Local amateur weather watcher Dave Brain says the city has been inundated with 35.6 millimetres of rain over the last two hours.
The sudden storm, emerging from a day of sunshine and blue skies, has led to rain-filled gutters, some minor fender-benders and at least one road closure.
The city, at shortly after 7 p.m., said Queen Street has been closed "due to flooding from the recent downpour."
This is an area of the city often hardest hit by sudden storms.
City crews are on site trying to clear the water. Motorists are being asked to steer clear of that area around Front Street.
The city will announce, via their social media channels, when the street is reopened.
It may be a while. Brain said more rain is likely on the way.
Environment Canada seems to agree. Their meteorologists are tracking a severe thunderstorm capable of producing very strong wind gusts, up to nickel size hail and heavy rain.
This cluster of severe thunderstorms is located from Midland to Wasaga Beach east towards Orillia moving east at 50 km/h.
According to a warning issued by Environment Canada at 7:07 p.m., heavy downpours can cause flash floods and water pooling on roads.
Strong wind gusts can toss loose objects, damage weak buildings, break branches off trees and overturn large vehicles. Remember, severe thunderstorms can produce tornadoes. Lightning kills and injures Canadians every year. Remember, when thunder roars, go indoors!
Severe thunderstorm warnings are issued when imminent or occurring thunderstorms are likely to produce or are producing one or more of the following: large hail, damaging winds, torrential rainfall.
The Office of the Fire Marshal and Emergency Management recommends that you take cover immediately if threatening weather approaches.
Please continue to monitor alerts and forecasts issued by Environment Canada. To report severe weather, send an email to ONstorm@canada.ca or tweet reports using #ONStorm.