In our part of the country, as in others, the autumn season brings heavy morning fog. Schools here have "calamity days" built in to the schedule with the intent of using them for days when snow or ice prevents safe travel of the buses. But they find it necessary to use a few for the heavy fog that settles in at the start of the school year.
When the air reaches a temperature below the dew point, fog can form. The dew point is when the air becomes saturated while maintaining a constant barometric pressure, and it settles on the ground. Get below that, and you've got ground fog along with it. At colder temperatures, you can get hoarfrost.
Normally, this occurs in valleys and depressions. This part of northwest Ohio doesn't have valleys or depressions, so it forms a blanket of fog over the entire landscape. We use the expression "You can't see your hand in front of your face" quite a bit and sometimes it's nearly that bad. Once the sun comes up and warms the air enough, the fog dissipates.
Autumn fogs like these are as much a telltale sign of the season as the turning leaves and seeing school buses on the roads.