Provincial police say all roadways in Dufferin County north of Toronto are now open.
Police say the snowfall combined with high winds has produced hazardous conditions.
Blowing snow has cut visibility to nil in many areas.
Major routes have been cleared, but drifting caused by blowing snow has made back roads impassable until they are plowed.
Environment Canada says the strong weather system that has been hovering over eastern Ontario will track north to southern James Bay by this evening, bringing significant snowfall and strong winds to parts of northeastern Ontario.