Rain is forecast to start tonight and continue throughout tomorrow.
The rain will turn to snow by tomorrow evening, following the passage of a strong cold front.
Environment Canada says several centimetres of snowfall will be possible by Friday morning, but it's uncertain how much snowfall each area of the region will get.
They do warn that hazardous driving conditions may occur, and they advise motorists to drive with caution.
You can report severe weather by sending an email to ONstorm@canada.ca or tweet reports using #ONStorm.
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