Some areas at risk of frost around Toronto include: Alliston, Barrie, Bracebridge, Caledon, Cambridge, Collingwood, Gravenhurst, Guelph, Haliburton, Kawartha Lakes,Kitchener-Waterloo, Muskoka, Newmarket, Orangeville, Orillia, Peterborough, Port Perry and more.
The frost risk is due to a cool ridge of high pressure that will drift across southern Ontario tonight. However Toronto proper will mostly avoid the cold temperatures.
Environment Canada urges those in affected areas to cover plants and frost-sensitive trees.
Weather watchers had previously predicted a longer summer after last winter's brutal Polar Vortex winter. But the first day of Autumn is not until Tuesday, meaning many Ontarians will face frost during the summer season.