Thundersnow is when precipitation is falling so quickly that it is actually a thunderstorm, with lightning and thunder. But the temperature is below freezing in the atmosphere, so the precip. falls as snow. The lightning is still dangerous. I’ve seen it happen once, during the 1993 “blizzard” in GA.
This video takes a few minutes to get to the thundersnow explanation, but it does. Thank you WSB.TV Atlanta.