Convective Outlook Valid for Today , Tonight and Tomorrow

Regional Impacts

 

Today

NS/NB/PEI: Thundershowers giving potential significant rainfall amounts.

NFLD/LAB: Scattered thundershowers.

 

Tonight

NS/NB/PEI/NFLD/LAB: None.

 

Saturday

NFLD: A chance of thundershowers.

NS/NB/PEI/LAB: None.

 

Convective Discussion

A surface low pressure system and supporting upper low will continue to slowly move across Atlantic Canada today and then depart Newfoundland on Saturday. The main area of concern today is once again over Nova Scotia, New Brunswick and Prince Edward Island where MLCAPE values are expected to be near 1000 J/kg and the effective shear will be 20 to 25 knots. The main hazards with any storms that develop will be small hail, gusty winds and locally heavy downpours. Any storms that do develop will be slow moving so any heavy downpours may lead to significant rainfall accumulations.  On Saturday, CAPE values will be 500 J/kg or less and will give a chance of thundershowers for Newfoundland.

Thunderstorm Outlook for Today

 

Thunderstorm Outlook for Tonight

Thunderstorm Outlook for Tomorrow

Convective Outlook Valid for Today , Tonight and Tomorrow

Regional Impacts

 

Today

NS/NB/PEI/NFLD/LAB: Scattered thundershowers.

 

Tonight

NS/NB/PEI: Chance of thundershowers.

NFLD/LAB: None.

 

Friday

NS/NB/PEI/NFLD/LAB: Scattered thundershowers.

 

Convective Discussion

A trough of low pressure and supporting upper low will slowly move across Atlantic Canada today and Friday. The main area of concern today is over Nova Scotia and New Brunswick where MLCAPE values are expected to be 1000-1500 J/kg and the shear will be 20 to 30 knots. The main hazards with any storms will be small hail, gusty winds and locally heavy downpours. Any storms that do develop will be slow moving so any heavy downpours may lead to significant rainfall accumulations.  On Friday, any potential impacts are expected to less than today due to lower CAPE, shear and precipital water values.

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 thundershower within a greater area of showers in central and southern NB this afternoon and evening. Main hazard is simply lightning.

LAB/NFLD: Chance of scattered thunderstorms over parts of Labrador today, and Nfld. Heavy downpours are possible.

Tonight

Gulf of St. Lawrence waters: Slight chance of an isolated thunderstorm cell to develop in the late evening and carry into the overnight hours.

Western Labrador: Isolated non-severe thundershowers possible before noon on Thursday, in area of showers.

Tomorrow

Atlantic Canada: Chance for numerous embedded thunderstorms with locally heavy downpours and potentially a few gusty winds.

Convective Discussion…

A persistent trof line continues to affect Labrador and Nfld today, bringing the chance of a few thundershowers. These cells will have ample moisture to work with, but not much lift in comparison. The prevailing cloud deck is the competition. Over the Maritimes, parts of NB are forecast to destabilize this afternoon (according to the high resolution model suite). Again, the storms have limiting CAPE today.

Tomorrow is looking to be a different story. The atmosphere is forecast to moisten even further in the next 24hrs – bringing Pwats on the Atlantic coast of NS up to 35 by tmrw morning. Thunderstorms that develop tomorrow within the broader precip field will enhance local rainfall totals further. This will be monitored closely (Rain Rates already being flagged near 30 to 40 mm/h). Some early day cells could also bring gusty winds if they can get into clearer skies, before the storm mode becomes clustered.

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/NS/PEI: Chance of scattered thunderstorms over the central Maritimes this afternoon with small hail, strong wind gusts, and heavy downpours.

LAB: Chance of scattered thunderstorms over eastern Labrador today with strong wind gusts and locally heavy downpours.

NL: Slight chance of an embedded thundershower over southwestern Newfoundland this afternoon.

Tonight

NL: Slight chance of an embedded thundershower over southwestern Newfoundland tonight into tomorrow morning.

NB/NS/PEI/LAB: None.

Tomorrow

NL/LAB: Chance for scattered thunderstorms across Newfoundland and parts of Labrador tomorrow with locally heavy downpours.

NB/NS/PEI: None.

 

Convective Discussion…

This morning, an upper trough extends from a low over the Labrador Sea back through northern Quebec and into Hudson Bay. South of this feature, a shortwave is moving into northern New Brunswick which will spin up a surface low by this afternoon. These will be the main drivers for convection in Atlantic Canada today. Over southeastern Labrador, clear skies this morning will pave the way for instability to increase to near 750 J/kg MLCAPE by early this afternoon, however a lack of effective shear (10 to 20 kts) over the region will likely keep any storms from becoming organized. Thus heavy downpours and some strong wind gusts are the main hazards here today. In the Maritimes, the surface low over New Brunswick will pull a cold front across the province this afternoon. Better dynamics will be in play here, with a good low level jet forecast to set up as well as a 500 mb jet moving across New England and into Nova Scotia, leading to effective shear of 30 to 40 knots by this afternoon. PWATs of 32.5 mm have been observed at the 12Z Yarmouth sounding this morning, which could build to near 40 mm over the area of interest today. Given enough clearing this morning, instability is forecast to increase upwards of 1000 J/kg. While thunderstorms are expected to fire across most of the Maritimes today, the best chance for severe storms will be in eastern New Brunswick and PEI in the warm sector closer to the low centre. One of the limiting factors for Nova Scotia will be the timing of the cold front moving through as well as some drier air present over the region.

Tonight, the low over New Brunswick will move out over the Gulf of St. Lawrence before moving through the Strait of Belle Isle tomorrow. Some elevated thundershowers will be possible around the low tonight and into tomorrow morning as it pushes into western Newfoundland. Some heavy downpours will be possible tomorrow as the cold front crosses the province but mainly cloudy conditions will keep the instability from building , this should keep rainfall rates around 10 to 20 mm per hour in the strongest cells.

 

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

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