Regional Impacts
Today
NS/PEI/NB: Chance for some scattered thundershowers today across mainland Nova Scotia, eastern PEI, and southeastern New Brunswick with some gusty winds and locally heavy downpours.
LAB: Chance of an isolated thundershower along the Labrador coast this afternoon.
NL: None.
Tonight
NS/PEI/NL: Chance for some elevated thundershowers overnight.
NB/LAB: None.
Tomorrow
NB/LAB: Risk of scattered thunderstorms over northwestern New Brunswick and western Labrador late in the day tomorrow with small hail, gusty winds, and heavy downpours.
NL: Chance of an isolated thundershower over western Newfoundland through the day with locally heavy downpours.
NS/PEI: None.
Convective Discussion…
This morning, a weakening upper low sits over central Labrador, with an elongated trough extending south from the Labrador Sea into the Maritimes, where a weak surface low sits off the southwest coast of Nova Scotia. This surface low will be the main driver for convection today, with a few lightning strikes already observed offshore. Current model guidance already has some clearing over southeast New Brunswick and PEI, leading to forecast MLCAPE values of 750 to 1000 J/kg over this area, but persistent low level cloud cover over most of the Maritimes has held on this morning and the longer it sticks around, the less likely MLCAPE values are to build over 500 J/kg. Thus, most of the convection is likely to occur around the low center (where the best MUCAPE is available) as it slowly moves northeast through the day. Weak effective shear (~20 kts) is likely to keep storms from becoming organized, but due to the slow moving nature of the trough, as well as high PWATs (44.6 mm on 12Z Yarmouth sounding), some slow moving cells could drop some near-severe rainfall rates of up to 20 mm per hour over mainland Nova Scotia. Elsewhere, the upper low in Labrador could spin up some isolated thundershowers this afternoon. A bit more clearing is evident here which should allow some instability to build ahead of the upper low. Once again though, a lack of effective shear (15 to 25 kts) and some weak lapse rates will likely keep anything from becoming organized, but a few lightning strikes are possible.
Tonight, the surface low south of Nova Scotia will continue to move northeast to lie near PEI by late tomorrow morning. A slight chance of some elevated thundershowers are possible to the north and east of the low as some better jet support moves in from the West tonight. By tomorrow afternoon, the low will be approaching Newfoundland, which brings the risk for some elevated thundershowers to the western half of the island and southern Labrador. Weak lapse rates however keep the risk quite low but with similar PWAT to Nova Scotia today, some heavy downpours of 10 to 20 mm per hour are possible in any storms that do fire.
Late in the day tomorrow, a trough will approach from Quebec, bringing the risk for some scattered thunderstorms over northwestern New Brunswick and western Labrador. There is a lot of uncertainty with regards to initiation here, the first being the timing of the trough which is currently forecast to enter New Brunswick tomorrow evening. A large CAP is also evident between 700 and 500 mb which will likely keep storms from firing tomorrow afternoon ahead of the trough. Cloud cover could also pose an issue for convective initiation, with some hi-res guidance hinting at low level cloud lingering into the afternoon over most of New Brunswick. This would drastically limit MLCAPE from building during the day, severely limiting the environment storms can fire in. Given enough clearing tomorrow and if the trough moves through early enough, the risk does exist for some small hail, strong wind gusts, and locally heavy downpours across northern New Brunswick and western Labrador.
Thunderstorm Outlook for Today
Thunderstorm Outlook for Tonight
Thunderstorm Outlook for Tomorrow
Forecaster: Copp