Regional Impacts
Today
LAB: Chance of scattered thunderstorms across eastern Labrador this afternoon with small hail, strong wind gusts, and locally heavy downpours.
NL: Chance of an elevated thundershower over the Avalon today with locally heavy downpours.
NS/NB/PEI: None.
Tonight
NS: Slight risk of an isolated thundershower overnight over northern Cape Breton.
NB/PEI/NL/LAB: None.
Tomorrow
LAB: Chance of scattered thundershowers across central and eastern Labrador tomorrow with gusty winds and locally heavy downpours.
NL: Slight risk of an isolated thundershower over central Newfoundland in the afternoon.
NS/NB/PEI: None.
Convective Discussion…
This morning, an upper low sits over northern Quebec with two troughs extending south. The first trough reaches from the Labrador Sea down into the Avalon Peninsula, then south into the Atlantic. Some lightning activity was observed in this trough overnight as it moved east across Newfoundland. The risk for an elevated thundershower continues early this afternoon for the Avalon, but the trough will slowly move east out of the region by this evening. A few brief heavy downpours will be possible in these thundershowers due to some high precipitable water over the area, with 41 mm observed on the 12Z St. John’s sounding this morning. Storms aren’t expected to become too organized here today however, due to a lack of instability in the weakening trough, but some marginally severe rainfall rates are possible due to the high precipitable water. Elsewhere, the second trough is slowly moving east and extends from the upper low through central Labrador, and down into the Gulf of Maine. Some thunderstorms are expected to trigger along this trough later this afternoon over eastern Labrador, where MLCAPE is forecast to rise near 750 J/kg in addition to a diverging 500 mb jet approaching from the southwest this morning. Some storms may become organized due to effective shear of 30 to 40 kts, but none are expected to reach severe criteria. PWATs over the area are forecast to be around 20 to 25 mm, so rainfall is not a primary concern. DCAPE close to 700 J/kg however could produce some strong wind gusts in the more organized cells.
Tonight, the second trough in question will continue to move east, extending down into the Gulf of St. Lawrence. A 250 mb jet will approach from the west, to lie over the surface trough overnight, which could spark up a brief thundershower or two. These cells could impact parts of PEI and northern Cape Breton overnight and into early tomorrow morning, but the risk remains low at this time. By tomorrow afternoon, both the jet and the trough will sit over central Newfoundland. MLCAPE is expected to remain near 500 J/kg here tomorrow, with the models showing some cloud cover lingering into the late morning. If this cloud is able to clear out a bit quicker than forecast, instability may be able to rise a bit higher but confidence is low at this time. Nonetheless, the risk does exist for an isolated thundershower or two over central Newfoundland tomorrow afternoon which could produce brief heavy downpours and some gusty winds. There is also the risk of some scattered thundershowers over central and eastern Labrador tomorrow afternoon around the upper low as it spins out over the Labrador Sea. Instability is expected to be lower here though, 250 to 500 J/kg MLCAPE, so the risk remains fairly low.
Thunderstorm Outlook for Today
Thunderstorm Outlook for Tonight
Thunderstorm Outlook for Tomorrow
Forecaster: Copp