IFS Compose is a marvelous GIMP plugin by Oven Taylor. It might seen boring at the first time when you don't know what to with IFSC but after experimenting a while there are numerous possibilities to explore.
Create a new file with equal width and height and Black Background.
Adjust the foreground color to Light Gray. This will be used by IFS Compose as snow color at its initial run. You can ajust it later but it is easier to do it here.
Access IFS Compose by right clicking in the image : Filters/Render/Nature/IFS Compose (as in GIMP 1.1.28)
Click on New 4 times and arrange the shapes as shown below: one in center and 6 around the center.
You might do a little extra work to get the snow flake taste you actually need. Click on color transformation and adjust each hexagon's color so that they have slight variation and not all the same. It looks better if central hexagon is slightly lighter.
To play and create various snow flakes change the proportions of hexagons, rotate them so that all corners are at top.
I have created some snow brushes that can be found here.
