Cold air is denser, so the molecules are more closely packed together. What makes it denser is that the molecules aren't moving around and bouncing into each other as much, so each molecule occupies a smaller average volume of space. Because sound is transmitted by molecules colliding into each other -- and more collisions occur in warm air than in cold air -- the speed of sound is higher in warm air than in cold air. What you learned about cold air sound wave travel in your grunthood (is that a word?) is not always true.

Sound will reflect and refract off of air temperature gradients. If the air is still sound will travel further than if the wind is blowing, not because the wind interrupts the sound wave directly, but because there are more temperature gradients between the source and the listener.

If there is a layer of air a distance above ground that is cooler than the air at ground level -- as is often the case in the afternoon -- the speed of sound decreases with height. This means that a sound wave traveling close to the ground is traveling the fastest, and the part of the wave farthest above the ground is traveling the slowest. This effect tends to pull or bend the wave upward away from the ground.

If the air is coolest at ground level and warmer layer exists above it -- as is often the case on a cold morning soon after sunrise -- sound waves would be refracted down and have a chance of bouncing back and forth between the ground and the cold layer above it to reach much further than is normally possible.

I can explain it to you but I can't understand it for you.