[Ammi]

…the first explanation that comes up on Googling….

When it's cold, sounds can travel further and seem different because the air is denser and causes sound waves to bend back toward the ground, a phenomenon amplified by the stillness of the air. This is known as a temperature inversion, where cold, dense air sits below warmer air, creating a layering effect that acts like a lid, trapping sound and allowing it to be heard more clearly and for longer distances.