The idea is that animals can sense weather changes; therefore, if they feel a serious bout of weather (storms, snow, etc) coming on, they'll get out and feed so they won't go hungry while the storm's on. And it holds fairly well true, I'd say. If you see a blizzard or a tropical storm in the forecast, hunting the 12-24 hours before it wouldn't be a bad idea... as long as you time it right.