'Creating a 'Snowstorm' Effect'

Clive R. Haynes FRPS

Open the Image as a 'Background'
Make a new (empty) layer above the Background layer

Fill with 50% Gray via Edit > Fill > Use 50% Gray > OK
The image layer fills with Grey

Go to Filter > Noise > Add Noise
Choose 'Gaussian' and 'Monochromatic' settings
For the 'Amount' put in between 200% and 280%
Click OK

The screen is now a 'storm' of black & white 'noise'.
The white parts will become our 'snowflakes'.

Use the Magic Wand to select the 'white noise' pixels.
To make this simple, zoom in to a large magnification, say 800% to 1600% and click on a white pixel, 'marching ants' appear as a 'mesh' all over the image.

Note: The Magic Wand tool options should be set for:
Tolerance 0 (zero)
Anti-Aliased - off
Contiguous - off

In addition, the Eyedropper Tool; should be set for 'Point Sample'. If the Eyedropper option is set to '3 x 3 average' or '5 x 5 average' the individual white pixels will not be selected, instead the entire image area will be selected.

To continue:
Select > Modify Selection
Contract by 1 pixel
OK

Select > Modify Selection
Expand by 1pxl or 2pxls
OK

Inverse Selection by Select > Inverse Selection (Ctrl + Shift + I)

Press 'Delete' to remove the unwanted pixels

Inverse Selection again by Select > Inverse Selection (Ctrl + Shift + I) to activate the required pixels

Option:
Save the Selection by Select > Save Selection
Name it 'Snow Medium'
This is an option that allows a return to the selection.
It's useful for making additional layers of 'snow' which can be 'fine' or 'heavy' depending upon how the selection is modified by 'contract' or 'expand'.

To continue:
Create a new (empty) layer above the Gray / Noise layer

Edit > Fill > Use > White
OK
Deselect via Select > Deselect (Ctrl + D)

Turn off the Gray / Noise layer (it's done its job)

Static 'snow flakes' now fill the image area.

Motion Blur can be applied to give an amount of movement.
Go to Filter > Blur > Motion Blur and adjust both 'Angle' and 'Distance' to suit.
Adjust the opacity of the 'snow' layer to best effect.

Apply a Layer Mask to the 'snow' layer to selectively erase areas as required.

Refinements:

Create a new layer and load the 'Snow Medium' selection saved earlier.
Expand the selection slightly to make larger 'flakes'.

NB. Sometimes expanding the selection can be problematical as expanding by as little as 1 pixel can result in the whole area being 'selected' as the 'snowflakes' join up!
Expanding can also make the snow too dense.
Should either be a problem, go to the alternative methods described below.

To continue:
Fill with white and Deselect.
Apply Motion Blur as appropriate (choose a different amount)

To make smaller 'flakes'
See below

NB. Remember to create a new layer for each density of snowfall

Alternative methods for Snowflake size
An alternative method for creating larger and smaller snowflakes it to use Edit > Transform > Scale facility. Begin with the 'static snowflakes'.
For larger flakes simply transform and enlarge to suit.

For smaller snowflakes
Transform the 'static snowflakes' to a reduced size
Turn off all layers except for the 'Static Snowflake' layer (as the 'Pattern' will be created from all 'visible layers') Select an area (must be a square-cornered non-feathered selection) then use Edit > Define Pattern, name it and click OK.
Load the pattern to a new layer via Edit > Fill > Use > Pattern (just made)
The 'snowflake' pattern appears
Use the 'Clone' tool to fill in the gaps in the tile pattern created.

Use 'Motion Blur' as described earlier

To create some really large snowflakes, try using the 'Rough Round Bristle' brush in the CS brushes list (about four-up from the base of the list it's preset to 100). Use the square bracket keys [ and ] to enlarge the brush size and with white as the foreground colour, apply with a 'dabbing' motion to apply to a separate layer.

Experiment with different 'Blend Modes' for the 'Snow Layers'.
Try 'Dissolve' blend - creates a 'sparkle' effect with reduced layer opacity.

It's a good idea to create a 'Layer Set' for the Snow Layers. This will tidy them away and to enable a Layer Mask to be added to the whole set if required.

To create a Layer Set, link the Snow Layers using the 'Link' icon and with the fly-out layer menu (top RH of layer palette), choose 'New Set from Linked'.

Remember, the process described above is very dependent upon file size and a great deal of experimentation is required to refine the technique for an individual image.

I have presented a 'working starting point' - have lots of fun in the snow!