More heat, humidity and thunderstorms

High humidity levels have produced hazy skies over Montreal since the flooding last Wednesday. Adding to the hazy skies has been high altitude smoke from wildfires burning in western Canada. Expect a few more days of hot and humid weather, along with scattered thunderstorms and the potential for more local flash flooding.

Typical July weather will persist across southern Quebec, as we remain on the northern edge of a very hot and humid airmass along the eastern seaboard and central portion of the United States. We can expect elevated humidity and temperatures near 30C (86F) through Wednesday. Humidex values will be close to 40C for many locations. 

Heat warnings have been issued for eastern Ontario, and heat advisories for the Champlain Valley of Vermont and New York. Regardless of the warnings, the weather will feel muggy and oppressive, so seek out A/C or a pool and drink plenty of fluids over the next few days.

There is a risk of pop up thunderstorms during the afternoon and evening hours, the greatest risk being Wednesday along a cold front. Any thunderstorm that develops in this type of airmass, has the potential to produce heavy rain and flash flooding. We experienced just how quickly flooding can happen in Montreal last week, with just 50 or 60mm of rain falling in an hour or two. Other than the rain, there is a risk for small hail and strong winds, even perhaps an isolated tornado away across the lower Laurentians and in the Eastern Townships.

July has been a warm month in Montreal, with 29C (85F), being the magic number. Trudeau Airport has reached 29C on 8 days this month, with 30C (86F) on three of the other days of the 15 so far. Humidity levels have been sweltering at times, with plenty of moisture around, as 89mm of rain has already fallen in July. As I write Monday morning, we are already sitting at 24C (76F), with a tropical dew point of 21C (70F), humidity reading of 83 percent and a humidex value of 33C (92F) at 8AM.

By Wednesday, cooler, less-humid air should arrive across southern Quebec as a cold front moves across the St. Lawrence Valley. Showers and thunderstorms will accompany the front into Thursday before skies clear for Friday and into next weekend.