Southern Ontario and Quebec are in for a hot, muggy weekend as the temperatures and humidex values are on the rise. The elevated heat and sticky conditions will be accompanied by multiple systems, which could spark thunderstorms in the aforementioned provinces, possibly severe in parts of the former Saturday. Friday's threat will be mostly confined to northeastern Ontario. The heat and humidity will continue to climb beyond the weekend, possibly reaching dangerous and uncomfortable levels. Plus, ample amounts of moisture building in could bring several chances of heavy rain and thunderstorms. What you need to know for the weekend and beyond, below.
FRIDAY: STORMS IN THE NORTH, SLIGHT RISK IN SOUTHWEST
A slow-moving front will continue to creep its way across northeastern Ontario Friday, bringing with it showers and the risk for thunderstorms in the afternoon and evening.
There could also be isolated storms pop up across parts of southwestern Ontario in the afternoon. The risk area will be quite narrow, extending from Lake Simcoe to London.
The GTA and rest of the south will see fair conditions, with just than some cloud cover in the afternoon.
Temperature-wise, daytime highs will be into the upper 20s for most, with extreme southwestern sections possible topping the 30-degree mark. The feels-like values will be into the low- and mid-30s. The heat and humidity will continue to build through the weekend.
As a result, there will be a decent amount of CAPE – Convective Available Potential Energy, meteorological shorthand for thunderstorm potential.
SATURDAY: THUNDERSTORM POTENTIAL SHIFTS INTO SOUTHERN ONTARIO, QUEBEC, SEVERE POSSIBLE
The cold front will finally reach southern Ontario and Quebec Saturday, and is expected to bring showers and thunderstorms in the afternoon and evening hours.
Some could turn severe, with the areas at greatest risk of seeing the potent storms stretching from parts of Niagara region through the GTA, cottage country and into eastern Ontario. There will also be an area in the extreme southwest that could see them.
With the ample moisture in play for the storms to tap into, heavy rainfall will be the main hazard, in addition to strong wind gusts and small hail.
Some of the storms may linger into the overnight hours in parts of cottage country, eastern Ontario and southern Quebec. Once they move out, fog is expected to move in.
Temperatures and humidex values won't change much from Friday, though the extreme southwest will see daytime highs a few degrees cooler.
A secondary system, a warm front, will be pushing into Lake Superior Saturday evening with showers, possibly reaching the Georgian Bay by Sunday morning with precipitation.
NEXT WEEK: MORE SHOWERS, DANGEROUS HEAT BUILDS BACK IN
All this humidity will gradually boost the region's PWAT (precipitable water in the atmosphere), meaning any showers that do spring up will be heavier and longer-lived.
Monday and Tuesday look particularly likely to be a rainy one for many people, particularly from the afternoon into the evening.
Meanwhile, the heat and humidity will continue to build to uncomfortable and even dangerous levels through the week.
The culprit will be a ridge of high-pressure parked by the southeastern U.S. In atmospheric terms, it will have the effect of ushering warmer southwesterly winds up into southern Ontario for several days.
That additional heat and humidity will make for dangerously hot conditions across most of southern Ontario, with astounding humidex values.
With daytime highs hovering around 30°C, the humidity will push the feels-like factor to 40, and even slightly above for the extreme southwest.
When planning for next week, people should expect to have to limit outdoor activities and make active preparations to keep cool.
Check back as we continue to monitor the long-range forecast