Heat wave continues with possibility of thunderstorms in Waterloo region, Guelph and area on Tuesday

Waterloo region has broken two 102-year-old weather records in the last two days and the heat is expected to persist for much of Tuesday.

• On Sunday, the temperature hit 33.3 C, which broke the record of 32.8 C set on June 22, 1923.
• On Monday, the temperature rose to 34 C by 4 p.m., which broke the record of 33.3 C which was set on June 23, 1913.

But while the record for the hottest June day ever — 36.7 C on June 28, 1944 — is unlikely to be broken this time around, Environment and Climate Change Canada meteorologist Geoff Coulson says the heat will continue Tuesday and bring with it some unsettled weather.

"We may have the chance of some shower and thunderstorm activity popping up later in the day and then through the evening hours. Some of these storms may potentially be strong," Coulson said, reminding people to watch the weather forecast throughout the day as a thunderstorm watch or warning could be issued.

Coulson says the hot weather may have surprised people, especially after June saw some warm days, but not much in terms of humidity.

"This was the first heat warning heat event of the season and also record-breaking," he said, noting heat warnings can be issued that don't necessarily break records.

"The combination of record-breaking temperatures, very high levels of humidity leading to humidex readings approaching the low to mid 40s, even someone in relatively good shape in these types of conditions, if they're doing any type of activity outside, is going to feel it."

Coulson said people vulnerable to heat, such as the elderly, very young, people with medical conditions or those who may find it difficult to get out of the sun into a cool space means "the impacts were felt" by a lot of people.

"It can be a bit deceptive," he said of the heat and its effects on a person's body.

"The other thing they talk about is even just the thirst reflex doesn't necessarily provide you with enough of a tap on the shoulder to drink as much as you should be — that you are losing a lot of moisture through sweat in these conditions. You really need to make sure you're staying hydrated."

Wednesday will still be warm, not as humid

The heat warning remains in effect for Waterloo region, Guelph and Wellington County on Tuesday.

It's expected to be a sunny day with a high of 32 C and a humidex value of 40 C. The UV index is 10, which is considered very high.

The forecast says there is 30 per cent chance of showers and a risk of a thunderstorm in the afternoon.

Coulson says there could be some relief late Tuesday and overnight into Wednesday as the overnight low drops to 15 C.

Wednesday will be "a warm one" but not as humid. 

"Likely Wednesday we'll see the end of the heat warning or they may end it overnight Tuesday night into Wednesday morning if we drop down to that 15 C or 16 C for the overnight low," he said.

Hot summer ahead

Environment and Climate Change Canada's summer forecast has said Ontario can expect a hotter than normal summer this year.

In a press conference on June 10, warning preparedness meteorologist Jennifer Smith said statistically, the above-average warmth may be skewed by extreme short-term heat waves. 

But in other cases, "it could be recurring short warm spells or just a subtle, consistent warmth that pushes seasonal averages up enough to nudge the stats."

Caroline Metz is the managing director of the Intact Centre on Climate Adaptation at the University of Waterloo. She says people in the cities may feel the heat more than those in rural areas.

"Our buildings and our roadways, they're made of materials that tend to absorb heat during the day and then they radiate it at night. And then we get waste heat from vehicles, from buildings. We generally have less trees and water features in cities," Metz said Monday on the CBC Radio noon-hour call-in show Ontario Today.

She said as people plan for a warming climate, there are steps they can take.

"We want to make sure that our homes, our schools, our buildings, they have energy efficient cooling available and then they're also designed or upgraded with good insulation, shading on windows, reflective or light coloured roofing materials, lots of other features that can help naturally support a cooler indoor living space," Metz said.

She noted for people who are working outside it's very important to take breaks throughout the day.

They should be "staying in the shade, drinking lots of water — very, very important — and let someone know if you're not feeling well," she said.