Regional Impacts
Labrador: some isolated thundershowers expected today associated with a southeastward moving trough of low pressure. Gusts to 70 km/h are possible.
Central/eastern/northeastern Newfoundland: a slight chance of late afternoon and evening thundershowers.
Maritimes: a chance of thundershowers today and tonight in association with a fairly stationary upper level low.
Convective Discussion
Labrador:
There is a fairly strong 700-500 mb jet descending from Ungava Bay area (YVP has about 55 knots of shear based on the 12Z tephi). A surface frontal zone could trigger some isolated cells this afternoon and into this evening as daytime highs hit the upper 20’s to low 30’s. PWAT at YVP is close to 40, but the air mass is moving into a drier zone, so heavy downpours shouldn’t be an issue at this time. Given the dryness below 700 mb at YYR, some wind gusts in cells is a possibility. Right now gusts to 70 seem reasonable.
Central/eastern/northeastern Newfoundland:
There is a weak area of instability laying across the aforementioned areas on the island. Given the latest sat pix skies appear to be clearing so there is a risk of isolated cells this afternoon and into this evening. 12Z YJT tephi is not particularly interesting, but with enough solar insolation CAPE could reach 300. Given about 15 knots of 0-6 km shear, weak pulse cells are expected.
Maritimes:
Lastly, the stubborn upper area of low pressure west of the MRTMS. Yesterday the guidance was suggesting potential for some heavy downpours given PWAT was above 40mm and in an area of modest divergence aloft, but there was next to nothing. Lots of activity over the marine areas, but nothing at all over land. So given the history of the upper low only a slight risk of a TSRA is expected, and this would mainly apply to Nova Scotia tonight. Not included in the risk zone is northwestern New Brunswick. If given enough surface heating an isolated cell is possible. Right now I am expected mostly TCUs.
Thunderstorm Outlook for Day 1
Convective Discussion
The greyed area is a combination of the leftover upper low that will be weakening somewhat and the approaching frontal trough over Labrador. With the increasing shear associated with the trough some gusts to 70 km/h are possible over southern Labrador (of course where only the caribou roam).
Thunderstorm Outlook for Day 2
Jeremy