Hot, sticky start to summer spurs humidex advisory for Ontario, Quebec

While the beginning of summer brought heavy rain and flooding to Alberta, a heat-wave to the Yukon and storms to Saskatchewan and Manitoba, a mixture of heat and humidity has been brewing over southern Ontario and Quebec that promises to make the first half of the work-week sweaty, sticky and smoggy.

Temperatures in southern Ontario — from Windsor to Peterborough — had already topped 30 degrees C on Sunday, with humidex values pushing 40, and these conditions are expected to not only continue through Monday, Tuesday and Wednesday, but also spread to impact further north, through the Georgian Bay and Algonquin areas, and into eastern Ontario and southwestern Quebec as well.

Environment Canada has issued a humidex advisory for the next few days, and while the Ontario Ministry of the Environment's Air Quality Office is currently forecasting Moderate air quality, hot, sticky, stagnant weather is typically the perfect 'breeding ground' for smog, so air quality conditions could get worse as this weather persists.

[ More Geekquinox: How weather, geography made Alberta a target for flooding ]

With hot and humid weather patterns like this comes the risk of severe thunderstorms late in the day and into the evening. You might be familiar with them as 'pop-up thunderstorms', although the more technical term is 'air mass thunderstorms' — so called because they form without the help of a weather frontal system to spur them along. As this video shows, these storms can be quite strong, and they typically pass fairly quickly.

These familiar afternoon/evening storms are generally caused when the hot summer sun heats the ground to a point where it creates strong updrafts of rising air above it. As the air rises, the water vapour in the air that makes it feel so sticky for us starts to condense into water droplets, forming a cloud. The act of forming the cloud actually releases more heat, making the air within the growing storm cloud less dense than the air around it, making it rise even further — and this sets up strong updrafts in the cloud that can quickly turn it into a towering thunderhead. Along with the updrafts come strong downdrafts that can make for harrowing aircraft landings, and even create downbursts and spin up tornadoes.

(Photo courtesy: Michelle Siu/Canadian Press)

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