Hydro One, the provincial utility, has reported that the number of customers without power soared to more than 60,000 as of Sunday morning.
After hammering areas further north, snow squalls off Lake Huron and Georgian Bay were forecasted to move into southwestern Ontario.
Environment Canada has warned that areas around London, the Bruce Peninsula and Collingwood could be in store for more than 30 centimetres of snow by Tuesday.
A winter weather travel advisory was also in place for a band stretching from around Kitchener to Newmarket, where the forecast suggested between five and 10 centimetres of snow could fall Sunday.
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