Convective discussion:
Possible severe thunderstorms for Monday afternoon into the evening, with a slight chance for supercells for New Brunswick.
Technical Discussion:
A low pressure system west of James Bay will move to lie over Ungava Bay Tuesday night.
For New Brunswick the warm front should pass north of the province tonight, but then there will be increasing low level moisture and warm advection in the warm sector, along with increasing shear as the cold front from the low approaches. Current model tephis show an almost classic shotgun setup, with the inversion breaking between 18-21Z. Currently CAPES are forecast in excess of 1000 J/kg, precipitable water 30-40 mm. The shear start a bit light at 25 kts, but increases into the evening to 35 kts. Finally Storm Relative Helicity is in the 150-250 m^2/s^2.
On the other hand the steering flow will be west to west-southwest, so it could skim by to the north, and the trailing front will also be mainly in the north. Also, the Bulk Richardson Number indicates CAPE dominating shear, so it may be more of a multicell scenario than supercells, and in fact the guidance is hinting at a prefrontal line.
For Labrador the warm front will pass through western Labrador by noon, quickly followed by the cold front. In the west, if the system passes a little farther north, there may be some convection with heavy rainfall.
Regional Impacts:
New Brunswick: heavy downpours, gusty winds, maybe small hail, and maybe a supercell. Wind will be an issue if a prefrontal squall line forms.
Labrador: Possibly heavy downpours.
Nova Scotia/Prince Edward Island/Newfoundland/Iles de la Madeleine: nothing significant.
Doug Mercer