system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5:Why are snow storms with lightning so rare? What prevents them from occurring?
gpt
Thunderstorms require a lot of warm, moist air moving up while a lot of cold, dry air is moving down. The warm air gets high enough that water droplets condense and make big clouds. The more air moving around, the bigger the cloud. The lightning comes from a build up of static electricity from the different air currents moving against each other. 

If it's snowing, chances are there isn't enough warm air to form the right conditions. Snow requires cold, moist air. Dry air is much better at forming static electricity, and there generally aren't masses of air moving against each other when all the air is cold, like there would be if some was warm and some was cold. 

Hail can often coincide with thunderstorms, however, because it's formed differently. When all that air is moving upwards, it can create some extremely powerful updrafts. Sometimes they're strong enough to push water high enough for it to freeze into hail before falling down again, even if it's much warmer down near the surface.