What are the signs of the first frost thunder?

It means that there must have been convective movement of cold and warm air at that time.

Meteorologists said that although the first frost or thunder in winter is rare, it is not surprising. Thunder usually occurs in three situations: first, the ground is heated by solar radiation, which "bakes up" the air near the ground, making the density of the heated air smaller and lighter, and the heat begins to rise; Second, when the warm and humid airflow is moving, it meets the obstacles of mountains to form dynamic uplift; Thirdly, in a certain layer of the sky, there is a warm and humid airflow moving from the south, which is blocked by cold air in the opposite direction, making the warm air rise sharply and the cold air insert sharply. The first two cases can be basically ruled out when the first frost thunders. The thunder of the first frost is only the result of the collision of cold and warm air under certain conditions.