Frost risk overnight as temperatures drop to 3°C, first day of autumn arrives Tuesday
Environment Canada is asking Ottawa residents to bring in cold-sensitive plants and crops as patchy frost becomes likely overnight Monday into Tuesday, the first day of autumn.
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Frost is likely overnight Monday into Tuesday, September 22 — the first official day of autumn — as temperatures in Ottawa drop to around 3°C, Environment Canada says.
Conditions are favourable for frost development overnight Monday, with patchy frost expected Tuesday morning. The Monday afternoon high peaked at 16°C, but the overnight low will fall dramatically. Tuesday's high is expected to reach 17°C before dropping again in the evening.
Environment Canada is asking residents to move cold-sensitive plants, trees and crops indoors if possible, as frost can cause damage. No rain is forecast for the coming week, with clear, sunny days and cool overnight lows expected through the period.
The dramatic temperature swing marks a sharp seasonal transition as the region enters autumn.
The facts
When is the first day of autumn in 2026?
Tuesday, September 22, 2026.
How low will temperatures drop overnight Monday into Tuesday?
Temperatures in Ottawa will drop to around 3°C overnight Monday into Tuesday, September 22.
What is Environment Canada asking Ottawa residents to do?
Environment Canada is asking residents to move cold-sensitive plants, trees, and crops indoors if possible, as frost can cause damage.
