How does a snowstorm happen?
Snowstorms can be on different scales. You can have Alberta clippers, Panhandle hooks, or Nor'Easters that affect entire regions. In addition, you can have lake effect snow squalls that affect a mesoscale area of only a few square miles. Larger scale snowstorms usually involve low pressure centers and moisture from an ocean. Lake Effect requires moist, unsettled, cold air flowing over relatively warm lake/sea water.