Wet and cold is the big killer. If wintersowing in containers you need to keep them out of the rain or snow (most folks put lids on them with air holes punched in them) or you can store them somewhere that stays dry. Most seeds that need cold stratification need to swing from warm to cold many times so don't worry about how cold it gets or how warm some of the days will be. Fruit trees that need 'chill hours' need a certain number of hours in a specific range of temperatures in order to bloom and fruit successfully (most will still bloom a little, just not as much). Usually the required temp is in the thirties and forties, so if we get really cold it does not help them meet their chill hour requirement.

Thanks John,