If you live anywhere remotely cold, you have experienced one thing snow. With snow comes many things, terrible driving, ice, shoveling driveways, all not fun things. But if you have ever taken a walk through the woods on a snowy day, you will recognize one thing, or rather a lack of one thing, sound.
The reason why it becomes so quiet when there is snow on the ground is due to the physical shape of a snow flake. Because there are so many snowflakes on the ground, there is a lot of empty space between them. This large amount of space causes the snow on the ground to be a very good sound insulator.
To test this out next time there is snow on the ground, grab a friend, go outside and stick your head under the snow and yell. Your friend can then observe how muffled your sound becomes.