Will There Be Fog Tomorrow?

Quick answer: it is fog when visibility falls below 1 km (about 0.6 mile) and dense fog below 200 m; in the US a dense fog advisory starts at a quarter of a mile. Fog forms most often after clear, calm nights and is thickest from late night to about 9am. Enter your town to see the forecast visibility for tonight, tomorrow morning and the next 48 hours.

Driving in Pakistan? See the motorway fog status for M-1, M-2, M-3, M-4, M-5, M-9 and N-5, updated every hour.

How it works

What the fog levels mean

Dense fog: visibility under 200 m (about 650 ft). The India Meteorological Department calls 50-200 m "dense" and under 50 m "very dense" fog.
Fog: visibility under 1 km (0.6 mi), the World Meteorological Organization definition, or the model's own fog weather code. Fog at or below 0°C is flagged as freezing fog, which can glaze roads.
Mist or haze: visibility 1-2 km, or air almost saturated with light wind, when fog can form even if the model's visibility stays higher. With dry air, low visibility is labelled haze or smog.
Clear: 2 km (1.2 mi) or more.

Times are the place's local time. Forecast: Open-Meteo hourly visibility, weather data by Open-Meteo.com (CC BY 4.0), refreshed at most every 45 minutes. Place names: GeoNames (CC BY 4.0). A model forecast can miss patchy fog in valleys and over rivers; it is not a measurement on your road.

Official meaning

Fog warnings and advisories

United States: the National Weather Service issues a Dense Fog Advisory when widespread fog cuts visibility to a quarter of a mile or less, and a Freezing Fog Advisory when fog forms below freezing (visibility typically a mile or less). Find yours on US weather warnings.
United Kingdom: the Met Office issues yellow fog warnings when widespread fog is expected to disrupt travel. See UK weather warnings.
Pakistan: the Motorway Police (NHMP) close motorway sections in dense fog and post updates on nhmp.gov.pk; helpline 130. Our motorway fog status page tracks the forecast section by section.
India: the India Meteorological Department issues fog alerts by district on mausam.imd.gov.in.

Safety

How to drive in fog

Before you enter fog, check your mirrors and slow down. A "Fog" sign on a clear road means a fog bank may be just ahead (Highway Code rule 234).
Drive so you can stop within the distance you can see clearly, and leave a much bigger gap: following the tail lights in front gives a false sense of safety (rule 235).
Lights: use dipped headlights when you cannot see more than 100 m (328 ft) (rule 226). Use fog lights only when visibility is seriously reduced, and switch them off when it improves, because they dazzle and can hide your brake lights (rule 236). Do not use full beam: it reflects off the fog.
Use wipers and demisters, watch for drivers without lights, and do not speed up to escape a vehicle that is too close behind you.
At junctions, open the window, listen for traffic, and pull out only when you are sure it is safe.
If you break down, get off the road if you can, switch on hazard lights and stand well away from traffic.

Source: The Highway Code, rules 226 and 234-236 (GOV.UK, Open Government Licence v3.0), summarised. The rules are for Great Britain; the safety advice applies anywhere. This is general information, not legal advice.

Questions

Fog forecast — FAQ

Will there be fog tomorrow morning?

Enter your town above: the checker reads the hourly visibility forecast and tells you whether visibility is forecast to fall below 1 km (fog) or 200 m (dense fog) tonight and between 6 and 10am tomorrow. Fog is most likely after a clear, calm night, especially after rain, near rivers and in valleys.

What does a dense fog advisory mean?

In the United States, a local National Weather Service office issues a Dense Fog Advisory when widespread fog cuts visibility to a quarter of a mile (about 400 m) or less. A Freezing Fog Advisory means fog is forming while it is below freezing, so droplets can freeze on roads and windscreens; visibility is then typically a mile or less.

When should you use fog lights?

In the UK the Highway Code says you must use headlights when you cannot see more than 100 metres (328 feet), and you must not use front or rear fog lights unless visibility is seriously reduced, because they dazzle other drivers and can hide your brake lights. Switch them off when the fog clears. Other countries have similar rules.

What time does fog usually clear?

Radiation fog, the common kind on calm winter nights, usually thins two to four hours after sunrise as the sun warms the ground, so mid-morning. In midwinter, under cloud or in valleys it can last all day. The hourly table shows when the forecast visibility recovers.

What is the difference between fog and mist?

Both are tiny water droplets in the air. The World Meteorological Organization calls it fog when visibility is below 1 km and mist when it is 1 km or more. Haze and smog are dry particles such as smoke and dust, not droplets.

Is this forecast accurate for my road?

It is a weather model on a grid of about 2-25 km depending on the country, refreshed at most every 45 minutes. Models handle widespread fog well but can miss patchy fog in hollows, over rivers and on high ground. Always check official warnings and road-authority traffic news before you set off.