1.   A thick fog formed early Monday morning, and as the temperature dropped below freezing, the fog droplets became super-cooled.

2.   In turn, water vapor in the cooling, overlying air condensed into trillions of tiny fog droplets.

3.   The chill then coaxes water vapor to condense into trillions of tiny fog droplets.

4.   The fog droplets coalesce around these substances and fall to the ground, looking a little like snow.