Regional Impacts
Today
LAB: Scattered thunderstorms possible today capable of producing small hail, strong wind gusts, and heavy downpours.
NS/Newfoundland: Chance for some elevated thundershowers today over Cape Breton and southern Newfoundland with some locally heavy downpours.
PEI/NB: None.
Tonight
LAB: Some isolated thundershowers possible overnight over northern and western Labrador.
NS/NB/PEI/Newfoundland: None.
Tomorrow
NB: Chance of some isolated thunderstorms over northwestern New Brunswick in the afternoon and evening with small hail, strong wind gusts, and locally heavy downpours.
LAB: Some scattered thundershowers possible through the day over central Labrador capable of producing some locally heavy downpours.
NS/PEI/Newfoundland: None.
Convective Discussion…
Two areas of interest are in play today. The first is associated with an upper low between Cape Breton and southern Newfoundland, and the second associated with an elongated trough extending from the northern Labrador Sea down into southern Quebec. Some isolated thundershowers have already been observed this morning with this first feature along the Eastern Shore of Nova Scotia. The upper low will slowly move northeast, reaching the Avalon Peninsula overnight. Due to the amount of cloud cover over this area of interest, convection is expected to remain elevated through the day as some scattered thundershowers move into southern Newfoundland. MUCAPE values of 250 to 500 J/kg are forecast, with effective shear in the 15 to 25 knot range allowing some of these thundershowers to be sustained through the day. The main risk with these cells will be heavy rainfall rates of 20 to 30 mm per hour. This low will move east over the Atlantic tonight. The second feature over Quebec and Labrador has already produced some scattered thunderstorms, which are expected to continue through the day and into this evening. MLCAPE is expected to build near or above 1000 J/kg by early this afternoon over western Labrador, in addition to some moderate jet support providing effective shear in the range of 20 to 30 knots by late this afternoon. This should allow some cells to become organized this afternoon and into this evening, with the main hazards being some heavy downpours, strong wind gusts, and small hail. This trough is moving very slowly to the northeast which could ramp up some of the rainfall totals over the area. This risk will extend overnight and into tomorrow, but without daytime heating only a few isolated non-severe thundershowers are expected overnight.
Tomorrow, the same trough will likely spark some non-severe thundershowers over central Labrador, with MLCAPE expected to be much lower (250 to 500 J/kg) due to enhanced cloud cover over the region. However, the environment over northwestern New Brunswick is expected to ramp up by the mid-afternoon as the trough moves into the St. Lawrence river valley. Clear skies during the morning and early afternoon here should allow MUCAPE values to build to 750 to 1000 J/kg. This in combination with effective shear values of 20 to 30 knots could lead to some organized thunderstorm development in the mid-afternoon over northwestern New Brunswick. However current model tephigrams indicate a layer of warm air above 500 mb which could keep storms from reaching severe status. The timing of the trough will also play a role in when convection triggers, so there is still some uncertainty here tomorrow. The main hazards with any storms that do fire will be small hail, strong wind gusts, and locally heavy downpours.
Thunderstorm Outlook for Today
Thunderstorm Outlook for Tonight
Thunderstorm Outlook for Tomorrow
Forecaster: Copp