October heatwave over - stormy weather expected for Thanksgiving weekend

The last appreciable rainfall in Montreal fell on September 19. Only 0.8mm has fallen at Trudeau Airport since. That all changes this weekend as our heatwave comes to an end, and heavy rain moves in. Some locations will receive a months rainfall in 48 hours. Between 50-80mm is possible for our region.

Rainfall warning in effect for metro Montreal.

UPDATE, Saturday, October 7: Weather warnings remain in place as heavy rain continues to fall across southern Quebec. As of 12pm, close to 65mm had fallen in Montreal, with another 40mm possible. That would bring amounts over 100mm (4 inches), a record for the date. As a result of the prolonged dry period we just experienced, little flooding is occurring so far. The exception is water accumulation on roadways, especially where leaves are blocking sewer grates. Drive carefully.

Our October heatwave will come to an end on Friday, but with potentially one more record to break before it ends. The forecast high Friday is 25C (77F), the record for the date, set in 2005, is 26C (79F). We have a shot at it, but increasing clouds may hold back afternoon temperatures just a touch. This will be the last day of our current remarkable heatwave. Montreal managed another record high on Wednesday, reaching 28.5C (85F), surpassing the 2005 record of 26C (79F). Dozens of records for heat and humidex, as well as warmest minimum temperatures have been established across eastern North America this week. Included in that was the warmest October high temperature for Montreal, dating back to 1871, with Tuesday's high of 29.3C. We will likely establish another record for the warmest overnight Friday, having only dropped to 19C (66F) so far. The record was 16.7C set in 1937. The normal high for October 6 is 15C (59F), but what is "normal" anymore.

The unusual heat is over, and our attention turns to a frontal boundary slowly mowing across Ontario. Ahead and along the front, heavy rain is occurring, along with some thunder. It has been 16 days since our last rainfall for most of us. A trace did fall at Trudeau on Tuesday morning as a few isolated thunderstorms bubbled up. We need the rain and we will get it. Showers and thunderstorms should develop this afternoon in Montreal, transitioning to a steady rain overnight and all day Saturday. Total rainfall amounts between Friday and Sunday for southern Quebec will be in the 50-80mm range. Most regions should absorb the rainfall, but there could be some minor water accumulation and flooding in low lying areas.

Tropical storm Philippe, located south of Bermuda on Friday morning, is forecast to weaken and move across Maine and into central Quebec this weekend, adding deep moisture and gusty winds to our forecast. (NHC)

The frontal boundary and parent low pressure will stall over Quebec on the weekend, maintaining showers throughout Thanksgiving and into next week. Adding to the moisture will be the remains of tropical storm Philippe, located 315 kilometres south of Bermuda Friday morning. Philippe is forecast to become post-tropical and move inland across Maine and into southern Quebec by Sunday.

Along with the rain this weekend, will be gusty winds, up to 50km/h, especially Sunday. Temperatures will be the other big story, falling way back to normal values for early October. The low Saturday morning will be 15C, rising to the upper teens Saturday, falling back to the lower teens late in the day and remaining there Sunday, with a high of 13C (55F) expected. The cooler weather will remain with us all next week.