Dense fog advisory
A Dense Fog Advisory is issued by the National Weather Service when widespread fog lowers visibility to 1/4 mile or less, making travel difficult. It is the highest fog alert the NWS issues; there is no separate dense fog warning.
Right now2Dense fog advisories in effectas of Every term in the storm glossary
Dense fog vs freezing fog
| Advisory | Visibility | Temperature | Main danger |
|---|---|---|---|
| Dense Fog Advisory | 1/4 mile or less | Can be above or below freezing | Difficulty seeing while driving |
| Freezing Fog Advisory | About 1 mile or less | At or below freezing | Ice forming on roads, bridges, and windshields |
Where fog comes from
- Radiation fog forms on clear, calm nights when the ground cools quickly and moist air near the surface condenses. It usually burns off by mid-morning.
- Advection fog happens when warm, moist air moves over a colder land or water surface. It can stick around all day.
- Valley fog collects in low-lying areas when cooler air sinks and moisture gets trapped in the valley.
- Sea fog develops when warm air passes over cooler ocean water, common along coastlines.
Driving in a dense fog advisory
- Slow down and give yourself extra time to react.
- Use low beams instead of high beams, because high beams reflect off the fog and make it harder to see.
- Guide yourself with the right edge line of the road rather than the center line.
- Leave extra following distance between your car and the one ahead.
- Avoid using cruise control. If visibility gets too poor, pull fully off the road, turn off your lights, and set the parking brake so other drivers do not follow you.