Why is it so foggy at night?

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asked May 10 in Weather by cozycoupe (1,680 points)
Why is it so foggy at night?

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answered May 11 by NattKeuggton (5,550 points)
The reason it's so foggy at night is because of radiation fog which forms at night under clear skies with calm winds when heat is absorbed by the earth's surface during the day is radiated into space.

As the surface of the earth continues to cool,provided a deep enough layer of moist air is present near the ground and the humidity will reach 100 percent and fog will form.

Fog is worse at night and as the night progresses.

As long as there is sufficient moisture in the air, fog will begin to form as the night progresses.

The most common way for fog to form is is through steam fog which forms when cold air moves over warm water.

When cool air mixes with the warm moist air over the water, the moist air cools until it's humidity reaches 100 percent and as a result fog forms.

The time of day that fog is most common is in the morning just before sunrise or it can also occur during sunrise or at sunset.

Fog most often occurs in the morning because the morning is the coolest time of day when the temperature drops to the dew point temperatures and the relative humidity approaches 100 percent.

Most fog will completely go away and dissipate within a few hours after sunrise.

The difference between fog and mist is how far you can see through them.

Fog is when you can see less than 1,000 meters or 0.62 meters away and if you can see further than 1,000 meters or 0.62 miles away then it's mist.

Fog is also when microscopic droplets reduce the horizontal visibility at the Earth's surface to less than 0.62 miles and mist is when droplets do not reduce the horizontal visibility to less than 0.62 miles.

Mist is considered synonymous with light fog.

The temperature at which fog forms is any air temperature and dew point that is less than 4.5 F.

The fog begins to form when the water vapor condenses into tiny water droplets which are suspended in the air.

The main cause of fog is water vapor or water in it's gaseous form condensing.

During condensation, the molecules of water vapor combine to make tiny liquid water droplets which hang in the air.

And because of the tiny water droplets you can see the fog.

The water vapor itself is a gas that is invisible.

And steam fog forms when cold air moves over warm water.

When the cool air mixes with the warm moist air over the water, the moist air cools until its humidity reaches 100% and fog forms.

Warm air, air blows in from the south and if there is snow or cool moisture on the ground it will come in contact with the warm, moist winds.

This contact between the air and ground will cause the air blowing in to become cool.

Then dew point rises and creates high humidity and forms fog.

Fog normally occurs at a relative humidity near 100%.

This occurs from either added moisture in the air, or falling ambient air temperature. However, fog can form at lower humidity, and can sometimes fail to form with relative humidity at 100%.

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