Convective Outlook Valid for Today , Tonight and Tomorrow

Regional Impacts

Isolated thundershowers over a portion of the southern GB today.

 

Tonight and Tuesday offers the potential for waterspouts for a good portion of the Gulf of St. Lawrence and into southern Gulf-Port au Port.

 

Convective Discussion

A weak frontal wave will give isolated thunderstorms today over a portion of the southern Grand Banks today. A fairly cold upper trough will be moving down from Quebec and Labrador tonight and Tuesday that will create favourable conditions for non-tornadic waterspouts for a good chunk of the GLFSTLAWR and into the Port au Port Peninsula area.

 

OTWZ nil sig wx xpctd.

 

Thunderstorm Outlook for Today

 

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Thunderstorm Outlook for Tomorrow

 

Jeremy

Convective Outlook Valid for Today , Tonight and Tomorrow

Regional Impacts

Risk of a thunderstorm in western LAB, NW NB and SW NS later today.

 

Risk of thundershowers tonight along most of the ATL coast of NS.

 

Risk of thundershowers later today and tonight over the SRN GB.

 

Convective Discussion

3 separate features evident in SAT imagery: one being a weak surface low southeast of MRTM waters that will move up and over the southern GB later today and tonight giving the risk of thundershowers. The second feature will be an approaching cold frontal trough that is currently in Quebec. This will likely produce isolated thunderstorms upstream today, with the chance that one or 2 cells survive and make it to far western LAB and NW NB. Gusty winds and brief downpours are possible. The 3^rd feature will be a surface trough that is currently sliding towards NS. There is a chance of some late day and overnight thundershowers associated with it near Atlantic coastal NS. However there is no history with this so confidence on that happening is on the low side. Locally heavy downpours would be the only concern.

 

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Jeremy

Convective Outlook Valid for Today , Tonight and Tomorrow

Regional Impacts

Slight risk of a thundershower tonight for NB.

 

Risk of a late day thunderstorm for W/NW NB Sunday giving gusty winds and heavy downpours. Slight risk of a thundershower Sunday evening for far southwestern NS.

 

Convective Discussion

Quiet today right across the board as the MRTMS and NL are under the influence of a ridge of high pressure. A frontal trough will give showers to most of Labrador but no lightning is expected. The same frontal trough will slide down over NB tonight giving just the slight risk of a thundershower overnight and early Sunday with the aid of cloud top cooling. Sunday will give the risk of a late day thunderstorm to W/NW NB as a secondary frontal trough rapidly swings in upstream from Quebec. This front could give some strong wind gusts and locally brief heavy downpours. The aforementioned trough impacting NB tonight will give some showers and risk of thundershowers to NS Sunday night.

 

Thunderstorm Outlook for Today

 

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Jeremy

Convective Outlook Valid for Today, Tonight and Tomorrow

Regional Impacts

 

Today

Labrador: Chance of isolated thundershowers.

NB/NS/PEI/NL: None.

 

Tonight

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

 

Tomorrow

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

 

Convective Discussion

 

A cold front will sweep across Labrador today from Quebec and continue through the Maritimes and Newfoundland on Wednesday. There is a slight risk of convection over western and northern Labrador today, but the air mass is expected to be too stable with warming 500mb temperatures as the font continues tonight and Wednesday across the Maritimes. Nonetheless, there could still be some heavier pockets of rain in TCUs with precipitable water increasing to 40 mm over the Maritimes, but the front is forecast to move through quickly, which will limit rainfall amounts.

 

This cold front ushers in a cooler, drier air mass under a strong high pressure system that will suppress any convection in the region until at least the end of the week.

 

 

Thunderstorm Outlook for Today

 

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Thunderstorm Outlook for Tomorrow

 

 

 

Roberta McArthur

 

 

 

Convective Outlook Valid for Today , Tonight and Tomorrow

Regional Impacts…

 

Today

NB/NS/Labrador: Chance of non-severe thunderstorms.

PEI/NL:  None.

 

Tonight

Labrador: Chance of embedded thunderstorms.

NB/NS/PEI/NL:  None.

Tuesday

Labrador: Chance of embedded thunderstorms.

NB/NS/PEI/NL: None.

 

Convective Discussion

An upper low is expected to slowly move across the Maritimes today. Pop-up convection is expected across cloud free areas under the upper low today. The convection may become lightning producing across New Brunswick and northern Nova Scotia. There is little in the way of 0-6 km shear (10-15 kts) but moderate precipitable water values (25 to 35 mm) are occurring, so some locally heavy downpours are possible in slow moving storms. MLCAPE is forecast to be 1000-1500 J/kg today. An approaching trough of low pressure may give some embedded thundershowers across western Labrador on Tuesday.

 

A low pressure system tracking northeastward well south of Nova Scotia may give embedded lightning over portions the marine district today and tonight.

 

Thunderstorm Outlook for Today

 

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Convective Outlook Valid for Today, Tonight and Tomorrow

Regional Impacts

 

Today

NB/LAB…Isolated thundershowers giving locally heavy downpours of 10 to 15 mm/h.

NS/PEI…None

 

Tomorrow

NB…Isolated to scattered thundershowers giving locally heavy downpours of 15 to 25 mm/h.

LAB… Isolated thundershowers giving locally heavy downpours of 10 to 15 mm/h.

NS/PEI…None

 

Convective Discussion

 

An upper low is expected to slowly move across southern Quebec today then south into Maine tomorrow. Clear skies across much of Maine, New Brunswick and southern Labrador this morning will aid in increasing instability and allow for pop-up convection ahead and near the centre of this low this afternoon and again tomorrow. There is little in the way of shear but with there will be an increase in precipitable water (25 to 35 mm) by tomorrow over western New Brunswick, so some locally heavy downpours are possible in slow moving storms. MLCAPE is forecasted to be near 1000 J/kg over much of New Brunswick tomorrow, but shear remains near 15KT, so not expecting severe thunderstorms to develop beyond heavy downpours. The amount of surface heating and a warm cap near 700 mb will be the main factors if convection develops over the spine of Nova Scotia on Monday afternoon.

 

A low pressure system will develop on Monday south of the Maritime marine district and track northeastward towards eastern Newfoundland Monday night. This low may have some embedded convection, especially near and ahead of the low centre.

 

Thunderstorm Outlook for Today

 

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Thunderstorm Outlook for Tomorrow

 

 

Roberta McArthur

 

 

Convective Outlook Valid for Today, Tonight and Tomorrow

Regional Impacts

 

Today

NL/LAB… Isolated thundershowers with be locally heavy downpours of 10 to 20 mm/h and small hail of 1 cm or less. There is also the possibility of cold core funnels.

 

Tomorrow

NB/LAB…Isolated thundershowers giving locally heavy downpours of 10 to 20 mm/h.

 

Convective Discussion

A rather cold upper low continues eastward this morning over Newfoundland and into the Labrador Sea with a risk of some isolated thundershowers in northern and central Newfoundland and southeastern Labrador today. This area has a history of waterspouts over the Gulf of St. Lawrence and with continued cold air aloft, relatively warm surface land and water and topographic influences will aid in the potential of cold air funnels today over Newfoundland as this low continues eastward.  With MLCAPE values around 800 J/kg, and weakening strait line bulk shear of 15KT, any thundershowers that develop are unlikely to become severe. Nonetheless, some brief heavy downpours of 10 to 20 mm/h will be possible and with lower freezing levels given the cold air aloft, there is a risk of small hail.

 

Another weak low is expected to move towards western New Brunswick and Labrador from Quebec tomorrow. Daytime heating and some instability will allow for pop-up convection ahead and near the centre of this low is where the risk of thunderstorms will be. There is little shear but moderate precipitable water so some locally heavy downpours are possible.

 

Thunderstorm Outlook for Today

 

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Roberta McArthur

 

 

 

Convective Outlook Valid for Today, Tonight and Tomorrow

Regional Impacts

NB/NS/PEI/NL… Slight chance for some isolated thundershowers today across central Atlantic Canada. Main hazard will be locally heavy downpours of 10 to 20 mm/h.

 

Convective Discussion…

An upper low moving northeast into the Gulf of St. Lawrence this morning brings the risk for some isolated thundershowers across central Atlantic Canada today. Convection will be focused near the center of the upper low, though better bulk shear values (40 to 50 knots) to the east, closer to the Cabot Strait, may allow for some thundershowers to develop over Cape Breton and western Newfoundland later this afternoon. MLCAPE values are quite low across the region today, less than 750 J/kg, so thundershowers are unlikely to become severe. Nonetheless, some brief heavy downpours of 10 to 20 mm/h will be possible.

 

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Copp

Convective Outlook Valid for Today, Tonight and Tomorrow

Regional Impacts

NB… Slight chance for some isolated thundershowers this afternoon and evening. Main threat is locally heavy downpours of 10 to 20 mm/h.

NS/PEI/NL… None.

 

Convective Discussion…

An upper low currently sitting over the St. Lawrence Valley will be the main trigger for convection today. The low will slowly begin to move east this afternoon, with convection expected to fire in Maine before crossing the border as the low moves into western New Brunswick. Instability is expected to be quite limited today, with only up to 500 J/kg of MLCAPE forecast this afternoon. Modest bulk shear of 15 to 25 knots should inhibit most storms from becoming too organized, so severe weather is not expected today. Nonetheless, the upper low should be enough to fire a few weak thunderstorms later this afternoon in western New Brunswick once convective temperatures (20 C) are reached, with locally heavy downpours of 10 to 20 mm/h being the main risk.

 

This low will continue to move east tonight, to lie over Anticosti Island by tomorrow afternoon. As such, most of the convection will be centred over the Gulf of St. Lawrence tomorrow. As the low moves into the Gulf early tomorrow morning, relatively warm waters of 18 to 20 C in the area of interest, and the cold upper low, should provide enough instability and vorticity for convection. With this, there exists a slight chance for a waterspout off the Acadian coast of New Brunswick in the morning hours.

 

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Copp

Convective Outlook Valid for Today , Tonight and Tomorrow

Thunderstorm Outlook for Today

 

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Convective Outlook Valid for Today , Tonight and Tomorrow

Regional Impacts

Maritimes… Isolated thunderstorms giving 15-30mm, some potential for torrential downpours today. Some stronger wind gusts possible.

Newfoundland… Isolated thunderstorms giving 15-30mm, some potential for torrential downpours today. Some stronger wind gusts possible. Heavier downpours along south coast possible overnight.

 

Convective Discussion

Most of the region will remain under this moist airmass for today and into tomorrow for Newfoundland. The most probable areas for isolated severe storms have been highlighted but it should be noted that intense rainfall could set up in various locations today and warnings ,if required, would be very short fused. There are a few areas that lend themselves to a slightly higher potential due to severe thunderstorms, including interior Newfoundland and central parts of the Maritimes. The break up of the cloud is already happening in these areas and along with the solar heating there are potential triggers for convective initiation in these areas. Surface based CAPE is likely to exceed 1000 j/kg in these areas and with the approaching upper trough at 500 there is ample shear of >50 kts for longer lived thunderstorms. Despite some of these values, updrafts are still somewhat weak with thin CAPE that could be sheared off initially, possibly impeding the deeper convection somewhat.

 

The other area of interest will be likely be along the south coast of Newfoundland tonight as the atmospheric river sets ups just over the eastern part of the island, the instability may be high enough to bring rainfall rates over 40mm/hr, radar rainfall estimates and convection will have to be closely monitored through the evening and overnight.

 

Thunderstorm Outlook for Today

 

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Convective Outlook Valid for Today, Tonight and Tomorrow

 

Regional Impacts

 

Today

NS/PEI/NL…Heavy downpours with rainfall rates of 20 to 40 mm/h with slight risk of embedded convection.

NB…Slight risk of a thundershower over northwestern regions.

 

 

Tonight

NL/LAB…Heavy downpours associated with Ernesto to affect southeastern Newfoundland.

NB…Locally downpours with risk of embedded thunderstorms possible.

 

 

Tomorrow

NB/PEI…Locally downpours with risk of embedded thunderstorms possible.

NS/NL/LAB…None.

 

 

Convective Discussion

The centre of Ernesto is beginning to track into the southern marine waters and northeast towards the Avalon Peninsula of Newfoundland tonight. Some bands of heavy rain with a few embedded thunderstorms have begun to move north into Nova Scotia this morning and southern Newfoundland well ahead of Ernesto. With precipitable water near 55 mm over this area, rainfall rates could be high at times today. As the actual storm moves south of the Avalon tonight, rainfall rates are expected to be high for a short period of time. There is a slight risk of embedded thunderstorms with the passage of this storm as well today and overnight.

 

A shortwave trough over southern Quebec and New England will slowly move eastward to lie over New Brunswick tomorrow then stall across the region. Heavy downpours are possible with this especially over northwestern New Brunswick as this trough slows further.

 

Thunderstorm Outlook for Today

 

Thunderstorm Outlook for Tonight

 

Thunderstorm Outlook for Tomorrow

 

 

Roberta McArthur

 

 

 

Convective Outlook Valid for Today, Tonight and Tomorrow

Regional Impacts

 

Today

NL/LAB… Scattered thunderstorms possible across Labrador today with downpours of 15 mm/h.

NS/NB/PEI… None.

 

Tonight

NS…Heavy downpours with risk of embedded thunderstorms possible giving rainfall rates of 20 to 40 mm/h.

 

Tomorrow

NB…Slight risk of a thundershower over northwestern regions.

NL/LAB…Heavy downpours ahead of Ernesto to affect southern Newfoundland.

NS/PEI…Risk of heavy downpours but thunderstorm risk is low at this time.

 

 

Convective Discussion

An upper trough stretches from southern Ontario northeastward into Labrador that is slowly moving eastward but will slow down as it begins to interact with Tropical Storm Ernesto over the next few days as the storm tracks over the southern marine waters. A shortwave trough over southern Ontario has been fairly active with convection yesterday and continued overnight into this morning. This shortwave will slowly drift eastward and weaken somewhat today. A secondary trough south of Ungava Bay this morning will help stretch moisture into western Labrador. MLCAPE values in southern Labrador are forecast to rise upwards of 1000 J/kg today along with mainly linear bulk shear values of 20 to 30 knots. With precipitable water forecast to increase to 30 mm, the main hazard today will be torrential downpours of 15 mm/h but brief strong wind gusts are possible if discrete cells organize into lines.

 

As Hurricane Ernesto continues northward and begins to enter the southern maritime waters early on Monday, an area of heavy downpours is possible well ahead of the circulation that will affect the southern maritime provinces on Monday with a slight risk of embedded thunderstorms mainly for overnight and early Monday with the help of cloud top cooling. Precipitable water is forecast to increase above 55 mm across Nova Scotia then east towards southern Newfoundland by Monday night.

 

Thunderstorm Outlook for Today

 

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Thunderstorm Outlook for Tomorrow

 

 

Roberta McArthur

 

 

 

Convective Outlook Valid for Today, Tonight and Tomorrow

Regional Impacts

NL… Scattered severe thunderstorms possible across southern Labrador today. Main hazards are strong wind gusts of 70 to 90 km/h, heavy downpours of 25 to 35 mm/h, and 1 to 2 cm hail.

NS/NB/PEI… None.

 

Convective Discussion…

After a busy couple of days in the Maritimes, the focus shifts to southern Labrador today, where an upper trough with some diffluent upper level flow brings the risk for some scattered severe thunderstorms this afternoon. MLCAPE values are forecast to rise upwards of 1500 J/kg today over southeastern Labrador, leaving plenty of fuel for thunderstorms to work with. In addition, bulk shear values of 25 to 35 knots in the same area increases the potential for some of these storms to become severe. Shear is expected to be fairly linear, however some curvature of the low level winds is possible early on in the afternoon. As such, a discrete supercell or two cannot be ruled out early this afternoon, before storms become more linear later on. The main hazards today will be torrential downpours of 25 to 35 mm/h, strong wind gusts of 70 to 90 km/h, and 1 to 2 cm hail.

 

Thunderstorm Outlook for Today

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Copp

Convective Outlook Valid for Today, Tonight and Tomorrow

Regional Impacts

NS… Scattered thunderstorms today with heavy downpours of 20 to 30 mm/h.

NB… Slight chance of an isolated thundershower over northern New Brunswick this afternoon, with downpours of 10 to 20 mm/h.

NL… Slight chance of an isolated thundershower this afternoon over extreme southern Labrador, with downpours of 10 to 20 mm/h.

PEI… None.

 

Convective Discussion…

The upper low that brought severe thunderstorms to parts of the Maritimes yesterday will move east over Nova Scotia today. This once again brings the risk for some scattered thunderstorms that will be capable of producing heavy downpours. MLCAPE values over 1000 J/kg will provide ample instability to get convection going under the upper low this afternoon, weaker bulk shear and lower PWAT values over central mainland NS keeps the risk slightly lower here. Higher PWAT values of 30-35 mm over eastern mainland NS and parts of Cape Breton increase the potential for severe thunderstorms here, with rainfall rates of 20 to 30 mm/h possible. Localized flooding will also be a risk under storms that remain slow moving today.

There also exists a very slight risk for an isolated non-severe thundershower in northern New Brunswick and extreme southern Labrador this afternoon. Smoke aloft over Labrador in addition to a thermal ridge above 700 mb may inhibit convection here today as storms will struggle to get going.

 

Thunderstorm Outlook for Today

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Copp

Convective Outlook Valid for Today , Tonight and Tomorrow

Regional Impacts

NS… Scattered thundershowers possible today with heavy downpours of 20 to 30 mm/h.

NB… Isolated thunderstorms possible this afternoon with heavy downpours of 15 to 25 mm/h.

PEI/NL… None

 

Convective Discussion

Today, an upper low sits stalled over the central Maritimes with two thunderstorm risk areas existing today with this feature; the first located over Nova Scotia, and the second over northwestern New Brunswick. MLCAPE values of 1000 J/kg are similar over both areas of interest, however better dynamics (35 to 40 kts of bulk shear) can be found over northwestern New Brunswick, so a few discrete thunderstorms are possible here this afternoon. These storms will have the potential to produce locally heavy downpours of 15 to 25 mm/h. In Nova Scotia, similar to yesterday, storms are expected to be more stationary leading to an increased risk of higher rainfall accumulations over localized areas today. Some of these storm may have the potential to produce rainfall rates of 20 to 30 mm/h, with higher accumulations possible under stationary cells.

 

Thunderstorm Outlook for Today

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Copp

Convective Outlook Valid for Today , Tonight and Tomorrow

Regional Impacts

NB… Isolated thunderstorms giving some heavy downpours, mainly for western areas.

PEI… Isolated thunderstorms giving some heavy downpours, a chance of a funnel cloud east or potentially a waterspout over eastern marine areas.

NS.. Some thunderstorms, some potential for locally amounts over 25mm. A chance of a funnel or possible waterspout west of Cape Breton.

 

Convective Discussion

Yesterday back building thunderstorms tended to produce more local rain than expected, while not as likely there is still a chance that we may have more of these weak, slow moving, storms that seem to reform over areas of convergence/terrain and linger longer than would normally be expected with these types of thunderstorms. For the most part the airmass is fairly similar to yesterday with CAPE values ~ 1000 J/kg and surface Td’s in the mid teens. Rainfall rates could once again exceed 30mm/hr, if storms end up back building once again local amounts could be more than that rate. No doubt the slow moving upper trough over the gulf will aid in the instability through the day as storms are expected to slow intensify. A lack of solar insolation may slow things down somewhat when compared to yesterday but some areas will no doubt clear up a bit during the day.

 

There is a slight chance that a funnel cloud or possibly a water spout could form in the vicinity of the upper low over eastern gulf waters today and possibly into tomorrow. These should pose little risk to non marine areas but it is possible that they could impact some coastline if they occur. Marine waterspout watches have already been issued, and the funnel cloud sign on the outlook is for that possibility.

 

Thunderstorm Outlook for Today

 

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Thunderstorm Outlook for Tomorrow

 

Mel Lemmon