Regional Impacts
NS/NB/PEI… Scattered thunderstorms possible across the central Maritimes this afternoon, main risks are heavy downpours, strong wind gusts, and small hail.
NLFD… Isolated thunderstorms possible in central Newfoundland this afternoon, main risks are strong wind gusts and heavy downpours.
Convective Discussion…
As very warm temperatures continue across the Maritimes today, a cold front will begin to move south across the region. Surface based CAPE values are forecast to soar upwards of 2000 J/kg in southern New Brunswick and mainland Nova Scotia ahead of the front in addition to decent bulk shear values of 30 to 35 kts. Due to the strength of the ridge south of Nova Scotia, the front is expected to slow down and weaken as it moves across New Brunswick, and stall over southern Nova Scotia tonight. This will cause some issues in the erosion of the thermal ridge, especially over southern Nova Scotia. In addition, the location of the 500 mb jet over central Quebec is not ideal. As such, the main focus for severe thunderstorms will be in southeastern New Brunswick and central Nova Scotia today. PWAT values on the Yarmouth tephigram this morning indicate 45 to 50 mm, which is consistent with what models have been forecasting ahead of the front. With these high PWAT values, heavy downpours of 25 to 50 mm/h are expected to be the main hazard with any thunderstorms that develop, in addition to strong wind gusts of 70 to 90 km/h and small hail up to dime size.
A second round of convection may move through southern Nova Scotia from the west overnight tonight, as a weak shortwave rides the thermal ridge across the region. Heavy downpours may company these storms if they persist over the Gulf of Maine.
In central Newfoundland, similar conditions to central Nova Scotia are expected, however bulk shear values are likely to be slightly lower here (20 to 25 kts), which may prevent more organized thunderstorm activity. Another limiting factor is a layer of warmer air evident in the mid levels persisting over central Newfoundland today. Any thunderstorms that do develop may struggle to get organized, but may produce strong wind gusts of 70 to 90 km/h and heavy downpours up to 25 mm/h, in addition to the small chance of some pea sized hail.
Thunderstorm Outlook for Today
Thunderstorm Outlook for Tonight
Thunderstorm Outlook for Tomorrow
Copp