Convective discussion:
Scattered thunderstorms associated with an upper level short over the Maritimes will move over WRN NL and SE LAB this afternoon and evening. Isolated thundershowers over parts of CNTRL/WRN LAB in the vicinity of an upper low will become more widespread this afternoon. Scattered thunderstorms will develop over ERN NB, ERN and NRN NS, PEI and Cape Breton this afternoon.
Technical Discussion:
A short wave trough and associated PVA triggered some early morning thunderstorms across CNTRL/NERN NB, and this area will move into WRN NL and SE LAB this afternoon. Upper air analysis shows a strong 250 mb jet axis (around 100 knots) and also a strong 500 mb jet (around 55 knots) with decent divergence. This area will not necessarily need lift from the surface, so cloud cover shouldn’t inhibit convection. There is an upper trough at 500/700 mb progressing slowly eastward, so falling heights and clearing skies should trigger some cells over portions of the MRTMS this afternoon. In addition a surface trough/cold front (analyzed at 12Z to be crossing NB) should aid in thunderstorm development. There is ample moisture near the surface, but the question is how quickly the surface dewpoints drop. 12Z tephi analysis shows good shear across the region (35-45 knots) but the instability is not as impressive as yesterday. In addition, adjusting the profiles for a Tmax of 26-27 produces about 500-700 CAPE, so the Buoyancy will not be that great either. Some storms could produce gusts to 40 knots with torrential downpours (precipitable water is 30-40 mm). Hail will not be a concern given the low buoyancy and associated weaker updrafts in cells. That being said small hail is possible within the stronger storms. Severe weather is not anticipated, however a very isolated severe cell in ERN NB, ERN/NRN NS and PEI cannot be ruled out.
Regional Impacts:
New Brunswick: Scattered non-severe thunderstorms across the east this afternoon. Slight risk further to the west.
Prince Edward Island: Scattered non-severe thunderstorms this afternoon.
Newfoundland: Scattered afternoon/evening thunderstorms in the west. Slight risk in the east.
Labrador: Scattered non-severe thunderstorms.
Nova Scotia: Scattered non-severe thunderstorms this afternoon in the north and east (as well as Cape Breton).
Jeremy