Sound carries further on cold nights
The usual explanation, that cold air carries sound better, is wrong in the direction people mean. Sound travels slightly slower in cold air, and attenuation is not dramatically different. What changes is the path.
On a clear calm night with a temperature inversion, air near the ground is colder than air above. Sound moves faster in the warmer air aloft, so wavefronts heading upward are bent back down. Energy that would have escaped into the sky is instead refracted toward the ground and returned, sometimes repeatedly. A source that would fade within a few hundred metres in a well-mixed afternoon atmosphere can stay audible for kilometres.
Wind does something similar but asymmetrically. Wind speed increases with height, so sound going downwind is refracted down and sound going upwind is refracted up, leaving an acoustic shadow upwind. This is why a distant road is loud on one night and inaudible on another with no change in traffic.
Snow cover complicates it by absorbing rather than reflecting, which reduces ground bounce. The net effect on a calm inverted night is still usually more range, not less.