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.

Convective Outlook Valid for Today, Tonight and Tomorrow

Regional Impacts

Today

NB: Some isolated thunderstorms are possible over western regions giving brief winds, heavy downpours and small hail.

Labrador: Some isolated thunderstorms are expected for western regions giving brief winds gusts and small hail.

NS/PEI/NL: None

Tonight

None.

Tomorrow

NB/NS/PEI: Risk of thunderstorms across NB in the afternoon into western NS and PEI in the evening giving brief wind gusts and heavy downpours.

Labrador : Scattered thunderstorms across central and southern regions from early afternoon to the evening giving brief wind gusts and small hail.

NL: None

Convective Discussion

As a low pressure system pulls east of Newfoundland this morning, weak ridging build across the eastern Maritimes, Newfoundland and southeastern Labrador today, limiting convection. To the west, a trough of low pressure will slowly advance southeastward from northern Quebec, with another trough of low pressure  across the Great Lakes. Two areas to watch today will be ahead of these two features as they enter western Labrador and western New Brunswick this afternoon. With MLCAPE of 500 J/kg and effective shear of 15-20kt, convection that develops is not expected to be that organized, but could still give be some brief wind gusts and small hail into western Labrador given low freezing levels. For the environment entering western New Brunswick, there is similar CAPE values but a bit more shear of near 35-30kt and precipitable water of near 25 mm, which could lead to some organization across southwestern areas this afternoon. Multicell or possible lines may develop and brief strong wind gusts and small hail are possible, although upper support remains further west today, so are not expected to reach severe limits.

For tomorrow, the ridge holds over Newfoundland, but the two troughs continue further east, with the northern trough over central Labrador and the southern trough across southern Quebec and into northern Maine by the evening. More widespread showers and thundershowers are expected for Labrador with some organization possible into multicell or lines as MLCAPE increased to 1000J/kg and effective shear increasing to near 30 kt. Small hail and strong wind gusts will be the main threats given it will be quite dry in the low levels. For the Maritimes, the trough advances towards Maine with some potential for more organized thunderstorms given increasing shear, but CAPE remains near 500J/kg. There is increasing precipitable water of 35 mm, leading to higher rainfall rates in embedded convection in the evening across southern New Brunswick and western Nova Scotia.

Thunderstorm Outlook for Today

Thunderstorm Outlook for Tonight

Thunderstorm Outlook for Tomorrow

Forecaster: McArthur

Convective Outlook Valid for Today, Tonight and Tomorrow

Regional Impacts

Today

NB: Thunderstorms are forecast to develop this afternoon and early evening. Severe storms are possible along and south of Highway 2, with gusty winds and moderate hail. (Depicted in yellow).

PE/NS: Some of these storms may survive across the Strait and Bay entering PEI/NS this evening in their late stages of development. They won’t be building any further at this point. (Depicted in grey)

Cape Breton/Avalon/Burin: Embedded -TS risk near noon and this afternoon along the Atlantic coast and offshore. Heavy rain occurring in areas, but no other hazards forecast.

Tonight

Atlantic: No thunderstorms forecast in the overnight time period.

Tomorrow

Western Labrador: Thunderstorms are forecast to re-develop in the afternoon and evening hours. Some may approach marginal severe limits.

NB: Western and northern areas of the province could see a few lightning strikes as thunderstorms re-develop in the afternoon. Not forecast as severe at this time.

Friday

NS: Western NS and the Annapolis Valley could see organized convection that approaches severe limits. This will be analyzed further in coming shifts.

 

Convective Discussion

There is ample moisture again today across the Maritimes. LL cloud/fog is expected to burn back in NB late this morning, setting the stage. Today, a forcing at the 500mb level is at play. This thermal trof is expected to sweep through NB this afternoon, and brings the chance of all hazards to areas in the province (depicted in yellow). MLCAPE sits near 1800J with Effective shear values 30-40kts. Watches will likely be issued in the area of Woodstock and Fredericton. Dewpoints across NS are also near 15 this AM, but there is a lack of a sfc forcing as the synoptic rain effects most of the central and eastern region at present. If a discrete line of storms is able to form in SW-SE NB, the biggest hazard is the wind threat. Gusts could be over 90km/h in an organized complex – storm motion to the ESE. These cells also may survive across the Northumberland Strait and Bay of Fundy with a strong 700 steering flow late day today. The grey hazard area is extended to reflect this evening risk. It should also be noted that helicity today is non-zero. This, along with low freezing levels, will be monitored closely.

Thunderstorm Outlook for Today

Thunderstorm Outlook for Tonight

Thunderstorm Outlook for Tomorrow

Forecaster: Tirone.

Convective Outlook Valid for Today, Tonight and Tomorrow

Regional Impacts

Today

NB: Chance of some scattered embedded thundershowers over southern New Brunswick this afternoon and evening with some locally heavy downpours.

Lab: Chance of scattered/frequent thunderstorms through southern Labrador today. These could be marginally severe with gusty winds and heavy downpours (locally).

NS: Scattered embedded thundershowers over most of mainland NS this afternoon and evening. Rain is the biggest hazard.

Tonight

NS: Thunderstorms continue over eastern sections as well as much of the marine district.

Tomorrow

NB: Thunderstorms are forecast to develop late afternoon and early evening. Severe storms are possible along and south of Highway 2, with gusty winds and moderate hail.

 

Convective Discussion

Labrador has lit up quite quickly today with lightning across the southern tier. These storms (spawning from a low centre anchored way back to the west) have a lack of a dominant steering flow and so they could drop quite a bit of rain locally. Elsewhere across the southern Maritimes, an embedded TS risk exists within the broader precip shield that has enveloped the region. Later this afternoon, greater jet support advances east from New England and should create enough lift and charge separation to spark more lightning. Dewpoints remain fairly high near 15 at the noon hour. CAPE is relatively low today given the setup - so severe hazards are not forecast. Tomorrow is a different story across NB. The freezing levels will be much lower creating a possible hail-favoured setup. Additionally, if organized cells do form, they will bring an inherent wind risk. G90 are possible and are depicted by the yellow hazard area. This severe weather risk will be re-analyzed and potentially alerted for on Wednesday.

Thunderstorm Outlook for Today

Thunderstorm Outlook for Tonight

Thunderstorm Outlook for Tomorrow

Forecaster: Tirone.

Convective Outlook Valid for Today, Tonight and Tomorrow

Regional Impacts

Today

NB: Chance of some scattered thundershowers over western New Brunswick this afternoon with some locally heavy downpours.

Lab: Chance of some isolated thundershowers through central Labrador this afternoon.

NS/PEI/NFLD: None.

Tonight

NS/NB/PEI/NFLD/LAB : None.

Tomorrow

LAB: Risk of some marginally severe thunderstorms over southern Labrador in the afternoon with small hail, strong wind gusts, and locally heavy downpours.

NS: Risk of an elevated thundershower over southern mainland Nova Scotia through the day.

NB/PEI/NFLD: None.

 

Convective Discussion…

A ridge of high pressure sits over central Atlantic Canda this morning with a weak surface trough extending from central Maine up into central Quebec, just west of Labrador. This trough will be the main focus for any convection today, as it slowly begins to move east. A small but strong upper low over central Ontario will combine with a shortwave near New England and approach the trough this afternoon, which will act as the main trigger for convection. MLCAPE values over western New Brunswick are forecast to be around 500 to 750 J/kg today, with effective shear around 15 to 25 knots. One of the limiting factors however is how quickly the shortwave is advected East into New Brunswick, as well as some warm air aloft between 500 and 700 mb. This could limit the higher shear and some better thermodynamics from reaching the risk area until later this evening, which would lead to more isolated and short-lived thundershowers this afternoon. The risk for more organized storms could still increase into this evening however as the shortwave approaches, which could be capable of producing some locally heavy downpours of 10 to 20 mm per hour.

There is also a slight risk of some isolated thundershowers with a weak trough over central Labrador today which is in a similar environment to western New Brunswick, however there is a lack of moisture evident over this area which will reduce the risk of storms here today. Current surface observations show dewpoints only in the 5 to 7 degree range, with temperatures already above 20. Nonetheless, the potential for some isolated thundershowers exists which could produce some gusty winds.

Tonight, the shortwave will reach the Gulf of Maine, bringing with it the risk of an elevated thundershower over the marine areas west of Nova Scotia in the early morning hours. Into tomorrow, the shortwave will track across Nova Scotia, continuing to bring the chance for an elevated thundershower across the southern half of the mainland during the day and into the evening. Elsewhere, the upper low currently over central Ontario will sit over central Quebec by tomorrow morning with today’s surface trough now extending east from the upper low into southern Labrador. This will be the main focus for convection tomorrow, as MLCAPE values in the warm sector just south of the trough could reach 750 to 1000 J/kg by the afternoon. Slightly better moisture being advected in from the south and effective shear in the range of 20 to 30 knots should be sufficient to get some organized, marginally severe thunderstorms tomorrow afternoon. The surface trough is initially forecast to remain fairly stationary before eventually shifting south in the late afternoon/early evening. This in combination with an expected easterly storm motion could lead to some multi-cell training storms early in the day which would increase the risk of heavy rainfall for some areas. Some small hail and strong wind gusts are also possible with these storms. Luckily, the main risk area is expected to remain over unpopulated areas but could impact a few communities early in the afternoon.

 

Thunderstorm Outlook for Today

Thunderstorm Outlook for Tonight

Thunderstorm Outlook for Tomorrow

Forecaster: Copp

Convective Outlook Valid for Today , Tonight and Tomorrow

Regional Impacts

NS… Chance of thunderstorms today, some heavy downpours possible.

NB.. Chance of thunderstorms today and tomorrow. Heavy downpours possible with small hail.

PEI.. No thunderstorms expected.

Newfoundland.. No thunderstorms expected.

Labrador.. Low chance of thunderstorms expected tomorrow.

Convective Discussion

Instability will persist over western areas today as an upper trough slowly exits the region. CAPE values are expected to remain modest, reaching around 1000 J/kg, with generally weak low-level shear and deep-layer shear staying below 25 knots across most of New Brunswick.

As a result, severe thunderstorms are unlikely. However, isolated cells may still produce small hail and locally heavy downpours.

Looking ahead to tomorrow, shear will increase somewhat, but the relatively cool airmass will limit the available energy for convection. Non-severe showers or thunderstorms may once again develop over western areas. With limited heating and only modest increases in dew points expected in the coming days, overall conditions are not anticipated to change significantly.

Thunderstorm Outlook for Today

Thunderstorm Outlook for Tonight

Thunderstorm Outlook for Tomorrow

Convective Outlook Valid for Today , Tonight and Tomorrow

Regional Impacts

NB: Low chance of thunderstorms this evening, with little to no impacts expected.
NS: Some thunderstorms possible today, mainly over eastern areas. Locally heavy downpours and gusty winds possible.
Labrador: Low chance of thunderstorms today, no significant impacts expected.
Newfoundland: Low chance of thunderstorms today. Western/interior areas may see locally heavier rain.
PEI: Slight risk of thunderstorms today, with brief heavier showers possible.

Convective Discussion

A weak low pressure system over the region will continue to track northeastward today, with an associated surface trough moving across Nova Scotia through the day. Low-level convergence along this trough, as well as over parts of Newfoundland, will support isolated thunderstorm development.

Across Nova Scotia, the convective window will be relatively short-lived, ending by late afternoon as the trough exits. Slightly higher CAPE and shear in this region may support locally heavier rainfall rates and a risk of gusty winds in any storms that develop.

Over Newfoundland, thunderstorm activity may persist into the evening hours, with locally heavier downpours embedded within broader area of shower activity.

Over western Labrador, a weak thunderstorm cannot be ruled out, though no impacts are expected.

Looking ahead to Sunday into Monday, generally unsettled conditions will continue over New Brunswick and parts of Nova Scotia, with occasional weak thunderstorms possible.

Thunderstorm Outlook for Today

Thunderstorm Outlook for Tonight

Thunderstorm Outlook for Tomorrow

 

Mel Lemmon

Convective Outlook Valid for Today , Tonight and Tomorrow

Regional Impacts

NB.. Low chance of thunderstorms today, strong gusts possible if thunderstorms form.

NS.. Some thunderstorms possible tomorrow with heavier downpours.

Labrador.. low chance of thunderstorms today.

Newfoundland.. Low chance of embedded thunderstorms today over the east. Low chance of weak thunderstorms tomorrow interior.

PEI.. Slight risk of thunderstorms this evening.

 

Convective Discussion

Some dynamic support exists for convection today, though cooler temperatures and low dew points will limit updraft potential. Any storms that develop may produce locally strong wind gusts due to enhanced downdraft potential.

A low chance of embedded thunderstorms exists over eastern Newfoundland, with no expected impacts.

For tomorrow, a low-probability but higher-impact scenario exists over eastern Nova Scotia if training develops; localized rainfall rates near 25 mm/h are possible.

Sunday may be more active as another upper trough crosses the region. Modest instability and shear could support heavier downpours and small hail.

 

Thunderstorm Outlook for Today

Thunderstorm Outlook for Tonight

Thunderstorm Outlook for Tomorrow

Convective Outlook Valid for Today, Tonight and Tomorrow

Regional Impacts

Today

NB: Chance of an isolated thunderstorm over northern NB early this afternoon with small hail and strong wind gusts. Slight risk of an elevated thundershower with heavy downpours this evening over southwest NB.

NS: Slight risk of an elevated thundershower with heavy downpours this evening over extreme southwestern Nova Scotia.

LAB: Chance of an isolated thunderstorm over western Labrador this afternoon and early this evening with small hail and strong wind gusts.

PEI/NFLD: None.

Tonight

NB/NS/PEI: Chance of some elevated thundershowers overnight.

NFLD/LAB: None.

Tomorrow

NB/NS: Slight chance of some isolated thundershowers in the afternoon.

NFLD: Chance of some elevated thundershowers over southern Newfoundland through the day.

PEI/LAB: None.

 

Convective Discussion…

After a fairly active day across New Brunswick yesterday, a trough of low pressure will approach from New England this afternoon, reaching the western Maritimes by early this evening. There exists a few threat areas today, the first of which being associated with the aforementioned trough. Some lightning activity is already being observed across the eastern United States with this feature, and is expected to continue as it moves east through the day. The risk for thundershowers is expected to diminish in this trough as it approaches the Maritimes, however MUCAPE values may still rise to 250 to 400 J/kg over southwestern New Brunswick and Nova Scotia this evening. With near 40 knots of effective shear, there should be enough instability to allow for an elevated thundershower or two late this evening. The 12Z Upton, New York sounding indicated 43 mm of precipitable water, leading to the potential for some heavy downpours of 10 to 20 mm per hour over the risk area. Overnight, as the trough moves east across the Maritimes, there exists the potential for an elevated thundershower or two over PEI and Nova Scotia as well as southeast New Brunswick, but these are not expected to produce any significant hazards. This threat area will continue into southern Newfoundland through the day tomorrow.

Another area of interest exists over northern New Brunswick and western Labrador this afternoon, which is in a similar environment that produced some small hail and marginally severe storms over New Brunswick yesterday. SBCAPE values over this area could reach over 1000 J/kg, however a lack of effective shear (10 to 15 knots) will likely lead to a very short life span of any storms that develop this afternoon. Nonetheless, low freezing levels give the potential for some brief pea sized hail as the storms peak in intensity. The threat over New Brunswick will diminish into the late afternoon, as cloud cover from the approaching trough will cut off the energy needed to trigger these storms.

Tomorrow, the low pressure centre associated with the trough will cross northern New Brunswick. Given enough clearing over southern portions of the province, SBCAPE values could build up to 750 J/kg, giving enough energy to produce some isolated thundershowers in the afternoon. Even though effective shear is expected to be a bit higher than today (20 to 30 knots), fairly weak lapse rates should keep any storms from becoming severe.

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

NB: Isolated to scattered thundershowers giving brief strong wind gusts and small hail.

Lab: Isolated thundershowers over the extreme western sections.

NS/PEI/NL : Nil

Tonight

NB/NS/PEI/NL/LAB: Nil

Tomorrow

NB : Isolated thundershowers over northern and southern sections of the province.

NS: Isolated thundershowers along the western coast of the province.

Lab: Isolated thundershowers over the western sections.

Convective Discussion

Today, a weak riding over the Maritimes is expected to erode throughout the day. As this ridging erodes there is expected to be a sea-breeze form in the late afternoon which, along with day-time heating, will act as a trigger for convection in New Brunswick. The areas that have the formation of sea-breezes, and topographic enhancement will have the greatest chance to form storms that are able to produce longer lasting storms able to produce these winds near 70 km/h and hail over 1cm. With moderate dew points, and more than sufficient MUCAPE and MLCAPE, the main limiting factors for today is going to come down to windshear. There is troughing at the 850mb and 700mb levels which is allowing for convection to become more organized; however, without strong enough jet support todays storms are primed to be single cell and isolated in nature. Likewise for Western Labrador, the thunderstorms for today do not appear to have sufficient jet support to give rise to significant storms and are expected to be isolated in nature.

Tonight, with temperatures and sea-breezes being the most significant trigger for today, once temperatures begin to cool and the sea-breeze ceases the mechanisms for today’s storms will begin to shutdown. There is a risk in the early evening that any existing storms could become more elevated and persist slightly into the later evening hours. However, any storms that become elevated are expected run out of support quickly into the evening hours.

Tomorrow, there is an approaching frontal system coming from Ontario. With this system moving in there is a risk for isolated embedded thunderstorms as the warm sector approaches the Maritimes.  Additionally, as this system is approaching there is expected to be a Northwest flow that forms over the Eastern Maritimes and Southwestern Newfoundland regions. This flow could give rise to isolated thundershowers in upslope flow, however predictability on this setup producing thunderstorms is low and as such was not put into the outlook.

Thunderstorm Outlook for Today

Thunderstorm Outlook for Tonight

Thunderstorm Outlook for Tomorrow

Forecaster: Lambert/McArthur

Convective Outlook Valid for Today, Tonight and Tomorrow

Regional Impacts

Today

NS: Chance for embedded thundershowers across Cape Breton early this afternoon and isolated thundershowers in northern Nova Scotia this afternoon with brief wind gusts and a risk of small hail.

NB: Chance of isolated thundershowers in the southeast in the afternoon with a risk of brief wind gusts and small hail.

NFLD: Chance for elevated thundershowers.

PEI/Lab: None.

Tonight

Isolated embedded thundershowers over the Grand Banks and southern NL

NS/NB/PEI/LAB : None

Tomorrow

NB/NS: Isolated to scattered thundershowers giving brief strong wind gusts and small hail.

NL: Isolated embedded thundershowers over the Avalon Peninsula.

LAB/PEI: None

Convective Discussion

Today, a frontal system currently across the Gulf of St. Lawrence will slowly progress eastward and begin to slow down over Cape Breton and Southern Newfoundland tonight. The risk of embedded convection continues along the trough today and tonight. In behind the frontal system, clearing of the cloud with still moderate dew points will aid in increasing instability in the afternoon. There is a narrow corridor of Mixed CAPE nearing 500 J/Kg with effective shear of 20 to 30Kt due to an 850 mb LLJ giving rise to the possibility of some organized thundershowers from Southeast New Brunswick into central Nova Scotia late afternoon and early evening. Brief strong wind gusts and small hail less than 1 cm are expected. 

Tomorrow, a weak ridge over the Maritimes will erode, and with the aid of increasing moisture and convective temperatures along with an approaching jet streak from the west and sea breeze convergence, isolated to scattered showers with a risk of thundershowers will develop in the afternoon. The highest risk of storms is over central and northern New Brunswick, where freezing levels are fairly low and MUCAPE values are expected to reach 1500 J/kg. Shear is only light to moderate at or below 20kt, so expecting more pulse like storms with brief wind gusts, heavy rain and small hail of 1-2cm. Seabreeze convergence may also aid in a brief showers in the spine of NS, PEI and southern NB.

The risk of embedded thundershowers continues along the trough across the Avalon southeastward towards the Grand Banks as well tomorrow as the trough slowly pulls away to the southeast.

Thunderstorm Outlook for Today

 

Thunderstorm Outlook for Tonight

Thunderstorm Outlook for Tomorrow

Forecaster: McArthur

Convective Outlook Valid for Today , Tonight, Tomorrow, and Wednesday

Regional Impacts

Today

NS: Chance for elevated thunderstorms spanning Southwestern Nova Scotia through Central Nova Scotia. Risk for gusts of 60 to 70 km/h and rainfall of 20mm.

PEI: Chance for elevated thunderstorms spanning the province. Risk for gusts of 60 to 70 km/h and rainfall of 20mm.

NB: Chance for elevated thunderstorms in the Southeast sections of the province. Risk for gusts of 60 to 70 km/h and rainfall of 20mm. Slight chance of an Isolated thundershower over extreme Northwestern New Brunswick.

NFLD/LAB: Nil.

Tonight

NS: Chance for elevated thundershowers spanning Southwestern Nova Scotia through Central Nova Scotia. Risk for gusts of 60 to 70 km/h and rainfall of 20mm.

PEI: Chance for elevated thundershowers spanning the province. Risk for gusts of 60 to 70 km/h and rainfall of 20mm.

NB: Chance for elevated thundershowers in the Southeast sections of the province. Risk for gusts of 60 to 70 km/h and rainfall of 20mm. Slight chance of an isolated thundershower over extreme Northwestern New Brunswick.

NFLD/LAB: Nil.

Tomorrow

NS: Chance for elevated thundershowers spanning Central Nova Scotia through Cape Breton.

PEI: Chance for elevated thundershowers spanning the province in the morning.

NB: Chance for elevated thundershowers over the majority of the province.

NFLD: Chance for elevated thundershowers over the extreme Southwest and South-central regions of the province.

Lab: Nil

Wednesday

NS: Chance for isolated thunderstorms predominantly over the Central regions of the province.

PEI: Chance for isolated thunderstorms over the province.

NB: Chance for isolated thunderstorms over the interior of the province. Risks include gusts of 70-80km/h and hail near 2cm.

NFLD: Chance for elevated thundershowers over the Southern and Central regions of the province.

LAB: Nil.

 

Convective Discussion…

An approaching frontal system is progressing through the Atlantic Canada today is eroding the previously placed high pressure system throughout today and tomorrow.

Today, the main threat area will be in the Southeastern sections of New Brunswick and over most of mainland Nova Scotia where elevated thunderstorms could produce heavy downpours with rainfall possibly exceeding 20mm of rain and wind gusts of 60 to 70km/h. From ship observations there was reports of winds in excess of 60km/h. Current satellite imagery shows the approaching frontal system with embedded thunderstorms over the marine regions from overnight approaching the Nova Scotia coast. This should allow the continuation of MUCAPE to near 600 J/Kg, along with PWAT’s to remain near 30-40mm by this afternoon and progress eastward.

Tonight, as the frontal system progresses eastward bringing the elevated thunderstorms into Cape Breton and begin approaching Southern Newfoundland. Additionally, behind the frontal system there is expected to be a clearing in behind the system allowing for instability to approach New Brunswick allowing for further convection to occur. Thunderstorms in the clearing are expected to start off as surface based showers and becoming elevated overnight. This instability mixed with cloud-top cooling is expected to give rise to elevated thunderstorms.

Tomorrow, the frontal system from overnight will continue to progress eastward and begin to slow down over Cape Breton and Southern Newfoundland. In behind the frontal system tomorrow there is likely to be a narrow corridor of MUCAPE nearing 700 J/Kg with shear of 20 to 30Kt giving rise to the possibility of thundershowers from Southeast New Brunswick into Central Nova Scotia.  

Wednesday, as the frontal system has departed and began to diminish over Newfoundland the previous couple of days rainfall is expected to give rise to excess moisture that align with Jet streak approaching from the West to act as a trigger for more severe thunderstorms over the interior of NB. There remains some uncertainty with this setup as it does rely on how must moisture gets injected into the interior of New Brunswick from these next couple of days. Current computer guidance is indicating that within the interior of New Brunswick there could be a risk of thunderstorm with gusts in excess of 80 km/h and hail nearing 2 cm. This come from MUCAPE nearing 2,000 J/Kg and MLCAPE nearing 1,000 J/Kg along with relatively good shear throughout the profile.

Thunderstorm Outlook for Today

Thunderstorm Outlook for Tonight

Thunderstorm Outlook for Tomorrow

Thunderstorm Outlook for Wednesday

Forecaster: McArthur/Lambert

 

 

Convective Outlook Valid for Today, Tonight and Tomorrow

Regional Impacts

Today

NB: Risk of marginally severe thunderstorms over northwestern New Brunswick this afternoon capable of producing heavy downpours, strong winds, and some small hail.

NS/PEI/NFLD/LAB: None.

Tonight

NS: Slight chance of elevated thundershowers over southwestern Nova Scotia before morning.

NB: Chance of a few thundershowers over northern New Brunswick with locally heavy downpours.

PEI/NFLD/LAB: None.

Tomorrow

NS: Slight chance of some isolated embedded thundershowers over mainland Nova Scotia.

NB: Slight chance of an isolated thundershower over extreme northwestern New Brunswick.

PEI/NFLD/LAB: None

 

Convective Discussion…

An active couple of days are in store for Atlantic Canada as a trough approaches from the west and begins to erode a ridge of high pressure over the central Maritimes. Today, the main threat area will be in parts of northwestern New Brunswick, where some marginally severe thunderstorms are possible this afternoon. Some overnight convection is lingering over the area of interest, leading to some increased cloud cover, but current satellite imagery shows clearing off to the west over southern Quebec. This should allow MLCAPE values to rise near 1000 J/kg this afternoon over the northwestern portion of New Brunswick and with effective shear near 40 knots, some marginally severe thunderstorms are possible. One limiting factor in the intensity of these storms will be relatively moderate lapse rates, but given enough clearing early this afternoon, storms should have no issues firing. Given the weaker lapse rates, hail will not be much of a concern, but some decent PWAT values near 30 to 35 mm will lead to some heavy downpours in thunderstorms. In addition, there is potential for some strong wind gusts in the downdrafts of these storms. Without the 12Z sounding out of Caribou this morning, there isn’t a good sample of the current environment over the area, but the Maniwaka sounding from 00Z last night shows a relatively unstable airmass in a highly sheared environment. In addition, model tephigrams are indicating some curvature in the low level winds over northwestern New Brunswick this afternoon leading to a non-zero tornado risk, though this risk remains very low at this time. Severe thunderstorm watches may be issued early this afternoon as confidence increases.

Tonight, the trough will continue to slowly move east, reaching southwestern Nova Scotia by morning. With some weak mid-level instability expected overnight, some elevated thundershowers are possible here, in addition to northern New Brunswick. The trough will continue to move east through the day tomorrow, extending the risk for an elevated thundershower over parts of mainland Nova Scotia. The unstable airmass behind the trough may also lead to some isolated thundershowers over extreme northwestern New Brunswick in the afternoon.

 

Thunderstorm Outlook for Today

Thunderstorm Outlook for Tonight

Thunderstorm Outlook for Tomorrow

Forecaster: Copp