'Screen'. You should now be able to see your image through the snow.
We now have a scene covered in digital snow but it looks a little static so to add streaks to the snow so it looks like it's falling through the sky go to Filter>Blur>Motion Blur. Use the Angle to change the direction the snow is falling and adjust the Distance to add motion to the snow that's falling. Take care not to overdo this though as if you drag the slider too far to the right it can look like rain. If the Preview box is ticked you can see how the snow changes depending how much you adjust the distance and angle before you click OK.
If you still think the effect is a little too strong select the Erase tool, make sure you have a large sized brush and reduce the opacity to around 50% then brush over your image. This will remove some of the coverage, making the pattern more irregular.