How is thunder formed?

Lightning is a discharge phenomenon in thunderstorm clouds.

Thunderstorm clouds generally have two conditions, sufficient water vapor and strong convection. In winter, because the air is cold and dry, the solar radiation is weak, and convection is not easy to form in the air, so lightning is rare. But sometimes when the temperature is high in winter, it will form thunderstorm clouds, leading to lightning and rain and snow. Convection is particularly strong, and it can also form hail, which will produce the weather phenomenon of "thunder in winter". Knowing these reasons, it is not surprising that it thunders in winter.