Why is it colder just before the sun comes up?

It is simply colder just before the sun comes up because of the atmospheres heating cycle. The earth begins to heat as the sun rises in the sky by radiating heat from the ground up. This is why it is always warmest at midday. If you notice this is when the sun is at it's peak and sunlight is focused directly towards the earth. After this time it slowly start to go down and its heat isn't as direct and more at an angle to the surface of the earth. At this time it immediately begins to cool. Since just before the sun rises is the longest point in which the sun has been down it's of course the coldest time of day. It seems like at this time the temperature drops several degrees but if you were to watch a thermometer it may be just a degree or two. Our bodies are very sensitive to the change in temperature. That's what it's such a dramatic feeling if you're of watching a sun rise in the fall or winter.