I remember the weather man on TV explained why this happens, but I can't remember what the explanation was.

It seems that the temperature drops just after sunrise for a while before warming up again ... summer or winter.

Does anyone know why this happens?

I do a lot of night work, and can tell you that in Australia, at least, it gets colder between 3:30 and 4am, well before sunrise.

It usually stays that way till about an hour after sun-up, whatever season it is.

I believe is is a function of sundown rather than sunrise- it is the natural cooling effect of a few hours of darkness.

On a bit of an aside, whoever said that the 'darkest hour is just before dawn' is a long way off the mark- it is usually darkest between midnight and 4am...

The earth's atmosphere is heated, not directly by the sun's rays, but by heat radiation given off from the surface. The earth's surface keeps radiating heat even after sunset, but by 3:00 AM, it has cooled down, and hence that's when the earth's surface is at its coolest. Once the sun rises, obviously the temperature starts rising again.

Morning dew neads about half to three quarters of an hour to evaporate fully . remember evaporation=cooling.