Poor air quality forecast for southern Quebec Sunday

Widespread smoke and poor visibility is set to return to southern Quebec into Sunday. Numerous wildfires are burning out of control across northern Saskatchewan and Manitoba. The smoke has resulted in air quality alerts being issued across Ontario and Quebec as well as the Great Lakes, Upper Midwest, New England and the northeastern US.

Air Quality Alert for the entire region.

Gusty westerly winds are expected to carry wildfire smoke from western Canada into the lower levels of the atmosphere in Montreal and Ottawa this evening and especially Sunday. An AQI reading greater than 100 will result in very unhealthy air for any outdoor activities. The smoke will be widespread across southern and eastern Ontario, southern Quebec as well as New York and New England. Poor air quality from fine particulate matter related to fire smoke, can result in burning eyes and nose as well as difficulty breathing.

Strong high pressure is expected to slowly drift across southern Quebec over the next few days, providing our region with dry weather well into the upcoming week. Gusty west winds and low relative humidity levels will increase the fire risk across the region. The Montreal region has had less than 1mm of rain over the last 16 days. The dry weather has been accompanied by very warm temperatures at times, with 9 days over 30C (86F) recorded at Trudeau Airport during the month of July.

Montreal also managed 138mm of rain, well over the normal amount of 91mm. Most of that fell during the flash flooding of July 13, when a new July monthly record of 81.6mm fell at the airport. That included 22.4mm in just 15 minutes. The intense rainstorm erased the July 10, 2024 record of 79.2mm.

So for the upcoming week, we are looking at smoke clearing by Monday, with sunshine and clear nights. High temperatures will be in the upper 20s to near 30C, with overnight lows in the middle teens. No rain is expected through next Friday.

Heat warning for Montreal - followed by fall-like stretch of weather to begin August

A towering thunderstorm over Pincourt last Thursday, July 13. The storm produced torrential rain, but thankfully was quick moving, alleviating the flood risk. More strong storms are possible this Thursday and again next Tuesday, before much cooler weather arrives to start the month of August in Montreal. (Valley Weather Photo)

Environment Canada has issued a heat warning for southern Quebec for Thursday, with high temperatures expected well into the 30s, and humidex readings approaching 40C (104F) in Montreal during the afternoon hours.

The hot weather is part of an expanding heat dome that has resulted in widespread weather warnings across a large portion of the central and eastern United States and into southern Canada. Along the circumference of that heat dome, heavy thunderstorms have been occurring through the Dakotas, upper Midwest and Great Lakes into parts of Ontario.

For Montreal, we can expect a very warm and humid Thursday, with a forecast high of 33C (91F). Clouds will increase late in the day as a cold front advances into the St. Lawrence Valley from central Ontario. Showers and thunderstorms are likely, persisting into Friday. Some may be on the stronger side, with heavy rain and gusty winds possible.

Friday will be a little cooler, with daytime highs in the middle 20s. The heat will build again Saturday though Monday, with highs once again near 30C (86F). Overnight lows will be in the upper teens to near 20C.

By Tuesday, a more potent cold front will result in another round of showers and thunderstorms. Finally high pressure moves into southern Quebec to end the month and start August, with much cooler weather expected. Highs will drop into the lower to middle 20s for many locations, with overnight lows in the lower teens and even some single digits. The early taste of Autumn for Montreal will prevail during the first week or so of August. 

Stretch of near-perfect summer weather for Montreal

Skies cleared on Sunday afternoon, providing ideal weather for the annual car show at Pointe-du-Moulin in Notre-Dame-de-L'Ile-Perrot. Unfortunately the threat of morning rain resulted in lower numbers of cars on display and patrons attending.
(Valley Weather) 

Monday will be as perfect a summer day as you can expect in Montreal in July. High pressure building in behind Sunday's cold front, will result in nothing but sunshine, low humidity, cooler temperatures and smoke-free skies. Highs will be in the low to middle 20s, cooling back into the lower teens by Tuesday morning, with even a few single digits possible outside the city. Winds should remain light.

This ideal summer weather will persist through Wednesday, before heat and humidity being to build again. Active weather returns by Thursday as higher humidity levels and warming temperatures nearing 30C (86F), will result in numerous showers and thunderstorms. The muggy weather will continue into Friday.

Morning showers drift to the south as skies clear Sunday afternoon on Ile Perrot. A lone ship travels Montreal bound through the St. Lawrence Seaway on Lac St Louis. (Valley Weather Photo)

Over this past weekend, we had a few showers late Saturday into Sunday, but the front proved to be rather unimpressive for southern Quebec, a welcome relief after the flash flooding and thunderstorms of the past week. For the short-term, the hot and humid air has settled back south into the central and southern US, where millions are under heat advisories. Strong high pressure in those regions has resulted in a heat dome dominating the weather. Temperatures will soar into the middle and upper 30s, with humidex (real feel) readings over 38C (100F).

Along the periphery of the heat dome, slow-moving strong thunderstorms will continue to produce heavy rain and thunderstorms, in what is quickly becoming the summer of the flash flood across North America.

For now, that weather will remain to the south of Montreal and the St. Lawrence Valley. By next weekend, we are looking at pleasant weather once again, with perhaps the hot and humid weather pushing back north for the final days of July.

Much needed break from the heat and humidity for Montreal

Thursday's strong thunderstorms approach the Island of Montreal off Lake of Two Mountains during the late afternoon. (Valley Weather Photo)

A fresh and cool air mass has descended upon Montreal Friday morning, a welcome relief from the oppressive heat and humidity of the past week. We had one more steamy day on Thursday, with a high of 30.6C (87F) in Montreal. It was the third 30C plus day in a row and 7th this month. Many of those days have had elevated dew points and humidex readings near 40C. So far this summer, Montreal has recorded 12 days warmer than 30C (86F), with 6 days just under at 29C (85F).

A strong cold front swept across the southern portion of the province, producing waves of heavy thunderstorms. Thankfully the storms were fast moving, and that managed to limit the flood potential, at least in Montreal. Trudeau Airport measured 26mm, bringing the monthly total to a very wet 135.2mm. Strong winds accompanied the storms as well, with a gust to 74km/h at Trudeau and 89km/h at Saint-Hubert.

A flooded delivery car on a highway near Quebec City Thursday afternoon. An image all too familiar to Montrealers. Between 75 and 85mm of rain fell on the provincial capital in under two hours causing significant flash flooding. (TWN)

While we escaped the flooding this time, Quebec City did not. Both Levis and Sainte-Foy reported significant flash flooding after 75-85mm of rain fell in under two hours. Roads were inundated with many water rescues taking place. Many homes and businesses sustained significant flooding as well. 

The good news is that we are in for a cooler stretch of weather. After a refreshing morning low of 15C (59F) on Ile Perrot, we can expect daytime highs around 24C (76F). Saturday ooks perfect as well, with sunny skies, low humidity and a high of 25C (77F).

Low pressure will skirt along the international border for Sunday, with light rain forecast, perhaps around 10-15mm. Next week will start off cool and dry, before the heat builds again for the second half of the week.

Strong thunderstorms possible Thursday - cooler weather returns Friday

Strong thunderstorms, some with heavy rain are possible again on Thursday, but at this time we are not expecting a repeat of the widespread flash flooding that occurred this past Sunday. (Photo: Domenic Fazioli)

6AM: Severe Thunderstorm Watch posted for metro Montreal.

Heat Warning remain in effect. Expect thunderstorms today, with strong winds and heavy rainfall possible.

The heat warning remains in effect for one more day across southern Quebec, but cloud cover and thunderstorms should keep our high temperatures under 30C Thursday. Trudeau Airport reached 32.6C (91F) on Wednesday, with a record overnight low of only 25.4C (77F). 

The end of the current heatwave is in sight, as a strong cold front is forecast to sweep across eastern Ontario and southern Quebec Thursday. In advance of that front, temperatures will warm to 29C (85F) in Montreal today. Some isolated storms are occurring this morning, but stronger, more widespread activity is likely this afternoon.

ECCC thunderstorm outlook for Thursday. Strong thunderstorms are possible in Montreal and across southern and eastern Quebec, with gusty winds the main threat.

At this time, we are not looking at a repeat of Sunday's flash flooding that occurred across the city, but some of the storms could be severe, with strong winds being the main threat. A few cells may have heavy rain, but they are expected to be moving faster than the weekend activity, therefore lowering the flood risk for Montreal. That being said, there could still be some localized water accumulation, so listen for any weather watches or warnings that may be issued later today.

A few storms may be strong enough to produce an isolated tornado or two. The main risk area would be in eastern Ontario from Ottawa towards Cornwall, Upstate New York and Vermont, as well as the Eastern Townships and Beauce regions closest to the American border.

Outside of the thunderstorms, expect another warm and humid day, with gusty southwest winds in the 30-50km/h range. Those winds will back to the north tonight.

Overnight, a refreshing air mass will arrive, with lowering temperature and humidity levels. By morning, lows may be in the lower teens. Friday will be a spectacular summer day, with sunshine, low humidity and a high of 24C (76F). Saturday will be sunny and pleasant as well, before showers return for Sunday.

After the flood - heat and smoke settle across southern Quebec

A film of haze and smoke from western Canadian wildfires lies across the Montreal skyline early Tuesday morning. Montreal is reporting some of the poorest air quality on the planet today, with some improvement forecast by Wednesday.

Air Quality Advisory and heat warning are in effect for southern Quebec.

After the flood comes the fire. Montreal has some of the poorest air quality in the world early Tuesday morning, as smoke from western Canadian wildfires drifts into the lower atmosphere over southern Quebec. 

As of 7AM, Trudeau Airport was reporting an unhealthy Air Quality Index (AQI) of 152, which places it 5th in the world among major cities for polluted air. We are also 5th in Canada, just ahead of Ottawa and behind Saskatoon, which has a very unhealthy reading of 239.

Combine that with elevated heat and humidity today. High temperatures will approach 32C (90F), with humidex values near 40C (104F). What does all this mean? Try to limit your outdoor activities, especially during the afternoon hours. This type of weather impacts the very old and young, as well as those with existing repository or other health concerns. The fine particulate matter from the smoke can cause difficulty breathing as well as eye, nose and throat irritations. In the worse cases, the smoke can impact breathing.

The smoke should ease later today in Montreal, but the high heat and humidity will intensify into Wednesday and persist through Thursday before relief comes in the form of a cold front. Wednesday will be the warmest day in this stretch, reaching 34C (94F). Overnight lows will be around 21C (70F).

Thursday's cold front will be accompanied by showers and thunderstorms. as with Sunday, some may be on the strong side, but that will depend on the time of day the front arrives in Montreal. Details to follow as the event draws closer.

Behind the front, much cooler, less humid air will arrive Friday, giving Montreal a much-needed break from the oppressive heat. The high Friday is forecast to be 26C (79F), and more importantly, morning lows will drop into the lower teens.

We are watching the development of what should become Tropical Storm Dexter. The system is expected to cross over the northern portion of Florida over the next day or so, before strengthening in the Gulf of Mexico. The system is expected to be a big rain maker across portions of the southern US and bears watching.

For now, stay cool.

Déjà vu all over again as flooding sweeps Montreal

Montreal experienced significant flash flooding once again, as strong thunderstorms swept across the city Sunday afternoon. The result was 50 to 100mm of rain in under 2 hours, overwhelming sewer and drainage systems. Several motorists became trapped by rapidly rising flood waters and a number of highways were closed. (Radio Canada)

Hot, humid and smokey weather expected this week in Montreal, with more thunderstorms possible. 

Heat Warning in effect for Montreal. 

Round after round of heavy thunderstorms Sunday afternoon dumped between 50-100mm of rain on the city creating widespread flash flooding once again. This is the third time in a year that Montrealers have had to deal with rising flood waters.

Sunday's flooding was courtesy of a warm, humid and unstable air mass that had been in place for several days. Introduce a frontal boundary from Ontario tapping into deep Gulf of Mexico moisture   and you have the ingredients for slow moving, very wet thunderstorms.

Strong winds and intense lightning accompanied the storms, snapping power poles along Route 138 near the Town of Mercier in the Montérégie. Over 35,000 Hydro-Québec customers lost power during the storms. (Spotted Chateauguay)

On Ile Perrot, between 2-4pm, I measured 55mm of rain. On the West Island and at Trudeau Airport, 81.7mm fell, a record for the date, surpassing the 38.6mm that fell in 2023. Some parts of north end Montreal had as much as 110mm.

The heavy rain overwhelmed the sewers once again in Montreal, flooding major highways, surface streets and scores of businesses and home from Lachine to Saint-Léonard to Kirkland and everywhere in between.

Sections of Highways 13-15-20 and 40, along with ramps and several underpasses had to be closed for varying amounts of time so vehicles could be removed and flood waters cleared.

Insurance adjusters will be out again surveying the damaged to homes as many basements flooded across the Island.

Over 35,000 Hydro-Quebec customers loss power as lines were impacted by falling tree limbs and intense lightning strikes. The storms had far-reaching effects, from south of Montreal in the Monteregie where power poles were snapped like toothpicks, to Mirabel and parts of the Laurentians where flooding was reported.

The storms come close to the July 14, 1987 anniversary of the Decarie flood. That storm officially dumped only 57.4mm of rain at Trudeau Airport, but amounts as high as 100 mm were reported in less than 1 hour in other parts of the city.

History keeps repeating it seems in Montreal. July 14 marks the 38th anniversary of the great Decarie Expressway flood.

The weather will remain very warm and humid this week, with unfortunately another risk of strong thunderstorms by Thursday. The air will also become quite unhealthy, as smoke from the western Canadian wildfires drifts into Ontario and southern Quebec.