When the last snow fell I picked some up and put it in the freezer, sealed in a plastic bag to keep moisture out. I hoped I'd be able to get it out in the summer and throw a snowball at someone on the hottest day of the year. It didn't work. After a few months in the freezer the snow turned to ice, and throwing a lump of ice at somebody isn't funny. Basically I'd like to be able to preserve a handful of snow from January until June, and be able to get it out again in the same fluffy condition it was in when I picked it up. How can I achieve this? What physical processes are responsible for turning the snow to ice? I thought I'd protected it against moisture from the air, by sealing the snow in a plastic "zip lock" bag. Maybe my freezer isn't cold enough? How cold does it need to be?