Nearly every summer rainstorm comes with thunder and lightning. Yet during even the blusteriest blizzard, there's nary a spark in the air. It can occur (although snow lightning strikes just six times a year on average in the U.S.), but winter air doesn't make for prime lightning-forming conditions, says meteorologist Robin Tanamachi of the University of Oklahoma.
During the summer, the lower atmosphere is full of warm, humid air. Above that, it's cold and full of ice crystals. As the warm air rises, it carries water vapor with it, these molecules brush against the ice crystals, and this friction creates an electric field in the cloud -- like scuffing your feet across a carpet. The ice crystals gain a slight positive charge, and the updraft carries them to the top of the cloud, giving the cloud's bottom a net negative charge. Once the difference between the negatively charged cloud bottom and the positively charged ground becomes great enough, a bolt arcs between them.
But in snowy months, the atmosphere is cold and dry throughout, so there's no updraft to create friction within the clouds. Wind stirs the molecules and crystals some, but that action rarely generates a strong enough electric field to spark lightning.
I have seen lightning in a snow storm. I guess that I was pretty lucky to see that one out of six chances to see lightning in a snow storm. I have been studying Meteorology for eight years now so this artical is truly remarkable.
Thundersnow (as we call it) is not uncommon in NW PA.
Lightning and thunder are actually fairly common in winter storms. Just watch The Weather Channel where there has been at least three or four cases this winter where meteorologists out in the field have recorded lightning and thunder while doing their reporting on-air. In fact, on the Great Lakes, smaller scale early season lake-effect snow storms containing lightning and thunder on Lake Erie and Ontario are quite common. Some of the more intense larger scale winter storms each season are also accompanied by lightning and thunder from St. Louis to Washington DC to Boston. If you do a literature search you will find lots of research papers regarding this winter time phenomenon.