Question #0ebf7

1 Answer
Aug 9, 2016

Usually fog forms.

Explanation:

I did not see this question until now. Hopefully the answer is still of use to you.

There are really only 2 variables in the atmosphere and everything else is a result of them, and those are heat and moisture content. In the question that you have posted, there is no mention of water content, so we have to strictly look at the temperature. In the case when a warmer air mass moves over a colder air mass the first thing that is going to happen is the air is going to loose heat to the ground. There are a few different processes that can be at work (radiative cooling, conduction and turbulent mixing), but the end result is the air loses heat to the ground.

Air can only hold so much water vapor (humidity) dependent on the temperature of the air. The ratio of the actually humidity to the maximum amount of humidity the air can hold is called the Relative Humidity. The following graph demonstrates.

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So what happens when the air cools is it gets closer and closer to the maximum amount of water vapor it can hold. Once it hits that temperature (called the dew point), it is at 100% relative humidity and the water vapor begins to turn back into liquid water. The drops of liquid water that form are very small (1,000,000 drops are needed to form a regular rain drop), so they stay suspended in the air. The liquid water particles are what we see when we see cloud. Cloud that forms at the surface of the Earth is called fog.

So in this case if the ground cools the air enough to reach 100% relative humidity then fog will form.