Convective Discussion
There are a few areas of interest today that could see convective initiation this afternoon and evening for parts of the Maritimes and Newfoundland. Embedded thundershowers are possible in the heavy band of rain over central and northern New Brunswick, scattered showers and thundershowers are likely to begin in southwestern Nova Scotia as well as southern New Brunswick and track eastward this afternoon. There may also be a risk of a thundershower in interior Newfoundland this afternoon.
Technical Discussion
There is an upper level trough approaching New Brunswick from Quebec as well as a surface trough currently southwest of Georges Bank moving northeastward towards Nova Scotia today.
There is currently an area of heavy showers over central New Brunswick that will be moving slowly northeastward today. Given the sounding for Caribou this morning, there is little shear and CAPE values look to remain below 500 J/kg due to the cloud cover. The main threat with that will be locally heavy rainfall with precipitable water values ranging from 30-40mm. There is the risk for an embedded thundershowers which could enhance the rainfall. Rainfall warnings and special weather statements have already been issued for parts of New Brunswick.
Areas south of the heavy band in New Brunswick as well as Nova Scotia are clearing out of their low level cloud and are expected to reach convective temperatures of 25 to 30C. Altering Yarmouth’s 12Z sounding, CAPE values between 1000-1500 J/kg are possible. With upper level diffluence, sufficient low level moisture and moderate 0-6km shear, the environment is condusive for single to multicell thundershowers to develop this afternoon and continue into the evening. For Nova Scotia, the trigger may be a mix of surface heating, sea breeze convergence and the influence of the approaching surface trough. Should cells initiate, they will likely begin early this afternoon in the southwest and track east-northeast. There could be heavy downpours, strong wind gusts that could reach 40kts and the possibility of small hail (<2cm).
For Newfoundland there is the slight risk of a thundershower this afternoon with some areas reaching convective temperatures and a weak LLJ over the area.
Regional Impacts
New Brunswick : Risk of an embedded thunderstorm within the area of heavy showers this afternoon. Stronger cell are more likely over Gaspe and southern Quebec but may approach western parts of Edmundston County. For areas south of the heavy showers, isolated to scattered thundershowers are possible giving heavy downpours and strong wind gusts.
Nova Scotia: Isolated to scattered thundershowers are possible starting this afternoon giving heavy downpours and strong wind gusts.
PEI: Showers and risk of thundershowers early this evening and overnight with heavy downpours possible.
Newfoudland: Mainly TCUs with the slight risk of a thundershower this afternoon.
Labrador: nil
Roberta McArthur