Convective Discussion
Garden variety thundershowers possible for New Brunswick, and significant wind gusts and rainfalls for Northeastern Newfoundland.
Technical Discussion
The main risk is for Newfoundland, especially the northwest. Low level moisture is moving in with the west/southwesterlies, there will be good insolation as the cells move east, and there’s some PVA ahead of a trough approaching from the Gulf of St. Lawrence. Also, dewpoints at 12Z were in the 16-17 C range, especially for Cantral and eastern areas. Precipitable water is in the 30-40 range from the 12Z soundings, and shear is about 40 kts. CAPE could be up to 500 J/kg, and possibly larger if daytime heating is higher than forecast. With dry midlayers and a fairly classic daytime heating tephi profile, healthy downdrafts are likely, followed by good local downpours. With freezing levels between 110-130 hft, hail is unlikely, especially combined with the relatively low CAPE. Onset should be early to mid afternoon.
For New Brunswick: For this case precipitable water is about 25, the freezing levels are too high for significant hail, and while low levels will become unstable there is an inversion near 14,000 feet that probably will inhibit significant convection. Guidance hints at the inversion gradually eroding away and allowing some convection to occur. If so, they will be classic popcorn, with some downdrafts and locally heavy showers. Preipitable water is near 24 mm, and shear is near 30 kts. For Nova Scotia there is a bare chance of an isolated thundershower or two.
Regional Impacts
Labrador: none.
Newfoundland: Thunderstorms over much of the interior, with the northeast having a risk for strong and gusty winds, followed by local heavy downpours. Significant hail is unlikely.
New Brunswick: isolated shallow based cells capped near midlevels.
Nova Scotia: Isolated cells east.
Prince Edward Island: none.
Doug Mercer