Around mid-day on May 21, dark clouds eclipsed Ontario skies, unleashing torrential rain and howling winds. In its wake, it left behind fallen trees, damaged homes, and widespread power outages. The culprit is what experts call a derecho storm.
Derecho, a Spanish word meaning straight ahead, is a long-lasting, fast-moving thunderstorm that can unleash winds as fast as a tornado. Unlike a tornado, a derecho’s winds don’t spiral. Instead, they blow in a straight path.
“When it becomes extreme, the wind speeds start to exceed 100 to 110 kilometres an hour, and they last for 600 kilometres or more,” explained Peter Kimbell, an Environment Canada meteorologist. Derechos are caused by the downdrafts from thunderstorms. This particular storm was caused by a heat dome over the eastern U.S.
Kitchener recorded the highest measured wind speeds at 132 kilometres per hour, but Kimbell says it’s likely winds reached even higher speeds in areas where there weren’t measuring devices.
After analysing data collected during the storm, the Northern Tornado Project (NTP), a research group based out of Western University, hypothesized that the worst-hit areas appeared to be Ottawa, Uxbridge, and London. Based on the group’s data, the NTP says it believes wind speeds reached 190 kilometres per hour in Ottawa, creating a five-kilometre-wide path of intense damage.
Both Uxbridge and London experienced tornadoes, according to the NTP. In Uxbridge, the tornado touched down around 1:15 p.m., travelling 4.26 kilometres and reaching a max wind speed of 195 kilometres per hour. The rooves of two apartment buildings were torn off.
In London, two tornadoes touched down. The first occurred at 11:36 a.m., travelling 5.6 kilometres through the northeast section of the city, reaching a max wind speed of 160 kilometres per hour, damaging an airport hangar door and flipping over a plane. The second tornado touched down in the south section of the city at 11:39 a.m., travelling 3.4 kilometres and reaching a max wind speed of 175 kilometres per hour.
And this is only what’s been recorded so far, Kimbell says. “Undoubtedly, there is damage elsewhere in cottage country that probably was equivalent, or maybe even greater, but we don’t know because we haven’t been there to find out.”
The storm left over 650,000 Ontario residents without power, according to Hydro One. In a statement released on Thursday, the company said that it “anticipates power will be restored to 99 per cent of customers affected by the storm by Friday evening. Due to the severity of damage, some customers in rural, remote, and island locations in the Perth and Bancroft areas will be without power for several more days. In the Tweed area, a small number of customers may be without power for several more weeks due to the extraordinary level of damage.”
The storm took down 1,900 hydro poles, broke 300 hydro pole cross arms, and damaged 200 transformers. Hydro One has 3,200 people working to repair the necessary infrastructure, including out-of-province and international contractors.
“When rebuilding after a storm, Hydro One prioritizes restoration to bring power back to the greatest number of customers in the shortest period of time. Crews need to repair and rebuild main power lines along with other key pieces of infrastructure before repairs can be made to power lines that serve a smaller numbers of customers,” the company said.
Right before the storm hit, Environment and Climate Change Canada broadcasted a severe thunderstorm warning to people’s cellphones across Ontario. According to ECCC, to warrant a wireless alert, there either needs to be a tornado warning or a thunderstorm exhibiting wind gusts of 130 kilometres per hour or greater, or baseball-sized hail (seven centimetres) or greater.
This was the first derecho to hit Ontario since 1999. While Kimbell says he can’t speak to whether climate change will increase the frequency of this type of event, he does point out that there has been no increase in thunderstorms, which cause derechos, across the country in the last 20 years. “We do get these nasty events every now and then. But we don’t see an increase of thunderstorm activity so far.”