Severe thunderstorm watch in effect for Ottawa on muggy Tuesday

People wait to cross the street in downtown Ottawa on a rainy day. June 18, 2026. (Brad Quinn/CTV News Ottawa)

The hot, humid weather in Ottawa is bringing a risk of a severe thunderstorm on Tuesday.

Environment Canada has issued a yellow-level severe thunderstorm watch for the capital, saying conditions are favourable for the development of severe thunderstorms that may be capable of producing strong wind gusts, large hail and heavy rain.

• Hourly and 7-day forecast on our CTVNewsOttawa.ca weather hub

“Thunderstorms over eastern and central Ontario are expected to keep tracking southeast today, bringing strong winds, hail and heavy rain,” the weather alert says.

Environment Canada says risks include wind gusts of up to 110 km/h, golf ball-sized hail, rainfall amounts in excess of 50 millimetres, and possible tornadoes.

A weather watch means conditions exist that could develop into severe weather. A warning is issued when severe weather is imminent or occurring.

The yellow level on Environment Canada’s colour-coded scale refers to weather that may cause damage, disruption, or health impacts, with impacts that are moderate, localized and/or short-term. Yellow is the most common form of alert, with orange and red being more severe.

Environment Canada’s weather forecast for Ottawa calls for a prolonged period of very hot conditions, with a high of 30 C on Tuesday and a humidex of 38.

Overnight, expect little relief from the heat, with a low of 22 C, around seven degrees warmer than the average low for this time of year. There is a 40 per cent chance of showers and a risk of a thunderstorm.

Canada Day could see a high of 34 C with a humidex of 45. The forecast includes a mix of sun and cloud and a 40 per cent chance of showers in the afternoon with risk of a thunderstorm.

The heat continues on Thursday with another high of 34 C, and a 40 per cent chance of showers.

Friday’s forecast includes a high of 33 C and a 30 per cent chance of showers.

The weekend still has highs around 30 C, but the heatwave should break by Monday.

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