Yesterday's thunderstorms dumped a whopping 126 mm (5 inches) of rain at Toronto's Pearson International Airport in just a few hours, breaking the old one-day record of 121.4 mm set on Oct. 15, 1954. Records at Toronto Pearson began in 1937.
The BUF radar below shows the total doppler estimated rainfall for the event in inches. As you can see, the heaviest rainfall was just west of downtown Toronto and out toward the airport and Brampton.
The big difference between the above-rainfall events was that the 1954 event was associated with the remnants of Hurricane Hazel, while yesterday's event was slow-moving thunderstorms.
By the way, Toronto city airport received 97 mm (3.82 inches) yesterday.
Why did it rain so much?
Looking back at the surface and upper-level data, along with radar there are a few explanations.....
1. Unusually high dewpoint air (high humidity) has been in place across the region with a tropical origin (direct from the Gulf of Mexico and Caribbean).
2. Surface winds were converging around the Greater Toronto Area for several hours as the lake breeze was meeting up with the westerly land breeze. As the warm, humid air converges, it is forced to rise. As it cools higher in the atmosphere, it condenses as clouds then rainfall. This convergence helped feed the thunderstorms that approached the area.
3. The winds aloft that typically steer a thunderstorm were weak, thus the storms were very slow-movers and were able to dump a lot of rain in a short time.
Questions or comments?
Feel free to email me right here.
You can also follow me for storm updates on my twitter @BrettAWX. It was quite busy last night!
I will discuss the new long range forecast monthlies later today.
Mild air masses likely to outnumber the chilly air masses for a good part of October.
Jet stream pattern across North America will become amplified across North America into next week, which means more extremes in weather.
Warm weather will dominate in the eastern half of the country for the next week. Pattern change possible during the last week of September.
The jet stream will strengthen from the Pacific across southern Canada over the next 1-2 weeks which will keep any sustained chilly/cold air masses up across western Alaska and eastern Siberia.
The latest clues to the long range into the month of October.
Late-season heat in the East and mountain snow in the West. Welcome to the fall season!