Ascent so often in the cool season is sloped ascent too. So the rising air at 850 mb doesn't go straight up, it slopes towards the colder air (i.e. north) and continues rising through 700 mb.
That's a signal for widespread, broadbrushed snow. When you start stacking 700 mb lifts on top of 850 mb lift, that's when you get concentrated bands of heavy snow.