I would guess this is about the first time it has gotten into the 40's overnight since the new roof. As the other guys said, moisture will condense on a roof overnight, either as droplets or as frost, then evaporate in the morning as the air heats or the sun hits it - presto, instant miniature fog bank. Most noticeable when looking right along the plane of the roof, and more so usually on humid, misty mornings or on cold frosty mornings when the sun first hits the roof, when the moisture does not evaporate into the surrounding air immediately, but forms a fog before it dissipates. By 9:00 the surrounding air had heated enough that the surrounding air humidity dropped off from the near 100% it got to when the night air cooled, so it could then immediately absorb the moisture and was no longer forming a visible fog trail.
If coming from A/C vent (which would almost certainly be the furnace, not A/C vent, maybe you caught it right after the furnace shut off, so humid inside air was coming out of the vent into colder outside air - again, instant fog. Same thing you see coming from the furnace exhaust (assuming you have gas or oil furnace) on cold days, the moisture in the exhaust gas will condense into a slight fog that you will see drifting away from the exhaust cap - that is water vapor you are seeing, not smoke, as gas furnaces almost never smoke (unless TERRIBLY starved for air), and oil furnaces rarely put out visible smoke except occasionally for the firt second or two after firing up. Also - smoke would almost always be gray or black - water is white.
If there is no smell in the attic, as you say, and no funny smell around the A/c or furnace, then I would not be concerned. If it really nags at you, then you (or someone) would have to get up on a ladder and sniff at it to see if it smells like smoke or not, but not likely.