TorontoForecast.com - Blog

What an amazing day! With unstable airmass induced by a moisture-laden atmosphere and lake breezes, the Greater Toronto Area was pounded by impressive thunderstorms today. Thunderstorm watches and warnings were issued for most of Southern Ontario and Toronto is one of the worst hit area. Toronto Pearson International Airport recorded a wind gust of 98 km/h at 1832 EDT.

Here at Toronto East York (Sunnybrook area), three distinct cells hit the area with the worst one occurred around 1400 EDT. Here are the radar images when the main cell hit our station (indicated by the temperature reading of 76 deg. F):

Here is another radar view:

The table below shows the weather conditions during the storm:

Note that for 10 full minutes, the rainfall rate was in excess of 100 mm/hr. For two minutes, the rainfall rate peaked at 426.6 mm/hr - the highest ever recorded by the Toronto East York weather station. I never experienced such storm before in Toronto - sheet of rain with visibility less than 10 feet, frequent lightning and thunder and pea-sized hail.

It was also unusually dark. The solar radiation reading dropped from 800 W/m2 to 139 W/m2 in one minute (1555 EDT to 1556 EDT). The reading dipped to 84 W/m2 at 1606 EDT during the heavy deluge.

We received 26.0 mm of rain in 20 minutes - another extreme record. You will also notice that the pressure dropped significantly during the storm and winds gusted to 37 km/h.

In fact, the storm was so severe that I called the weather hot line of The Weather Network and e-mailed Brian Hill of 680 News, Michael Kuss of CityTV and Environment Canada.

Minor cells followed in late afternoon and another strong cell hit the area just before 2000 EDT. Essentially, Toronto was in an outflow boundary - a storm-scale boundary separating thunderstorm-cooled air (outflow) from the surrounding air; similar in effect to a cold front, with passage marked by a wind shift and usually a drop in temperature. Here is the storm track for the evening storm:

A more close-up view of Toronto East York station after the passage of the cell (just north of the East York map marking):

Weather conditions from the evening storm (table and graph):

The peak wind gust was 42 km/h!

Note the drop in temperature and excessive rain for more than five minutes. The peak rainfall rate this time was 202.2 mm/hr.

It’s past 2330 EDT and it’s still raining. The total rainfall so far is 43.6 mm and it’s the most rain we ever got here at Toronto East York in less than 12 hours. I won’t be surprised to surpass the 50 mm before the 0200 EDT, the end of a climatological day.

Stay safe and please feel free to leave a comment.

KLM