Convective Discussion
Showers at times heavy and isolated thunderstorms are expected today over eastern Nova Scotia, parts of western and southern Newfoundland and over the central and southern marine district today and tonight. An isolated thundershowers is also possible this afternoon over central and western New Brunswick.
Technical Discussion
An upper level trough over the Maritimes will push eastward today towards Newfoundland. There are a couple of surface low pressure areas over the Gulf of St. Lawrence and another over LaHave Bank. Convection has been firing up this morning ahead and near the vicinity of these lows where the air mass remains quite moist and unstable. There is a tropical moisture feed in the southerlies ahead of this trough and some areas of Nova Scotia have already seen heavy downpours (Nappan saw 29mm in one hour) this morning. There is ample low level moisture with precipitable water values near 45mm and dew points between 18-20C, so the concern will continue to be locally heavy downpours with some area exceeding rates of 25mm/hr. Adjusting the 12Z sounding at Stephenville, CAPE values could reach 500 J/kg if they get a bit of solar insolation this afternoon and with shear values in the mid to low 20KT range so there is a low threat for damaging winds.
For areas over central and western New Brunswick, skies are relatively clear this morning and daytime convection may initiate some pop up showers or thundershowers this afternoon. Shear is relatively low so should anything develop they will be slow moving so heavy downpours are possible.
Regional Impacts
Eastern Nova Scotia, eastern PEI and Newfoundland: Heavy showers in TCu at time and thundershowers giving lighnting and frequent downpours.
New Brunswick: Pop up Tcu or CB this afternoon possible which may give heavy downpours.
Marine areas: The southern Maritime marine district may see gusts to 30KT where the SST are warmer.
Roberta McArthur