In general, why is precipitation associated with the fronts between warm and cold air masses?

Question

Can someone please provide a relatively simple answer for me? I'm very foggy on this topic even after reading about it on numerous web pages.

Answer 1

Simple. When cold air and warm air collide, the warm air is forced to rise, since it is less dense. Then, it expands due to lack of friction as it moves higher up into the atmosphere. Then, it reaches dewpoint and condenses, becoming clouds. The warm air forms clouds, and clouds mean rain. So it rains.

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Answer 2

When it comes to weather, there rarely is a simple answer.

Often, I see text books that say this and while the boundary area between two different air masses (sort of a simple definition of a front) often does cause precipitation, most rain and thunderstorms occur in areas well away from a classical frontal boundary.

That is not to say that fronts doesn't cause precipitation because they often do.

Much of the time fronts will travel through an area and cause no rain at all due to moisture limitations and the weakness of the front.

The main reason that you often find this statement is that the author is oversimplifying a very complex process so that someone without a strong background in physics (thermodynamics) and atmospheric processes can comprehend.

In other words, it is sort of like a half-truth that is often used to explain things in a reasonable fashion so most people can understand.  

As in most cases with complex science topics, there is a lot of misinformation that we are taught that when on closer examination are true only part/most of the time but not all the time.