Meteorological conditions associated with the record rainfall and major flood of July 8, 2013 in Toronto, Ontario

Record rain fell on Toronto during July 8, 2013 and caused flash floods, electrical power outages, stranded cars on roads, and cancelled or delayed flights to or from two major airports. About 1400 commuters were rescued from a stranded commuter train after railway tracks became flooded.

For perspective, the monthly average rainfall for Toronto is 2.91 inches. Toronto Pearson International airport, where official observations are recorded, received 4.96 inches and some parts of Toronto received more than 3.54 inches in a few hours on the afternoon of July 8. The previous record rainfall for a single day was 4.76 inches, on Oct. 15, 1954, caused by Hurricane Hazel.

What caused this unusual and record-breaking rainfall? Examination of upper air patterns, moisture, precipitable water, surface pressure patterns and other factors shows that this event is entirely explained by ordinary, although uncommon, meteorological conditions.