Snowy days feel quiet because fresh snow is excellent at absorbing sound and everyday activity outdoors usually slows down.
Sound absorption by snow
A fresh, fluffy blanket of snow is made of many tiny ice crystals with lots of air pockets between them, which makes the surface very porous. When sound waves hit this porous layer, much of their energy gets trapped and scattered in those gaps instead of bouncing back, so sounds like cars, voices, and wind become noticeably muffled.
Effect of snow depth and type
The quiet effect is strongest when there are a few inches of light, newly fallen snow, because this type has the most open space to absorb sound. As snow compacts, melts, and refreezes into a harder, icier surface, those spaces close up and the surface starts reflecting sound again, so the world sounds less muted and can even seem louder.
Fewer noise sources
During heavy snow, there are usually fewer cars on the road, fewer people outside, and many animals become less active or take shelter. With less noise being produced in the first place, the already sound-absorbing environment makes the outdoors feel especially still and calm.
