On snowy days, there was thunder and thunder

In the early hours of this morning in Shanxi, when the blizzard that was flying in the sky had been falling madly, the thunder was actually shaking, and the people who heard the thunder could not believe that the winter of the snowy day could still hear the thunder and shake the sky, which was really unbelievable. The 90-year-old grandmother next door said she had lived so long and had never seen such a situation. What does this kind of day indicate...