Convective Discussion
Convective initiation is possible today over portions of the Maritimes. The best chances will again be north of NB (Gaspe region) where a 100kt anti-cyclonic jet should support more robust cells (and to a lesser degree over the Highlands of Maine). The sounding from Caribou modified with T/Td (31,18) show the possibility of CB’s with tops to 280-300, low SSI and BR# suggests single to multiple cells – of the non-severe variety - that could still produce surface wind gusts of 30-40kt.
The strong Bermuda high is providing fairly a stable environment over the rest of NB, NS and PEI, but the water content of the airmass is significant with precipitable water values approaching 50mm. The Yarmouth sounding shows somewhat favourable lapse rates in the mid to upper level. Surface heating alone should provide CAPE in excess of 500 J/kg, however this will likely not be enough to overcome the stable layer between 850-700mb. Other lifting mechanism would be required and it doesn’t look like the weak seabreeze front will be enough. Regardless, a small area of “risk” is introduced over inland areas of NS north of the Atlantic coast.
Dry conditions are expected over northern half of Labrador with Cumulus/strato-cumulus prevailing in the south. Over Newfoundland, a weak frontal trough will maintain variable cloudiness with TCU’s (tops to 160) giving scattered showers over the southern half of the island.
Regional Impacts
PEI, Newfoundland and Labrador : No impacts expected,
Nova Scotia: Slight risk of a thunderstorm for inland areas (west and central). Downpours and gusty winds are the main threat.
New Brunswick : Risk of isolated thunderstorms mostly north of a line from southeastern Maine to Chaleur region. The development, if any, will occur around the middle part of the afternoon. Strong wind gusts is the main threat. Stronger cells are more likely to develop north and West of NB.
Jean-Marc Couturier