Convective Outlook Valid for Today, Tonight and Tomorrow

Regional Impacts

Today

LAB: Chance of some scattered thunderstorms over western Labrador today capable of producing strong wind gusts and heavy downpours.

NB: Slight chance of an isolated thundershower over extreme northwestern NB this evening.

NL: Slight chance of an elevated thundershower later today over western Newfoundland.

NS/PEI: None.

Tonight

NB: Chance for some elevated thundershowers over northern NB overnight into tomorrow morning capable of producing some heavy downpours.

NS/PEI/NL/LAB: None.

Tomorrow

NB/NS/PEI: Chance for some scattered thunderstorms over the central Maritimes in the afternoon capable of producing strong wind gusts, small hail, and heavy downpours.

LAB: Chance for some scattered thundershowers over southeastern Labrador tomorrow capable of producing some strong wind gusts and heavy downpours.

NL: Slight chance of an isolated thundershower over western Newfoundland late in the day.

 

Convective Discussion…

This morning, an upper low sits over western Labrador with a trough extending south into western Newfoundland, which will very slowly move northeast today to lie over the Labrador Sea by tomorrow afternoon. Behind this feature, a weak ridge is beginning to erode as it moves into the Maritimes due to an amplifying shortwave currently traversing the eastern Ontario and southern Quebec border. The upper low over Labrador will be the main driver for convection today in Atlantic Canada. Some clearing is evident over southwestern Labrador this morning, which should allow MLCAPE values to rise near 500 to 750 J/kg. There is however a lack of wind shear today over the region, with the main jet well south of the main risk area. This will likely lead to a short life span of any storms that fire today, and are not expected to reach severe criteria. The main hazards with any storms here will be some strong wind gusts and brief heavy downpours. Some Elevated thundershowers are also possible along the trough extending into western Newfoundland today. There also exists the small risk of an isolated thundershower over northwestern New Brunswick as well, however the lack of a trigger will likely keep any storms from firing here until later this evening.

Tonight, the aforementioned shortwave over eastern Ontario will approach western New Brunswick. With a strong 500 mb jet extending from southern Ontario through the southern Maritimes, convection is expected to maintain itself overnight as it moves in from Maine. Some locally heavy downpours will be possible overnight and into tomorrow morning in northern New Brunswick. By tomorrow afternoon, a low is forecast to spin up over central New Brunswick, with a warm front extending across the Gulf of St. Lawrence into southwestern Newfoundland. Some elevated thundershowers will be possible along the warm front, but the higher potential for thunderstorms will be in the warm sector over PEI, southeast New Brunswick, and western Nova Scotia. Here, given enough clearing before the cold front pushes through, MLCAPE values could rise upwards of 1000 J/kg. In combination with the strong jet over the region aiding in 30 to 40 knots of effective shear, some organized thunderstorms will be possible tomorrow afternoon that could possibly become severe given enough instability builds. PWATs are forecast to rise near 40 mm over the area of interest tomorrow which could lead to some locally heavy downpours, in addition to the potential for some strong wind gusts and small hail. Over southeastern Labrador, some scattered thundershowers could develop in the afternoon along the lingering trough extending down from the Labrador Sea. Once again, shear over this area is limited, so storms will not be very long-lived, but some brief strong winds gusts and locally heavy downpours area possible.

 

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: Scattered thunderstorms giving heavy rain, strong winds and small hail.

NS/PEI/LAB: Isolated thunderstorms giving heavy rain and brief strong winds.

NL: None

Tonight

Gulf of St. Lawrence/PEI/LAB: Isolated thunderstorms giving heavy rain.

NS/NB/NL: None

Tomorrow

LAB: Scattered thunderstorms giving heavy rain, small hail and strong wind gusts.

NB: Isolated thunderstorm giving heavy rain.

NS/PEI/NL: None

Convective Discussion

A mid-level trough moves east from Quebec into New England and New Brunswick today. With daytime heating and clearing expected behind the morning convection across New Brunswick along the 850mb thermal ridge, further destabilization is anticipated. A cold front will also move from northern Maine into New Brunswick later in the afternoon. There is increasing ingredients in play over New Brunswick such as increasing effective shear to 30-40kt, MLCAPE possibly reaching 2000 J/kg, and the area being near the left exit region of the 250mb jet. There is the potential for more organized convection mainly in the form of bowlines given strait-line shear, but a possible supercell cannot be ruled out. Storms have the potential to give small hail, very heavy downpours, and strong wind gusts as they track towards the east with a mean flow of 40 km/h. Convection is also expected in western Labrador and northern Nova Scotia influenced by the higher terrain. Thunderstorms may persist into the Gulf of St. Lawrence, PEI and western Labrador tonight as the cold front continues eastward. 

For tomorrow, the trough continues across Labrador with the weakening cold front extending southeastward into Newfoundland. There is a risk of a thundershower in northwest New Brunswick ahead of the next short-wave trough tracking across the Great Lakes and reaching New Brunswick by Tuesday morning.

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:  Scattered thunderstorms giving heavy rain and brief strong wind gusts.

NL/LAB: None

Tonight

NS/NB/LAB: Isolated thunderstorms giving heavy rain.

NL: None

Tomorrow

NB: Scattered thunderstorms giving heavy rain, strong winds and small hail.

NS/PEI/LAB: Isolated thunderstorms giving heavy rain and strong winds.

NL: None

Convective Discussion

A short-wave trough is advancing into New Brunswick and Nova Scotia today while a ridge of high pressure holds south of the Maritimes and the stalled upper low southeast of Newfoundland is slowly moving further east. Overall instability will increase with daytime heating under a still under rather hot and humid air mass. Some slow-moving thunderstorms have already begun to pop over the higher terrain in New Brunswick this morning with rainfall rates of upwards of 35 mm/h and convection over southern Maine and is moving towards western Nova Scotia. With MCAPE potentially reaching 1500 J/kg, precipitable water near 50 mm and effective shear near 25kt, multicell storms are most likely capable of heavy downpours and brief strong wind gusts. The slow-moving nature of the storms will add to the risk of heavy downpours.

For tomorrow,  a mid-level trough moves east from Quebec into New England and New Brunswick with the environment further destabilizing across the Maritimes and western Labrador. A cold front is expected to move from northern Maine into New Brunswick in the afternoon. With effective shear increasing to 30-40kt MLCAPE exceeding 1500 J/kg, there is the potential for more organized convection in the form of bowlines or potential supercells giving small hail, heavy downpours, and strong wind gusts. 

Thunderstorm Outlook for Today

Thunderstorm Outlook for Tonight

Thunderstorm Outlook for Tomorrow

Convective Outlook Valid for Today, Tonight and Tomorrow

Regional Impacts

Today

Labrador: advancing trof bringing in slightly better dynamics for taller and more organized thunderstorms. Gusty winds, small hail, and brief but heavy downpours are possible. This has already started over southern sections this AM.

NB: Thunderstorms are possible in the afternoon and evening as the cap is finally able to break in this airmass (mainly tied to geography). Small hail and heavy downpours are possible.

NS: Guidance is suggesting the cap will break in the afternoon for an isolated region along the “spine” and the South Shore. Brief, heavy downpours are possible. These cells will move south over the coastline/water late in the day. They are forecast to remain isolated.

Tonight

None expected over land areas.

Tomorrow

Labrador: repeat of dynamics from Friday but less moisture to work with over western areas.

NB: Scattered thunderstorms are possible again in the afternoon and evening. Southern sections look to be more airmass, and northern areas forced by an advancing trof. Details will be added on Saturday regarding these specifics.

NS/Bay of Fundy: Numerous scattered thunderstorms are expected along the E-W spine and northern areas of NS. The main hazards will be small hail and heavy downpours for areas under the cells.

Convective Discussion

The story for the Maritimes today continues to be the high heat and humidity. Dew points this morning are reaching 21 in places. This is fuel for convective weather, if the cap can break. It seems that it will across NB this afternoon, and isolated western parts of NS (using E townships of Quebec as an upstream reference from yesterday). These cells will bring brief heavy downpours. There is less forest fire smoke present in the mid levels of the atmosphere than yesterday, but it is not zero. Storms that fire today are largely expected to be terrain driven.

In Labrador, the organization is quite a bit better for multi-cells over southern sections, forced along the advancing circulation/trof. Formation is evident already on visible satellite. These cells could produce strong wind gusts, and small hail along with frequent lightning and heavy downpours. Northern areas of Labrador are only expected to see single cell or embedded convection similar to yesterday.

Tomorrow will bring a renewed and more broad convective risk to Atlantic Canada. With the high moisture and forcings approaching from the west acting to destabilize the airmass further, multiple areas of thunderstorms are expected – tied to geographic and synoptic triggers. The exact timing and locations will be clearer tomorrow morning on water vapour imagery, but it is important to note that if any cells persistently train over one area, quite a bit of rainfall could occur in a short amount of time. Pwats are expected to be very high.

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

Labrador: slight risk of a thundershower along an elongated trof in western areas stemming from Quebec, similar to yesterday.

Tonight

None expected over land areas.

Tomorrow

Labrador: advancing trof bringing in slightly better dynamics for taller and more organized thunderstorms. Gusty winds, small hail, and brief but heavy downpours are possible.

NB: Thunderstorms are possible in the afternoon and evening as the cap is finally able to break in this airmass (mainly tied to geography). Small hail and heavy downpours are possible.

NS: Guidance is suggesting the cap will break in the afternoon for an isolated region along the “spine” and the South Shore. Heavy downpours are possible. These cells will move south over the coastline/water late in the day.

Convective Discussion

This morning, Nfld is in the overcast and drizzle regime thanks to the occluded low churning in the Atlantic to their east. Western Labrador has a chance of seeing some thundershower activity forced by the very elongated trof in Quebec.

The Maritimes are well into day 2 of their heat event under a strong and humid ridge of high pressure. Dew points are becoming tropical and are near 19 in places this AM. Thunderstorm activity is not forecast today in these stable conditions. However, tomorrow there are signals that this may start to break down. And so, TS risks are being added in some areas on Friday. MLCAPE tomorrow is 1000 in places, and 20-30kts effective shear. This will be monitored closely to see where the subtle triggers set up tomorrow.

Thunderstorm Outlook for Today

Thunderstorm Outlook for Tonight

Thunderstorm Outlook for Tomorrow

Forecaster: Tirone.