Regional Impacts
NL… Some scattered thunderstorms across central Newfoundland this afternoon. Main hazards are rainfall rates of 20 to 30 mm/h and wind gusts of 60 to 70 km/h.
NB… Elevated thunderstorms possible tonight with rainfall rates of 15 to 25 mm/h. Scattered thunderstorms over southern New Brunswick possible tomorrow with rainfall rates of 25 to 50 mm/h.
NS/PEI… Isolated thunderstorms possible tomorrow over northern and central Nova Scotia and eastern PEI. Main hazard is torrential downpours of 25 to 50 mm/h.
Convective Discussion…
Today, most of the convective activity will be associated with a trough moving through Newfoundland. Some clearing behind the initial convection this morning will allow MLCAPE values to rise to 1000-1500 J/kg by this afternoon. Bulk shear values near 30 kts will aid in organising this convection as it moves east through central Newfoundland this afternoon. One of the limiting factors today will be the amount of upper and mid level cooling, especially over southern Newfoundland. Thus the main area of interest this afternoon will remain in central and northern Newfoundland as the trough moves through. The main threat with these storms will be locally heavy downpours of 20 to 30 mm per hour, but strong wind gusts and some pea sized hail are also possible. A few isolated thundershowers are also possible over southern Labrador today, however these storms are not expected to become severe due to weaker dynamics and a lack of strong instability.
Tonight, the remnants of hurricane Beryl will approach New Brunswick. This system has a track record of being highly convective, with that trend expected to continue as it enters New Brunswick. While mid level instability is currently forecast to be quite minimal, PWAT values are expected to rise up to 50 to 60 mm tonight, so any elevated thunderstorms that develop along the warm front bring the risk of torrential downpours tonight. This risk will continue into tomorrow afternoon over eastern portions of the Maritimes. Strong southerly low level flow tomorrow afternoon over the Bay of Fundy will pump some additional moisture into the warm sector over southern New Brunswick. This will increase the risk for some higher rainfall rates here in any convection that does occur in the warm sector, with 25 to 50 mm per hour possible. This area will move east into parts of mainland Nova Scotia and possibly eastern PEI tomorrow evening. Some isolated thunderstorms are also possible over extreme northwestern New Brunswick early tomorrow evening, closer to the low center, though these are expected to remain non-severe.
Thunderstorm Outlook for Today
Thunderstorm Outlook for Tonight
Thunderstorm Outlook for Tomorrow
Copp