What is the weather sign of fog?

The weather sign of fog is shown in the picture.

The fog warning signal is divided into three levels, which are represented by yellow, orange and red respectively. Fog yellow warning signal, fog with visibility less than 500 meters may appear within standard 12 hours, or fog with visibility less than 500 meters and greater than or equal to 200 meters has appeared. The standard of orange warning signal for fog is that fog with visibility less than 200m may appear within 6 hours, or fog with visibility less than 200m and greater than or equal to 50m has appeared and will continue.

The red warning signal standard for heavy fog is that fog with visibility less than 50 meters may appear within 2 hours, or fog with visibility less than 50 meters has appeared and will continue. If there is foggy weather, you should drive very carefully.

When the water vapor contained in the air reaches the maximum, it reaches saturation. The higher the temperature, the more water vapor is contained in the air. If the water vapor in the air near the ground is more than the saturated water vapor at a certain temperature, the excess water vapor will condense out. When enough water molecules combine with tiny dust particles in the air, the water molecules themselves combine with each other and become small water droplets or ice crystals, which is fog.

The water vapor in the air exceeds saturation and condenses into water droplets, which is mainly caused by the drop in temperature, which is also the reason for the foggy morning in autumn and winter. Fog and clouds are caused by the drop of temperature, and fog can actually be said to be a cloud near the ground.