Convective Outlook Valid for Today and Tomorrow

Regional Impacts

 

New Brunswick: Severe thunderstorms possible giving local heavy downpours, strong wind gusts, and small hail this afternoon in central and southern New Brunswick.

 

Labrador: Locally heavy downpours, moderate to strong wind gusts, and hail are possible today and this evening over central and western Labrador.

 

Newfoundland: Isolated embedded thunderstorms giving locally heavy downpours and moderate winds gusts are possible today over western Newfoundland and surrounding marine waters.

 

 

Convective Discussion

 

There are a few areas of interest to keep an eye on today. A strong area of low pressure currently over northern Quebec will move over northern Labrador this evening. Meanwhile, a short wave with a warm front has been moving over the Gulf of St. Lawrence this morning and into western Newfoundland, firing off some embedded thundershowers this morning which may continue into the early afternoon and possibly into the overnight period. Thirdly, the cold front currently over southern Quebec will track through New Brunswick this afternoon and into Newfoundland overnight.   

 

The highest areas of concern are over central/southern New Brunswick and Labrador this afternoon. The upper dynamics are favourable over Labrador as they are within the left exit of an upper jet with ample diffluence and cooling aloft at 500 mb. Precipitable water values are in the high 20s. The main thing holding any cells the develop is the lack of strong wind shear.  There could still be enough energy that some cells could form strong lines with moderate to strong wind gusts and small hail given freezing levels near 12,000 ft.

 

For New Brunswick, there is the potential for severe thunderstorms with some favourable upper dynamics and the cold front being the trigger ahead and along it this afternoon for central and southern areas. There is ample moisture with precipitable water near 50 mm, and 0-6km shear in the low 40s but shear will be decreasing into the afternoon.  The main inhibitor is a current capping inversion seen on the 12Z Caribou sounding at 750mb and some additional warming between 500-700mb. Therefore, daytime heating and any additional low-level moisture will be the key in if this area sees only 500 J/kg CAPE values, or over 1000 J/kg. There is enough clearing over northwestern New Brunswick that cloud cover does not look to be an issue. Should this cap break, some stronger squall lines could develop with heavy rain (25+mm/h) and strong winds ( 70-90 km/h) as well as a slight possibility of supercells ahead of the front. Small hail (<2 cm) is also possible but freezing levels near 15,000ft should prevent any large hail from developing.

 

Thunderstorm Outlook for Day 1

 

 

 

Thunderstorm Outlook for Day 2

 

Convective Outlook Valid for Today and Tomorrow

Thunderstorm Outlook for Day 1

 

Regional Impacts

New Brunswick: Scattered thundershowers beginning by early to mid afternoon, with some heavy downpours and gusty winds.

Labrador: Isolated to scattered thundershowers with some gusty winds and brief heavy showers.

 

 

Convective Discussion

 

There’s a deep upper low over northern Hudson Bay , with a deep upper trough extending southeast over western Labrador into the eastern Gulf of St. Lawrence. There is also a deep upper thermal trough west of Labrador. Weak to moderate 250 and 500 jets have Right Exits near and north of the Gaspe Peninsula and all of this is slowly moving east. There is a reasonable chance for near severe thunderstorms for New Brunswick, with a slight chance for severe. Upper dynamic support is limited to the extreme north of the province, but there is healthy shear near 40 kts, moderate PWAT around 30-35 mm,  but with no really significant amounts from the surface to 700 mb, then with some drying. The main mechanism will be daytime heating, and some extra moisture from low stratus over New Brunswick, and a surface trough from western Labrador to just northwest of New Brunswick along the St. Lawrence as a possible organising feature. The main impacts will be locally heavy downpours and some gusty winds. Significant hail is unlikely, with freezing levels near 115 to 145 hft for Caribou and Gray.

 

For Labrador TCus have started, associated with the trough over western Labrador, and some thundershowers should start soon. This and daytime heating are the triggers and organising features. PWAT is 15 mm near YYR and 30 near YWK,  And shear is near 15 kts east and 25 west. The stability will inhibit things somewhat with a weak inversion from near 800 mb upwards. All this suggests the western cells will be a bit more  intense. Maximum CAPEs should be near 250 J/kg. So the major impacts are some intense but brief showers, some gusty winds, and a slight chance for hail.

 

 

 

Thunderstorm Outlook for Day 2

For day two a deep upper ridge starts to move in, and upper  dynamic support is minimal. However weak low level troughs approach western Labrador and the western Maritimes, and there’s a chance for some thundershowers, with a bit more support for New Brunswick with higher moisture, shear, and potential moderate CAPE.

Convective Outlook Valid for Today and Tomorrow

Regional Impacts

 

Southern Grand Banks may see some elevated thundershowers today and overnight. No other regional impacts are expected.

 

Convective Discussion

 

An upper-level low is slowly tracking over the southern marine district and will stall over the Grand Banks today and tomorrow. Most convection associated with the low is now south of the Maritimes marine waters, however, a strong southerly push over the eastern Grand Banks and upper level jet over the area will help lift. The highest risk for embedded convection will be in the overnight hours into Friday morning, when cloud top cooling will also help to enhance the destabilisation aloft.

 

Thunderstorm Outlook for Day 1

 

 

 

Thunderstorm Outlook for Day 2

 

A large trough will approach Atlantic Canada from central/northern Quebec on Friday and a secondary trough further south over southern Quebec. At this time, the dynamics appear more favourable further west over Quebec as the air aloft over New Brunswick remains too warm and would need a good amount of surface based heating in order to break the cap. Showers are expected to move into western New Brunswick in the mid afternoon so cloudiness out ahead in the morning could be key factor for anything getting going other than showers. Low risk has been added for now.

 

 

Convective Outlook Valid for Today and Tomorrow

Regional Impacts

 

Eastern Nova Scotia, southeastern Newfoundland, and the southern marine district will see locally high rainfall amounts with embedded thunderstorms possible mainly over the southern marine waters as an upper level features slowly moves eastward south of Nova Scotia today.

 

Convective Discussion

 

An upper-level low south of Nova Scotia will move eastward toward the Grand Banks today and stall over the area into Friday. For today, the primary threats for embedded convection will remain offshore near and ahead of the low centre, but there could be some enhancement this afternoon over eastern parts of Nova Scotia including Cape Breton as the low drifts further east. This system had a history of dropping high rainfall amounts over parts of southwestern Nova Scotia with precipitable water values of near 40 mm were and this may be the case today over eastern portions.

 

Thunderstorm Outlook for Day 1

 

 

Thunderstorm Outlook for Day 2

 

The upper-level low will stall over the southeastern Grand Banks where some embedded convection may develop in the overnight hours into Friday morning.

 

Convective Outlook Valid for Today and Tomorrow

Regional Impacts

 

Nova Scotia.. A stationary area of thunderstorm development over southwest Nova Scotia could produce locally heavy rainfall amounts of 20 to 30mm.

 

New Brunswick.. A low probability of isolated thundershowers late this afternoon or this evening.

 

Convective Discussion

 

Thunderstorm development is expected to continue ahead of and near an upper low that is slowly progressing towards the Maritimes. Most of the convection will be triggered aloft but daytime heating could contribute to increased updraft strength this afternoon. There is some indication that a quasi-stationary feature could set up possible giving heavy rainfall amounts to some parts of southwest Nova Scotia.

 

Thunderstorm Outlook for Day 1

 

 

Thunderstorm Outlook for Day 2