Atlantic Canada Weather Blog: Convective Outlook Valid for Today, Tonight and Tomorrow

Regional Impacts

NB… Slight chance for some isolated thundershowers this afternoon and evening. Main threat is locally heavy downpours of 10 to 20 mm/h.

NS/PEI/NL… None.

Convective Discussion…

An upper low currently sitting over the St. Lawrence Valley will be the main trigger for convection today. The low will slowly begin to move east this afternoon, with convection expected to fire in Maine before crossing the border as the low moves into western New Brunswick. Instability is expected to be quite limited today, with only up to 500 J/kg of MLCAPE forecast this afternoon. Modest bulk shear of 15 to 25 knots should inhibit most storms from becoming too organized, so severe weather is not expected today. Nonetheless, the upper low should be enough to fire a few weak thunderstorms later this afternoon in western New Brunswick once convective temperatures (20 C) are reached, with locally heavy downpours of 10 to 20 mm/h being the main risk.

This low will continue to move east tonight, to lie over Anticosti Island by tomorrow afternoon. As such, most of the convection will be centred over the Gulf of St. Lawrence tomorrow. As the low moves into the Gulf early tomorrow morning, relatively warm waters of 18 to 20 C in the area of interest, and the cold upper low, should provide enough instability and vorticity for convection. With this, there exists a slight chance for a waterspout off the Acadian coast of New Brunswick in the morning hours.

Thunderstorm Outlook for Today