Travel Weather
Dense Fog Advisory Explained: Visibility, Driving, and Freezing Fog
What a dense fog advisory means, why fog can form quickly, and how to drive more safely when visibility drops.
Quick answer: A dense fog advisory means visibility is expected to be greatly reduced, often making driving more dangerous.
How fog forms
Fog forms when air near the ground becomes saturated. Clear nights, light wind, moist ground, snow cover, or nearby water can all help.
Fog can be patchy, which makes it especially dangerous on roads.
Driving risk
Slow down, use low beams, leave extra space, and avoid sudden stops. High beams can reflect back and make visibility worse.
Visibility can drop rapidly near valleys, rivers, bridges, and low spots.
Freezing fog
When fog droplets freeze on contact, roads, sidewalks, and elevated surfaces can become slick.
Treat freezing fog as both a visibility hazard and an icing hazard.