You do realize that unless you have a S.D. waterfowl permit NOW. You may not get one! They are limited or short duration in the Dakota's. I doubt any weather so far will impact the population up there. Many stay till after freeze up, you need to consentrate on moving deep water later on, that's mostly the Missouri river, requires hard core watefowling boats and gear, when it gets mild, they will go back to unfroze marshes for how long it lasts, ice and snow shutting of the food source is what makes them move out, but they only go so far. What ever snow and weather will not stay permanantly till a little later normally, but it might be a long and harsh winter, from what's out there now. If your contemplating going I would talk to the S.D. fish and game, about licenses since they can be a lottery, like a big game license.