Sunday, May 21 marks 70 years since a deadly tornado devastated downtown Sarnia and made its way toward Middlesex County.
In 1953, a storm crossed the St. Clair River and resulted in the deaths of seven people, five were Ontarians. It came ashore at 6:45 p.m. at Ferry Dock Hill.
"The tornado itself touched down in Smiths Creek, Michigan and it moved to the east-northeast," said Environment Canada Meteorologist Brad Rousseau. "It's a fairly common path we see with storms that develop and impact the southern Ontario region."
Lambton County's past emergencies website notes the tornado as an F3, but Rousseau said their records show it was actually an F4.
"The way the F scale works, it basically gives a rating based on damage and they can roughly estimate the wind speeds associated with the damage," Rousseau said. "So essentially, the difference between an F3 and F4 could be a house being mostly destroyed versus a house being completely destroyed and taken off its foundation for example, that's kind of the biggest difference there."
The tornado damaged nearly 100 buildings in the city's downtown and forced about 500 people to leave the area. Overall, the tornado was on the ground for two hours and 39 minutes.
Rousseau said although the storm's track was fairly common for this area, an F4 in the region is where the rarity comes in.
"Since records began, we have records that started back in the late 1700s and in total, for the entire province of Ontario, there's only been 11 F4s ever documented," he said. "These types of storms, these types of tornadoes of this strength are incredibly rare in Ontario -- across North America for that matter."
Rousseau said the last confirmed F4 to hit southern Ontario would have been the Barrie and Grand Valley tornadoes, which both occurred on May 21, 1985.
Although F4s are rare, the fact that 11 have been confirmed in Ontario shows that they can happen, so Rousseau said it's important for residents to have an emergency plan in place just in case.
Technology has come a long way since 1985, however, Rousseau said detecting these types of storms is still "incredibly difficult."
"There are certain implications in terms of how close a storm is to the radar and things of that nature to be able to more readily detect that rotation on the lowest levels, but certainly there have been improvements in both technology and just our basic understanding as well to the environments that conducive to these types of events," he said.
Earlier this month, another storm anniversary was marked. As of May 2, it's been 40 years since an F4 tornado touched down in Reeces Corners.