What is the principle of snowfall caused by the Great Lakes effect?

The principle of snowfall caused by the Great Lakes effect is similar to that of warm front. Warm front refers to the front that warm air pushes the front to move to one side of the cold air mass during the front movement. The warm front moves slower than the cold front, which may cause continuous precipitation or fog.

It is precisely because the temperature of cold air passing through the lake has increased that when it moves to the lake shore, the temperature of air from the lake shore is higher than that from the land on the lake shore. The air from the lake is equivalent to a warm air mass, and the land on the shore of the lake is equivalent to a cold air mass. The warm air mass actively moves to the cold air mass, which is a warm front and forms snowfall.

After the warm front crossed the border, the warm air mass occupied the position of the original cold air mass. Warm fronts are mostly active in northeast China and the middle and lower reaches of the Yangtze River, and are often accompanied by cold fronts. When the warm front crosses the border, it is warm and humid, the temperature rises, the pressure drops, and the weather turns cloudy and rainy.

In the warm front, the warm air mass slides slowly upward along the front in the process of pushing the cold air mass, and is adiabatic cooled during the sliding process. When it reaches the condensation height, a cloud system is produced on the front. If the sliding height of warm air is high enough and the water vapor is sufficient, a broad and systematic layered cloud system will often appear on the front.

Typical cloud sequences are cirrus, cirrostratus, stratosphere and nimbostratus. The thickness of the cloud varies with the rising height of warm air, which can generally reach several kilometers. The thicker it is, the thicker it can reach the tropopause. The closer it is to the ground front, the thicker the cloud is. Warm front precipitation mainly occurs in the rain layer, mostly continuous precipitation.

The width of precipitation varies with the slope of the front, generally 300-400 kilometers. Because of the uneven distribution of air humidity and vertical velocity, the warm front cloud system is sometimes discontinuous, and there may be a cloudless gap of several kilometers or even hundreds of kilometers.