After the dark clouds pass in summer, why does it rain more heavily on a very white day?

Most of the rain in summer is frontal rain (the heavy rain in the afternoon in summer is convective rain). The temperature in summer is high, so the air is heated and rises. At this time, if a burst of cold air blows, then at the interface of hot and cold air (Imagine that this is a curved surface, which can be obtained by translation of half a parabola, or you can imagine the shape of a wave). When the water vapor is cooled, it liquefies and condenses into small water droplets. These water droplets can scatter or emit light, making the sky look darker. , when the junction happens to pass by, the sky is darkest because the water droplets are scattered or refracted the most, but because the water droplets are still in the process of condensation, there are not many water droplets falling, and the cover junction passes quickly, so it is dark The time is not too long. After the interface passes, the sky will become brighter. Since there are clouds at high altitude, the light entering the space will be scattered multiple times in the space between the clouds and the ground, making the sky look brighter. The front The rain formed at the junction and the rain formed aloft will fall behind the front, so the rain after dawn will be heavier than when it is dark. Frontal rain mostly rains on the cold front, and it falls after the cold front has passed, so it is post-frontal rain. This is why the day after it rains in summer becomes colder.