During the week of July 12 to 18, 2023, the overnight forecast for Montreal is a low of 20 degrees Celsius. In comparison, the seasonal normal for this week should be 17.1 degrees Celsius instead.
We are talking about a planned difference of almost three degrees in minimum temperature, which has the effect of creating uncomfortable nights.
A growing trend
These crushing nights of heat and humidity are nothing new. In fact, this phenomenon has been on the rise in Quebec for years.
In Montreal, the number of warmest nights in July has increased over the past decades. Between 1961 and 1990, there were an average of 84 nights when the mercury indicated temperatures above 20 degrees Celsius, compared with 127 nights between 1991 and 2020.
The observation is the same in the Gatineau region, where the figures have increased dramatically, nearly doubling. In July from 1961 to 1990, 66 nights above 20°C were recorded. In the second period analyzed, from 1991 to 2020, no less than 123 nights above 20°C were calculated.
Why is it so hot at night?
The main reason for this nocturnal phenomenon is the present high level of atmospheric humidity. This reduces hot nights and body chills.