Why "snow hits mountains and frost hits depressions"?

Why did the snow hit the mountain? We know that in rainy and snowy weather, whether it snows or rains depends on whether the atmospheric temperature is above or below zero degrees Celsius. The temperature on the ground and in the sky is below zero degrees Celsius, and it is snowing. Above zero degrees Celsius, it is raining. Because the temperature on the mountain is much lower than that on the flat, there is always more snow on the top of the mountain than on the flat.

The reason why there is a phenomenon of "frost cavity" is that at night, the air layer near the ground cools down first because of the continuous loss of heat on the uneven and potholed slope. Because of the high density of cold air, it flows along the slope to the bottom of the basin, just like rain falling from the sky always flows down the slope. Therefore, a large amount of cold air is always accumulated in the concave basin at night, and the temperature of the depression is lower than that of the sloping land and the flat land. This is the truth of "frost hits the hollow".