Why is there a cold front?

Cold lake effect:

In midsummer, due to different ground conditions, the degree of air heating will vary greatly. Especially on the bare land, when the sun reaches the ground, it is easy to be reflected into the atmosphere, and the heat capacity of the ground is small, especially around noon, the exposure of the sun makes the air temperature near the ground layer very high and becomes a "heat source". On the other hand, over lakes or rivers, because there is water below, some sunlight can be transmitted, and less heat is reflected into the air. In addition, the heat capacity of water is large, which makes the temperature above the water surface relatively low. This is what we often call the "cold lake effect".

Corresponding to this is the "heat island effect".

The embodiment of the cold lake effect: on land, some places are heating up faster and the temperature is higher, which can provide water vapor and updraft continuously. When thunderstorm clouds move over rivers and lakes, due to the "cold lake effect" of the underlying surface, the air sinks, and the thunderstorm clouds will weaken or even stop immediately without the rising power and water vapor transportation.

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I hope my answer is helpful to you.