It is in Chapter Eleven when Jonas receives the memory of somebody sledging down a hill in snow. He is completely perplexed by snow, as he has never seen it before and is transfixed by the white powder that is all around him and which continues to fall. After the memory has finished, he asks the Giver why it is that they do not have snow in their own world, curious as to why his present is so different from the past of humans that he is now able to experience through the memories he is being shown. Note the explanation that the Giver supplies him:
Climate Control. Snow made growing food difficult, limited the agricultural periods. And unpredictable weather made transportation almost impossible at times. It wasn't a practical thing, so it became obsolete when we went to Sameness.
In this technologically superior world, the weather is something that can be completely controlled and manipulated according to the wishes of man. This is why Jonas has never seen snow before in his life: it has not snowed in this future world for a very long time now. The way in which the weather is controlled so strictly is of course a symbol of the strict control that characterises this society, and also its lack of freedom.
The reason is the community took everything memory of color, snow, etc. Away taking their rights. So he does not know what snow is until he received the memory.