You will need : bicarbonate of soda
optional rock or stone
So first of all take your decorative rock or stone and PVA glue it to the gaming base of your choice!
Then you take your bicarbonate of soda!
Pour some PVA glue into a pot. A good dollop to start off with.
Then start adding small quantities of the soda powder. Add a couple of drops of white paint also at this stage. You are looking for a stodgy mixture that will stay on the end of your mixing tool.
Take a blob of the snow mixture and place it on your base. I find using my fingers works best here rather than using any tools. Don't worry everything will wash off your hands at the ends. Work the mixture around the rock in this case with your fingers until you achieve the look you want.
And there you go, as simple as that. A very easy snow base for you to put your miniatures on to and look great. A step further with these base is that you could put a very watered down blue wash over them and then maybe a glaze of varnish to give them a wet and slushy look.