Environment Canada has issued a frost warning for much of Southern Ontario including Toronto, Mississauga, Hamilton and Vaughan.

The warning says freezing temperatures are expected to start Saturday morning.

It’s the first frost warning of the season for the city of Toronto.

The cities affected by the frost warning are:

• Toronto
• London – Middlesex
• Oxford – Brant
• Hamilton
• Burlington – Oakville
• Halton Hills – Milton
• Mississauga – Brampton
• Vaughan – Richmond Hill – Markham
• Pickering – Oshawa – southern Durham region
• Stratford – Mitchell – southern Perth county
• Listowel – Milverton – northern Perth county
• Kitchener – Cambridge – Region of Waterloo
• Guelph – Erin – southern Wellington county
• Belleville – Quinte – Northumberland
• Napanee – Consecon
• Kingston – Odessa – Frontenac islands
• Brockville – Leeds and Grenville
• Ottawa
• Gatineau
• Prescott and Russell
• Cornwall – Morrisburg
• Smiths Falls – Perth – Eastern Lanark county
• Caledon
• Newmarket – Georgina – Northern York region
• Uxbridge – Beaverton – Northern Durham region
• Mount Forest – Arthur – Northern Wellington county
• Dufferin – Innisfil
• Hanover – Dundalk – Southern Grey county
• Owen Sound – Blue Mountains – Northern Grey county
• Barrie – Collingwood – Hillsdale
• Stirling – Tweed – South Frontenac
• Plevna – Sharbot Lake – Western Lanark county