Why does heavy fog sometimes appear suddenly at night?

The duration of heavy fog at night is 8-10 hours.

1. Formation

1. It is formed by radiative cooling. Most of them occur at night and early morning when it is clear and gentle, when water vapor near the ground is relatively abundant and stable, or there is a temperature inversion. Meteorologically it is called radiation fog.

2. The warm and moist air moves horizontally through the cold ground or water surface, and the water vapor in the air gradually becomes cold and liquefies to form fog. Meteorologically, it is called advection fog.

3. Smog in cities is caused by another reason, that is human activities.

2. Dissipation

1. Due to the warming of the underlying surface, the mist droplets evaporate.

2. The wind speed increases, blowing away or lifting the fog into clouds; then there is turbulent mixing, water vapor is transferred upward, heat is transferred downward, and the fog droplets near the ground evaporate.

Extended information:

The impact of foggy days:

In foggy days in urban agglomeration areas, the combination of pollutants and water vapor in the air will become It is not easy to spread, which causes most pollutants to gather at heights where people frequently move, causing certain damage to human health. Try not to engage in outdoor activities and open-air gatherings on foggy days; try to wear a mask when you must go out; do not open windows when there is morning fog.

Fog will reduce visibility and have a greater impact on highways, shipping, and maritime traffic. Zero weather often leads to highway closures and airport flight delays in many places.

Try not to drive out on foggy days. You must turn on the front and rear fog lights when driving, control the speed, and remove the fog on the windshield in time. When parking in the fog, pay close attention to the roadside and turn on the fog lights to protect people. Don't sit in the car.