 And what happens is that if you've got cold, dense air up high in the atmosphere and it sinks and is replaced by warm, moist air, which is less dense near the surface, then that's a release of potential energy. You've got basically an object falling, and as it falls, it releases its energy and helps power the storm. And that's the energy source that blizzards use to get going and the normal sort of low-pressure systems that march every few days across the mid-latitudes.