Heat warning in effect for Ottawa and region to kick off summer

Here is your local and regional forecast for Ottawa on June 21, 2025.

A heat warning has been issued for eastern Ontario and western Quebec by Environment Canada.

The weather agency issued the warning Saturday morning, the first day of summer, warning of dangerous heat and humidity from Sunday afternoon to Tuesday night. Daytime highs are expected to reach 30 C - 36 C, which will feel like 40-45 with humidex. Meanwhile, overnight temperatures will provide little relief from the heat, as the weather agency is anticipating lows of 21 to 25 C.

“The first significant heat event of the season with dangerously hot and humid conditions will begin Sunday afternoon and is expected to continue into the week,” said Environment Canada.

The weather agency says the heat warning may continue into Wednesday.

“A cold front is expected to push through the region late Tuesday but there is some uncertainty with how far south this front will get. Should it remain farther north, the heat event may continue for Wednesday primarily for southwestern Ontario and the GTA,” said the weather agency.

Extreme heat can be dangerous as it causes heat exhaustion and strokes. Environment Canada is asking people to take extra precautions and to protect themselves.

The early signs of heat exhaustion include headache, nausea, dizziness, thirst, dark urine and intense fatigue. If you suspect you’re affected by extreme heat, stop your activity and drink water.

In case of a heat stroke, you should call 9-1-1 as it’s considered a medical emergency.

The weather agency says you should limit direct exposure to the sun and the heat and schedule your outdoor activities during the coolest parts of the day.

“Never leave people, especially children, or pets inside a parked vehicle. Check the vehicle before locking to make sure no one is left behind,” said Environment Canada.

More information about how to protect yourself from the heat is available online.

Weather forecast

Cloudy skies, showers and a risk of thunderstorms are in the forecast for Ottawa this Sunday.

Environment Canada calls for a high of 31 C, humidex 42, a 40 per cent chance of showers and a risk of thunderstorms late this afternoon.

A low of 21 C and partly cloudy skies are expected for tonight.

On Monday, the capital will see a high of 36 C, which feels like 46 with humidex, and a mix of sun and cloud. A low of 23 C and clear skies are anticipated overnight.

Tuesday day will see a high of 34 C and a 40 per cent chance of showers. A low of 20 C and cloudy periods are anticipated for the night.

The average temperatures for this time of year are a high of 25 C and a low of 15 C.