Make it snow in a certain area

How could I make it snow in a certain area which I define using wold edit?

 

Like TimTower mentions you can and should change the biome to allow the biome to be a biome that allows snow fall by default. (Not sure if you can force snow in a non-snow biome)
If you want just a small region in that biome to snow but not the rest you'll need to use WorldGuard regions. Make the whole snow-biome a (parent) region with snow-fall flag set to none. Then make a smaller region inside that region where you want it to snow and change that flag to snow-fall allow.
Edit: Don't forget to set the priority of the child-region (one with snow allow) to a value higher than the parent regions priority.
Link to WorldGuard Flags.

 

Okay thanks. Sounds complicated but thank you

 

ErraticServers

• /snow <radius>

 

I mean snow flakes falling from the sky. Not snow on the ground

 

ErraticServers Oh sorry, then yes, you should just change the biome.