Thundersnow occurs when normal snowstorm clouds begin to develop upward bumps, known as turrets. These turrets are caused by instability within the storm system, combined with a strong lifting mechanism. Thundersnow is a rare winter storm event that occurs when thunder and lightning happen during a snowstorm. ... The ingredients for thundersnow are similar to a thunderstorm that forms in the summertime: warm, moist air rising toward a colder air mass above, creating instability.