Convective Outlook Valid for Today , Tonight and Tomorrow

Regional Impacts

Nova Scotia.. Slight Risk of thunderstorms today giving heavy downpours and strong winds.

New Brunswick.. Slight Risk of thunderstorms today giving heavy downpours and strong winds. Risk of Severe thunderstorms late tomorrow.

PEI… Low risk of thunderstorms.

Newfoundland.. Slight Risk of thunderstorms today giving heavy downpours and strong winds.

Labrador.. Slight Risk of thunderstorms today giving heavy downpours and strong winds.

Convective Discussion

Our generally unsettled air mass will remain unstable today, with CAPE values exceeding 1000 J/kg across much of the Atlantic Provinces. Moderate shear could be a factor in the Maritimes, with a slight chance that some thunderstorms become organized and possibly back-build.

Over Newfoundland, beneath the upper trough, storms are likely to remain fairly stationary, with little shear available for organization. One possible concern is the development of thunderstorms across northern regions, with new storms forming along a potential land-sea boundary. However, under these very low-shear conditions, it is challenging to determine where storm activity will become most dominant. Torrential downpours and strong wind gusts will be possible with these storms.

Tomorrow, we will see the return of much stronger dynamics as the upper-level jet and stronger shear come into play. The biggest issue will be the timing of cap erosion. Should strong cells move into northwestern New Brunswick tomorrow afternoon—likely later in the day—there is a good chance these storms will exhibit significant mid-level rotation. Damaging winds and even tornadic storms cannot be ruled out.

There remains some uncertainty, but Canada Day has the potential to be problematic from late tomorrow into the evening, especially across northwestern New Brunswick.

Thunderstorm Outlook for Today

Thunderstorm Outlook for Tonight

Thunderstorm Outlook for Tomorrow

 

Mel Lemmon

Convective Outlook Valid for Today, Tonight and Tomorrow

Regional Impacts

Today

LAB: Chance of some scattered thundershowers, some may be capable of producing small hail, strong winds, and locally heavy downpours.

NFLD: Chance of scattered thundershowers in the afternoon capable of producing some strong wind gusts, small hail and locally heavy downpours.

NB: Risk of isolated thunderstorms in the afternoon and early evening which may produce strong wind gusts, small hail, and heavy downpours.

NS/PEI: Risk of an isolated thundershower this afternoon in western PEI and Cape Breton.

Tonight

LAB: Some lingering thunderstorms are possible across southeastern Labrador.

Tomorrow

NS/NL:  Risk of scattered thunderstorms in the afternoon and early evening which may produce strong wind gusts, small hail, and heavy downpours.

NB/LAB: Risk of isolated thunderstorms which may produce brief strong wind gusts, small hail and heavy downpours.

Convective Discussion

The environment remains unstable today across much of the Atlantic Provinces as a cold upper trough stretches from Labrador southwestward towards the northern Gulf of St. Lawrence and northern New Brunswick today. Along and east of the trough axis, mainly sunny skies should allow for good daytime heating into this afternoon. One hinderance may be some smoke aloft which is drifting across southern Labrador and into the Gulf from fires in central Quebec. Regardless, with the potential for MLCAPE to reach or exceed 1500J/kg, and increasing effective shear of 20 to 30 kts, as well as low freezing levels, some storms that develop may reach near severe limits. Multicell storms are most likely with small hail, strong wind gusts and heavy downpours possible, especially as storms will not be moving quickly and may train over the same areas. Enhanced lift due to terrain and sea breeze convergence will aid in some pop-up convection developing across central Newfoundland this afternoon. Shear is lower over this area, so heavy downpours and small hail are the main threat with anything that develops. A weak shortwave trough is expected to reach northern New Brunswick and into the Gulf of St. Lawrence but not until later tonight, likely limiting any severe convection to the Gaspe Peninsula, but an isolated risk is possible with this overnight. This upper trough has a history also of cold core funnels which were witnessed in PEI yesterday, and similar conditions may also occur today.

For tomorrow, the troughing continues southeastward with isolated showers across most areas by the afternoon, but the higher threat of thunderstorms shifts to Newfoundland and central to eastern Nova Scotia where precipitable water is increasing. Surface convergence and daytime heating will aid in increasing instability. There is a risk of multicell or a possible isolated supercell along convergence lines in the late afternoon or evening. Over Labrador, the upper forcing diminishes but daytime heating and terrain influences may still allow for pop-up convection in the afternoon but with quite low dew points, brief strong wind gusts are the main threat.

Thunderstorm Outlook for Today

Thunderstorm Outlook for Tonight

Thunderstorm Outlook for Tomorrow

 

Convective Outlook Valid for Today, Tonight and Tomorrow

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

Convective Outlook Valid for Today , Tonight and Tomorrow

Regional Impacts

 

Today

NS/NB/LAB: Chance of scattered thundershowers.

PEI/NFLD: None.

 

Tonight

NB: Chance of elevated thundershowers.

NS/PEI/NFLD/LAB: None.

 

Sunday

NB/LAB: Chance of organized thundershowers central and west.

NS/NFLD: Chance of scattered thundershowers.

PEI: None.

 

Convective Discussion

Scattered thundershowers are possible across Nova Scotia, New Brunswick and extreme southeast Labrador today. CAPE values of 500 J/kg and shear near 20 knots will limited any thundershowers to non-severe. Downpours with training are the most likely event today with PWAT values near 30 mm and winds remaining light. On Sunday, the environment remains quite similar with scattered thundershowers once again possible across most of the region however over New Brunswick and southeast Labrador CAPE values will increase to near 1500 J/kg while shear will remain near 20 knots. This may produce gusty wind and downpours for those regions. Hopefully the lack of shear will keep conditions below warning criteria.

 

Thunderstorm Outlook for Today

Thunderstorm Outlook for Tonight

Thunderstorm Outlook for Tomorrow

Convective Outlook Valid for Today, Tonight and Tomorrow

Regional Impacts

Today

NB/NS/PEI: Risk of showers and thunderstorms across NB in the afternoon into western NS and PEI in the late afternoon/evening giving brief wind gusts and heavy downpours. There is a chance that a cell or two could approach severe limits late this afternoon near Keji National Park and in the Annapolis Valley of Nova Scotia. This convection should be short lived based on the dynamics today. The main hazard is rain.

Labrador: Scattered thunderstorms across the region from early afternoon to the evening giving brief wind gusts, lightning, and small/moderate hail.

NL: None

Tonight

NS: Chance of thunderstorms continues after midnight across eastern sections and over much of the marine district.

Tomorrow

NB/NS/PEI: An inland risk for single cell convection exists tomorrow across much of the Maritimes.

Labrador: The thunderstorm risk has pushed east near Mary’s Harbour, depicted in grey.

NL: Inland thundershowers are possible near Badger, depicted in grey.

Convective Discussion

A tale of 2 trofs today across the Maritimes. As these features advance from the Eastern Townships of Quebec, the atmosphere will destabilize. A jet at 250 of 112kts also sweeps through western NS late this afternoon, coinciding with the advancing thermal trof. This alignment MAY lead to a cell or two approaching severe limits in the small depicted yellow risk area. Dewpoints this morning hover around 12-15 and should maintain today along the warm frontal feature (sfc). The main hazard this afternoon would be rainfall, but also a brief wind gust to near 90km/h. CAPE is limiting however, and a lot of cloud already around – increasing CIN. MUCAPE values only near 500 today. Decaying storms may brush the HRM area late this evening, but not with any of their severe hazards maintained. CAPE is much higher with Eff shear of 30kts in Labrador. Hence the hail risk and more organized chance of discrete cells forming there. Tomorrows convection is forecast to be single cell and not severe. These will be inland airmass thundershowers, very typical to the region in June.

Thunderstorm Outlook for Today

Thunderstorm Outlook for Tonight

Thunderstorm Outlook for Tomorrow

Forecaster: Tirone.