Significant heatwave to impact southern Quebec

A significant heatwave is expected in Montreal though late next week. High temperatures are forecast into the middle 30s, with overnight lows remaining warm in the low to mid 20s. High humidity levels will make it uncomfortable and dangerous at times.(AccuWeather.com)

Friday will be the first day in a week long heatwave forecast for much of eastern North America. Warm high pressure will move from the upper Midwest into the Great Lakes and slowly across Quebec and New England over the next few days. Heat and humidity will start to build on Friday in Montreal, with the warmest days expected Sunday through Tuesday.

A dangerous combination of high temperatures and humidity will see daily humidex values ranging from the upper 30s into the middle 40s. Heat warnings and advisories have been posted for a wide area of Ontario and the Ohio Valley into New York and New England. Those should be extended into southern Quebec today or Saturday. Records should fall in many locations. The warmest day ever recorded in Montreal was 37.6C (99.7F), August 1, 1975. We have a slight chance of equaling that during this heatwave.

As far as practical weather is concerned, we will have hazy sunshine most of the time. As the warm air advances into southern Quebec, an area of thunderstorms is expected on the periphery of the air mass. These may affect Montreal as early as Friday afternoon. There is also a risk of storms Saturday afternoon, and Monday through Thursday of next week. High temperatures will range from 30C (86F) on Friday, up to 36C (97F) Canada Day and Monday. The balance of next week will remain very warm, with slightly more cloud cover and thunderstorm activity, look for highs of 32C to 35C (90 to 95F). Overnight lows will remain very warm, especially in urban areas, between 21C to 24C (70 to 75F).

It is important to be vigilant during heat of this intensity. Heat stroke can occur very quickly. Stay hydrated, avoid overexertion during the peak heating hours. Pay close attention to the very young and old. Walk your pets in the early morning hours or late at night. Cars and heat do not mix as we have tragically seen this summer in Montreal. Children and pets should only be near vehicles with you, and ideally with the air conditioning on. Try to conserve energy during peak morning and afternoon hours, avoid running large appliances other than the A/C.

Stay cool and stay safe. Happy Canada Day!