A Fog Advisory is issued by Environment and Climate Change Canada (ECCC) when widespread fog is expected to significantly reduce visibility and create hazardous travel conditions.
Fog consists of tiny water droplets suspended near the ground. When it becomes dense, visibility can deteriorate quickly and make it difficult to see roads, vehicles and other hazards.
When Is a Fog Advisory Issued in Canada?
A Fog Advisory may be issued when widespread fog is expected to reduce visibility to near zero or significantly affect travel.
Meteorologists monitor temperature, humidity, wind, cloud cover and the difference between the air temperature and dew point to determine when fog is likely to form. Local terrain and nearby bodies of water can also influence where fog develops and how long it lasts.
Fog can be difficult to forecast precisely because its formation and density can vary considerably over short distances.
Read More: How Do Meteorologists Predict Fog?
What to Expect During a Fog Advisory
Expect areas of significantly reduced visibility. Dense fog can make nearby vehicles, road signs, intersections and other objects difficult to see until you are relatively close to them.
Conditions may vary along your route. Visibility can be relatively good in one area and become severely reduced after entering a patch of dense fog.
Fog may also persist for several hours before improving as temperatures rise, winds increase or other atmospheric conditions change.
How Fog Can Affect Travel and Visibility
Reduced visibility is the main concern during a Fog Advisory.
Drivers have less time to see and react to vehicles, pedestrians, intersections and other hazards. Dense fog can be particularly dangerous at highway speeds because objects ahead may not become visible until they are much closer than usual.
Fog can also affect aviation and marine travel by reducing visibility around airports, waterways and coastlines.
What to Do When a Fog Advisory Is Issued
If you need to drive, reduce your speed and leave more distance between your vehicle and the one ahead. Be prepared for visibility to change quickly.
Use your vehicle’s low-beam headlights in dense fog. High beams can reflect off water droplets in the fog and make it more difficult to see.
Check the latest forecast and travel conditions before leaving, particularly if dense fog is expected along your route.
Related Weather Alerts
Learn More
- Fog
- Visibility
Frequently Asked Questions
Yes. Dense fog can significantly reduce visibility and make driving hazardous, particularly at higher speeds.
Visibility can become severely reduced and may approach zero in particularly dense areas. Conditions can also vary considerably over short distances.
Yes, but you should be prepared for poor visibility. Reduce your speed, increase following distance and use low-beam headlights when driving through dense fog.
No. High beams can reflect off water droplets in the fog and create glare, making visibility worse. Low-beam headlights are generally more effective.
Fog may last from a short period to several hours or longer. How quickly it clears depends on changes in temperature, wind, sunlight and other atmospheric conditions.
