Regional Impacts
Today
NB: Risk of severe thunderstorms over parts of western and central NB today, capable of producing small hail, strong wind gusts, and torrential downpours.
NS/LAB: Chance of some scattered thundershowers this afternoon capable of producing strong wind gusts and locally heavy downpours.
NFLD: Chance of some isolated thundershowers this afternoon which may produce some locally heavy downpours.
PEI: None.
Tonight
NS/NB/PEI/NFLD/LAB : None.
Tomorrow
NB: Risk of isolated thunderstorms over northern NB in the afternoon which may produce strong wind gusts, small hail, and heavy downpours.
LAB: Chance of some scattered thundershowers in the afternoon, some may be capable of producing small hail, strong winds, and locally heavy downpours over southeastern Labrador.
NFLD: Chance of some isolated thundershowers in the afternoon capable of producing some strong wind gusts and locally heavy downpours.
NS/PEI: None.
Convective Discussion…
An active day has already set up over parts of New Brunswick today and severe thunderstorm watches have been issued. Some thundershowers moved into western New Brunswick early this morning associated with a small shortwave and have already produced some marginally severe rainfall rates. Some brief clearing is expected over western and central New Brunswick early this afternoon which will allow MLCAPE values to rise up to 1000 – 1250 J/kg, providing more than enough instability for storms to continue firing into this evening. Wind shear remains a slight uncertainty however, with effective shear values varying from 10 knots in the northern half of the province to 20 to 30 knots in the southern half. The storms in the northern half of New Brunswick this afternoon are expected to be very slow-moving and short-lived due to the lack of shear, but these storms are still likely to produce some torrential rainfall rates. This risk also exists in the south, but due to the higher shear, more of a multicellular storm mode is expected which could lead to some training thunderstorms. The main hazard in New Brunswick today is the potential for significant rainfall, but small hail and strong wind gusts are also possible.
Elsewhere, a few pop-up thundershowers are possible over Newfoundland and Nova Scotia this afternoon. Although effective shear over Nova Scotia is similar to southern New Brunswick today (20 to 30 kts), limited MLCAPE of 500 to 750 J/kg should keep these storms sub-severe but will still be capable of producing some strong wind gusts and heavy downpours. Shear is much less over Newfoundland, so any storms that fire here this afternoon will likely be short-lived. Parts of southeastern Labrador could see the potential for some marginally severe storms this afternoon associated with a weak surface trough and some weak vorticity advection at 500 mb. MLCAPE and effective shear is forecast to be marginally higher here than in Nova Scotia/Newfoundland, 1000 J/kg and 20 to 30 knots respectively. This could lead to the potential for some strong wind gusts and locally heavy downpours in any storms that fire here today. One of the major limiting factors however are very low dewpoints. Current observations show surface temperatures in the area in the low to mid twenties, with dewpoints of only around 4 to 8 degrees. This will likely lead to storms being very high based, making it difficult for the aforementioned hazards to reach the ground.
Tomorrow, a similar setup is expected across Newfoundland and Labrador but with slightly better shear across the region due to an approaching upper trough. In New Brunswick, effective shear of 25 to 30 knots and slightly higher MLCAPE than today (1250-1500 J/kg) is expected. There remains some uncertainty in New Brunswick however due to the timing of the shortwave moving in, as well as how much mid and low-level moisture will be available. Current guidance indicates that the shortwave won’t reach northern New Brunswick until late evening which keeps the risk of storms initiating fairly low, but the afternoon environment is supportive of some marginally severe hazards if storms do end up developing.
Thunderstorm Outlook for Today
Thunderstorm Outlook for Tonight
Thunderstorm Outlook for Tomorrow
Forecaster: Copp