Why did the ancients say that there would be good omen after heavy snow?

Soil moisture conservation and water storage field.

It's cold in winter, and the snow often doesn't melt easily. The snow covered on the soil is very soft, and there is a lot hidden inside.

Snow means that the air is stagnant in a good year, and the air does not transfer heat, just like covering a quilt for crops. No matter how cold it is outside, the temperature below will not drop very low. Covered with winter snow, it is not easy to attract pests. After the cold wave, the weather gradually warmed up and the snow gradually melted. This not only protects crops from freezing damage, but also keeps the water melted by snow in the soil, saving a lot of water for crops, which is very beneficial to spring ploughing and sowing and the growth and development of crops.

Snow is like a wonderful carpet, covering the earth, so that the temperature of the ground will not drop too low because of the cold in winter. This heat preservation effect of snow is inseparable from its own characteristics.

As we all know, it is warm to wear a cotton-padded jacket in winter. Why is it warm to wear a cotton-padded jacket? This is because the porosity of cotton is very high, and the pores of cotton are filled with a lot of air, which has poor thermal conductivity. This layer of air prevents the heat of human body from spreading outward. The snow covering the breast of the earth is like cotton, and the porosity between snowflakes is very high. It is this layer of air that drills into the pores of the snow to protect the ground temperature from falling very low. Of course, the thermal insulation function of snow changes with the density at any time. This is like wearing a new cotton-padded jacket, which is particularly warm, and the old cotton-padded jacket is not very warm. The density of fresh snow is low, and there is a lot of air stored in it, so the heat preservation effect is particularly strong. Chen Xue is like an old cotton-padded jacket, with high density and weak heat preservation effect, because there is less air stored in it.

This is because air is a bad conductor. As we know, any object itself can transfer heat, and this property of transferring heat is called the thermal conductivity of the object. Among several common substances in nature, air has the worst thermal conductivity. Therefore, the more air an object contains, the worse its thermal conductivity. Because the amount of air contained in snow changes greatly, the thermal conductivity of snow also changes greatly. Generally, the newly fallen snow has large pores and the best heat preservation effect. In the late stage of snow melting in spring, snow is soaked by water, and its thermal conductivity is closer to that of water, so the thermal insulation effect of snow tends to disappear.

Snow contains a lot of nitrides. It is observed that if 1 liter of rain can contain 1.5 mg of nitride, then 1 liter of snow can contain 7.5 mg of nitride. When the snow melts, these nitrides are brought to the soil by snowmelt water and become the best fertilizer.

Snow has a thermal insulation effect on the soil, which is temporarily beneficial to pests who go underground for the winter. But when snow melts, it absorbs a lot of heat from the soil. At this time, the soil will suddenly become very cold, the temperature will drop a lot, and pests will freeze to death.

Therefore, several heavy snows in winter are a harbinger of a bumper harvest in the coming year.