Is it just me or does it get quieter outside when a couple of inches of snow are falling?
Actually, the answer is a combination of both.
First of all, during a big snowfall, there are likely to be less people and other noise making devices outside, so there is less initial sound hitting they eardrums, without regard to any effect the snow has on sound waves.
What if the amount of noise made is the same before a snowfall and during/after?
Sound waves are absorbed by porous and insulating materials. Freshly fallen snow has plenty of air pockets for sound waves to get trapped in. Regularly, sounds bounce off of hard surfaces like the ground before they reach the ear, so when the snow insulates these sounds, the angles from which sounds reach the ear are greatly reduced.
The temperature during snowfall compared to a warm clear day is also a factor. Lower temperatures slow down sound waves, and sound waves, like other types of waves, refract when they change speed. During the winter, when the ground is cold, and the air is warmer, like during a clear winter day, sound waves refract down when hitting the lower colder air, making more opportunities for sound reflection.
During snowfall, the air is relatively as cold/colder than the ground, causing the opposite effect, leaving less opportunities for sound reflection, and sound get carried into the atmosphere.
Enjoy the quiet winter days/nights!