Fog is essentially a cloud that forms at ground level instead of the sky.
Fog happens when the dew point and the temperature match, meaning the air is completely saturated.
Monday, the sun warmed the ground. Under a clear sky, the temperature dropped to meet the dew point, resulting in fog forming overnight. It remained dense through Tuesday morning.
Fog is one of the most hazardous weather elements to drive in, sometimes causing multi-car pile ups.
You often hear "use your low beams" when driving in fog. If you use your high beams the light bounces off water droplets and gets reflected back to you. You also want to make sure your lights are on so other cars can see you on the road.
Always slow down in fog and give yourself distance from the car in front of you.