Cool Nights Ahead!

Just like a water flowing down hill because it is pulled that way by gravity cool air is more dense than surrounding warmer air and it is pulled more by gravity than the warm, so ..... cool air will sink to the surface, flow down slope along the surface, pool in low spots and at times fill valleys.

Any experienced mountaineer or backpacker knows that most nights are warmer a ways up the slopes than at the bottom of the valley because of cold air drainage.

So at night cool air sinks and because the ground cools faster than the air the air is cooled even more by contact with the ground. This explains frost when your home thermometer, mounted at eye-level reads 35° - the cold air is hugging the ground.

Watch this video for more.