Frost Risk Hits Toronto and Hamilton

By Tahani Elghazaly
Published May 11, 2026

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Parts of southern Ontario are facing an unusually cold night, with an official frost advisory in effect for Hamilton and a frost risk in Toronto from Monday night, May 11, into early Tuesday, May 12, 2026.

Environment and Climate Change Canada issued a yellow frost advisory for Hamilton at 10:40 a.m. EDT Monday, warning that patchy frost is expected overnight and into early Tuesday morning. The agency said frost may damage crops, plants and trees in frost-prone areas, and advised residents to cover vulnerable plants.

Toronto is not under an active official weather alert as of Environment Canada’s Monday afternoon update, but the city’s forecast still calls for a low of 2 C with a risk of frost overnight. That means gardens, balcony planters and sensitive spring plants could still be affected, especially in exposed or low-lying areas.

Hamilton’s forecast shows an overnight low near 1 C with patchy frost, followed by a mainly sunny Tuesday with a high of 13 C. Rain and a possible thunderstorm are expected later Tuesday night into Wednesday.

Residents are advised to cover sensitive plants, bring small pots indoors where possible, avoid late-night watering, and continue checking official weather updates, as alerts can change quickly.