what is freezing fog why is it dangerous
Freezing fog is a type of fog that forms when temperatures are at or below freezing, but the tiny droplets in the fog are still liquid (supercooled) and then freeze on contact with surfaces.
What is freezing fog?
- Fog is essentially a low cloud made of tiny liquid water droplets near the ground.
- In freezing fog, air temperature is at or below 0°C (32°F), yet the droplets remain liquid until they hit a surface such as roads, trees, cars, or power lines.
- When they touch these cold surfaces, they freeze immediately, forming a coating of ice or feathery rime ice.
A simple way to picture it: imagine regular fog that quietly paints everything it touches with clear or white ice.
Why is freezing fog dangerous?
Freezing fog is dangerous because it combines very low visibility with hidden ice.
1. Sudden, invisible ice on roads
- Moisture from the fog deposits on cold roads, bridges, and overpasses and then freezes, creating icy patches and black ice.
- Drivers may not realize the road is icy until they brake or turn, which can cause skids and accidents, especially during the morning commute.
2. Very poor visibility
- Like regular fog, freezing fog often reduces visibility to less than 1,000 m (and sometimes a few hundred meters or less), which makes it hard to see other vehicles, pedestrians, or hazards.
- When visibility is low and grip is reduced at the same time, small mistakes (like speeding slightly or braking late) become much more dangerous.
3. Ice build‑up on surfaces and infrastructure
- The supercooled droplets freeze on contact and form rime ice on trees, railings, towers, and power lines.
- Heavy rime can add weight, sometimes leading to branches snapping or strain on power cables and masts, which can contribute to power cuts or minor structural damage.
4. Risks to aircraft and transport
- In aviation, freezing fog is specifically noted (code FZFG) because it deposits ice on aircraft surfaces during taxi, takeoff, and landing.
- Even thin frost or rime must be removed before flight, and anti‑icing is needed to prevent further build‑up, as ice can affect lift and control.
When and where does it usually happen?
- Freezing fog tends to form on clear, calm nights or early mornings when the ground rapidly cools, especially in winter.
- It is more common in valleys, low‑lying areas, and spots where cold air settles and moisture is abundant (near rivers, lakes, or after snowmelt).
Quick safety tips in freezing fog
- Slow down well below the speed limit and increase following distance; avoid sudden braking or sharp steering.
- Use low‑beam headlights or fog lights, never high beams (they reflect off fog and reduce what you see).
- Be extra cautious on bridges, overpasses, and untreated side roads, where ice forms first.
- Clear ice from windows, mirrors, and lights before driving, and watch for ice build‑up on steps and walkways around your home.
In short, freezing fog is dangerous not just because you can’t see well, but because it quietly turns surfaces—especially roads—into ice without looking obviously snowy or frozen.
Information gathered from public forums or data available on the internet and portrayed here.