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Fog Hazards

Table of Contents

Introduction

Fog is one of the most underestimated weather hazards, yet it causes hundreds of crashes, pile-ups, and delays every year. Visibility can drop from clear skies to near zero in just minutes, leaving drivers, pilots, and pedestrians dangerously unprepared.

Beyond the roadways, fog disrupts aviation, shipping, rail traffic, and even routine daily activities like children walking to school. Freezing fog compounds the threat by coating roads and walkways with ice.

This guide outlines the main types of fog, the risks they create, and the protective steps you can take. Recommendations are based on guidance from the National Weather Service, the UK Met Office, aviation authorities, and emergency management organizations.

Hazard Types

Dense Fog
When visibility falls below 200 meters (especially under 50 m), conditions become extremely dangerous. Dense fog causes traffic accidents, transport delays, and widespread disruption.
Freezing Fog
Forms at or below freezing temperatures. Water droplets freeze on contact, leaving a dangerous glaze of ice on roads, sidewalks, vehicles, and power lines.
Radiation Fog
Common in valleys and low-lying areas. Develops overnight when air cools under clear skies and calm winds, often persisting through the morning commute.
Advection Fog
Occurs when warm, moist air flows over a colder surface. Frequently affects coastal regions and can spread inland with onshore winds.
Upslope Fog
Created when moist air is forced up terrain slopes or mountainsides, cooling and condensing into fog.
Frontal / Precipitation Fog
Forms along weather fronts when rain evaporates into cooler air, lowering visibility.
Impact Areas
Roads, airports, harbors, railways, and pedestrian routes are all vulnerable, with accidents and delays possible across multiple sectors simultaneously.

Preparation

Before the event

  • Monitor official forecasts for Fog Advisories or Dense Fog Warnings.

  • Plan alternate travel routes that avoid valley bottoms, bridges, and exposed highways.

  • Inspect your vehicle: ensure all headlights, taillights, and fog lights work properly. Clean windshields and mirrors.

  • Carry spare bulbs and emergency supplies in your vehicle.

  • For aviation and marine operators: review METAR/TAF or port visibility forecasts before departure.

  • If household members are prone to anxiety or disorientation, prepare coping strategies such as slowing down, waiting it out, or avoiding risky crossings.

Checklist essentials

Reliable weather alert systems (NWS, Met Office, local warnings).
Flashlight and reflective vest in the car.
Fully charged phone for emergencies.
Long-distance travel kit: warm clothing, water, emergency triangle, backup GPS.
Aviation/marine: visibility, altimeter, and radio equipment checked and ready.

During the event

  • Slow down—reduce speed and increase following distance.

  • Use low-beam headlights. Never use high beams; they reflect and worsen glare.

  • When visibility drops below 50 meters, use fog lights (if available) and hazard lights.

  • Never stop in moving lanes of a roadway. If necessary, pull well off the road and turn off all lights to avoid being struck from behind.

  • Avoid overtaking, lane changes, and distractions such as phones or radio.

  • Aviation and maritime operations: delay departures, follow standard visibility protocols.

  • Pedestrians: wear bright or reflective clothing, avoid crossing busy roads during heavy fog.

After the event

  • Wait until fog has fully lifted before resuming normal travel speeds.

  • Check surfaces for ice if freezing fog was present.

  • If flights or ships were delayed, follow official instructions until conditions improve.

  • Inspect your vehicle for condensation on lights and mirrors.

  • If fog caused disorientation or anxiety, take time to rest and reorient before resuming activities.

Special Populations

Children

Supervise children closely at bus stops or walking to school. Equip them with reflective clothing or backpacks.

Older Adults

Seniors may be more vulnerable to disorientation or falls, especially during freezing fog. Delay travel when fog is dense.

People with Disabilities / Medical Needs

Visual or hearing impairments can make fog more dangerous. Arrange transportation in advance when low-visibility events are forecast.

Businesses

Delay non-essential deliveries and transportation. Provide drivers with alternate routes and training for fog response.

Pets

Avoid walking pets near traffic. Use reflective collars, leashes, and short leads to maintain control.

Quick Reference Tables

Fog Alert Guidance
Alert Level Visibility Action
Advisory / Watch < 1,000 m Monitor forecasts, prepare for slower travel
Dense Fog Advisory < 200 m Delay travel if possible
Hazard / Emergency < 50 m or near zero Stop safely, avoid driving, wait for clearing

Freezing Fog Note: Treat all exposed surfaces as icy. Drive and walk with extreme caution.

Additional notes/thoughts

Before your next journey, ask:

  • Am I traveling through a fog-prone area, especially at night or early morning?

  • Is my vehicle prepared with working fog lights and clean glass surfaces?

  • Does my family know the rules for driving or walking safely in low visibility?

  • For aviation or marine operations: am I monitoring current forecasts and legal requirements?

Fog can appear suddenly and last for hours. Preparation, awareness, and patience are essential to prevent accidents and protect lives.

References

Image Credits

https://unsplash.com/photos/a-foggy-street-at-night-with-street-lights-3C6DIGvZfEw

https://unsplash.com/photos/gray-asphalt-road-during-sunset-hK6tBRanE-Q

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