Convective Outlook Valid for Today and Tomorrow

Regional Impacts

Southeastern Labrador could experience strong thunderstorms this afternoon - the main threat is damaging wind gust, brief downpours and small hail – into the evening.

 

Convective Discussion

This morning, a frontal wave was located south of Newfoundland. The elongated front has an history of producing locally heavy rain as far back as NB (reports of rainfall rates of 20-40 mm). Earlier lightning activity has faded during the past two hours. This feature will continue to move eastward – out of the region - throughout the afternoon.

The main are of focus for the afternoon is Labrador where an upper cold low prevails. The cold pool would be sufficient to trigger isolated thunderstorms, but this likelihood will be enhanced by an approaching vorticity rotating around the low. The moisture available in this airmass is not tremendous, but the energy available is high enough to anticipated the development of fairly robust eastward moving storms capable of producing small hail, damaging wind gusts and localised downpours.

 

 

Thunderstorm Outlook for Day 1

 

 

 

Thunderstorm Outlook for Day 2

 

 

Convective Outlook Valid for Today and Tomorrow

Regional Impacts

Strong clusters of thunderstorms could produce localized heavy downpours early this afternoon over southwestern Nova Scotia.

Later this afternoon, thunderstorms formation over central and southern Maine could spread robust clusters over southwestern New Brunswick, the main threat would be brief heavy rain and damaging wind gusts.

 

Convective Discussion

 

An upper trough along with a weak cyclonic upper jet over northern Quebec could trigger an isolated thunderstorm over western Lab, in the east Goose is showing stability in the mid-levels so convection will be limited to fair weather cumulus. For the Maritimes, two distinct air mass present different threat. For Nova Scotia a surface front extends from the New England coast to Northumberland Strait, a southwesterly low-level jet is feeding moisture over the area with moderate to heavy rain expected at times. For New Brunswick, a surface feature to the west will provide the forcing necessary for thunderstorm initiation over the Maine Highlands. A 100kt upper level jet could help sustain these individual storms long enough for them to propagate eastward into western NB.  Although the main threat with these storms would be brief downpours and damaging wind gusts - none of the severity indicators are particularly high at this point.

 

Thunderstorm Outlook for Day 1

 

 

 

Thunderstorm Outlook for Day 2

 

Convective Outlook Valid for Today and Tomorrow

Regional Impacts

 

NS/NB/PEI: None

Nfld & Labrador:  A risk for offshore waters.

 

Convective Discussion

 

A weakening cold front is moving across Newfoundland today.  There is a very small chance of thundershowers this afternoon over eastern Newfoundland but should be confined to offshore waters.  

 

 

Thunderstorm Outlook for Day 1

 

 

 

Thunderstorm Outlook for Day 2

 

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.