Why is it so cold in the northeast?

As the saying goes, an autumn rain brings a cold. The temperature in the northeast is from August to September in the lunar calendar, and it gets cold when it gets cold. A cold air came, which was green yesterday and turned yellow today. I remember when I was a child, it snowed at 65438+ 10/month. The cold weather in the three northeastern provinces is mainly affected by the cold air from Siberia.