Convective Discussion
Convection is occurring ahead of a cold frontal trough stretching from central Labrador south through eastern Nova Scotia toward the southern marine district. The trough will continue to push slowly eastward today to lie over Newfoundland by early tomorrow morning. Rainfall rates have been the primary concern with this front as it brought close to 50 mm over central New Brunswick yesterday and this morning a heavy band of rain and embedded thundershowers moved over mainland Nova Scotia giving total rainfall amounts greater than 40 mm. Once the band moves off of Nova Scotia early this afternoon, it is expected that the heaviest rainfall rates will now remain over the southern marine districts but may reach portions of southern Newfoundland.
Technical Discussion
Over central Labrador and Newfoundland: The dynamics near the low and along the cold front have weakened overnight. There is a strong 250mb jet but is not well aligned to help enhance any convection. However with cooling heights aloft there is still the risk for non severe thundershowers this afternoon as the front continues to approach Newfoundland. The highest rainfall is forecasted to remain over the marine district but there may still be some high rainfall rates that make it into southern Newfoundland today and overnight. Precipitable water values near 40 mm have already streamed northward toward YJT.
For eastern Nova Scotia and the southern marine districts: Heavy showers with embedded thundershowers will continue to push into Cape Breton in the next hour. The heaviest showers are aided by a 30KT LLJ over eastern NS extending northward towards Port Aux Basques. There is a weak low pressure area developing in the trough southwest of Georges Bank and is forecast to move northeastward into the southern slope waters late this evening. There is already frequent lightning near and ahead of the low as it lies still within the warmer gulf stream waters. That activity may continue into the southern slope waters this afternoon and overnight where SSTs continue to be warm. Gusts to 35 KTS are possible over the southern slope waters of Georges Bank and West Scotian Slope The convection will likely become more isolated as it approaches our cooler waters further north an low level stability increases, however cloud top cooling may provide enough upper level energy to keep convection going overnight. Over the southeastern Grand Banks toward East Coast, there is a bit of upper level instability this morning firing up a few thundershowers but they are not expected to be severe and should diminish during the day.
Regional Impacts
For eastern Nova Scotia and the southern marine waters
Lightning, heavy downpours and gusts are possible.
For Newfoundland
Lightning and heavy downpours for the south coast.
For Labrador
Lightning and brief gusts for central and eastern Labrador.
Roberta McArthur