A multi-day thunderstorm threat spans southern Quebec as heat and humidity build in for the May long weekend. For some areas, this will be the highest humidity felt this year, even after the May heatwave experienced a week ago. While the chance for thunderstorms covers off most of the weekend, the heat and humidity will quickly clear for the holiday Monday, with seasonably cool conditions aligned with high pressure and sun and cloud. More on the timing of the storm threats, below.
A mix of sun and cloud is forecast for southern Quebec for the majority of the day Friday, with the humidity into the low 30s building for Gatineau and Montreal.
"A cold front to the north will start its descent south late in the day and that will be the initiation of thunderstorms in western parts of the province into the evening," says Kelly Sonnenburg, a meteorologist at The Weather Network.
Small hail and strong winds would be the main threats with more organized storms that develop.
The storm risk will then shift south through the pre-dawn hours on Saturday, with some nocturnal or early morning non-severe thunderstorms possible along the front.
A widespread storm threat will target much of southern Quebec, along the St. Lawrence and into the Eastern Townships Saturday afternoon, with the greater severe storm dynamics forecast across the Eastern Townships.
"Clusters of thunderstorms are forecast with even the potential for some isolated supercell development with favourable wind shear present," Sonnenburg warns. "We will need to keep an eye on rotation if stronger supercells do develop."
Large hail, strong winds and heavy to torrential rain are all likely as there will be ample moisture available in the atmosphere, which also contributes to the high humidex values.
Humidex values in the mid to upper 30s are forecast for Saturday.
As a secondary system tracks into the province on Sunday, the thunderstorm threat will return for a third and final day with the risk for strong storms once again along the St. Lawrence and into the Eastern Townships.
Atmospheric moisture will also be high as well, so torrential rain at times will be likely.
Check back as we gather more forecast details on the severe storm set-up for Sunday.
As the thunderstorm risk finally eases, the heat and humidity will also be wiped clean, with dry and seasonably cool conditions left in the wake of the multi-day thunderstorm threat.
Be sure to check back as we continue to fine tune the long weekend storm risks across southern Quebec.