Convective Outlook Valid for July 6, 2019

Convective Discussion

Non-severe thundershowers possible for much of Atlantic Canada, with possibly near severe impacts for northern and western Labrador this evening, for central New Brunswick for this afternoon possibly into this evening, and for northwestern Newfoundland.

All of this is related to an occluded low south of Ungava Bay, and a frontal system extending southwest from Labrador southwest into Maine. This is giving some dynamic support, mainly for New Brunswick for Today and Labrador for tonight. There’s some convection over Labrador ahead of the occluded low, and some insolation over the west. Dewpoints are a bit on the low side (10-15 C), but PWAT is in the 30 mm range, which isn’t bad. The upper jet approaching has some PVA, and when it sinks southeast there will be some enhanced lift from the Left Exit to the northwest. Shear is on the high side at 50+ kts, which isn’t likely to drop with the approaching jet, and will reduce local rainfall amounts, and may be too high relative to the CAPE to produce supercells.. The basic idea is that convection will persist into tonight.

For New Brunswick. Ingredients are healthy for convection, which may near severe status. Currently there is scattered convection in the clearer air ahead of the front, which may argue for more moderate cells. Moisture is good as the surface with 20C dewpoints, and at 850 mb  near 14C dewpoints. PWAT is near 50 mm. Instability is okay with CAPEs currently near 3-400 J/kg, and possibly a bit higher this afternoon. Later this afternoon CAPEs may near 500-1000 J/kg, which may be enough to near severe. The shear is currently near 30 kts, which is marginal for severe conditions,  but will increase a little this afternoon.

For Newfoundland the approaching front will act a bit like the conditions for New Brunswick, with marginal shear (30-40 kts) , probably lower CAPEs, slightly lower dewponts (near 16 C), and PWAT near 35 mm. Because of the timing and orientation of the trough, things should max out later in the afternoon roughly near the Deer Lake region.

Regional Impacts

Labrador: Non-severe thundershowers for most areas developing this afternoon with high intensity beginning this evening, with stronger cells north of the Labrador Highway and west of the mid Labrador coast. Impacts will be mainly local heavy downpours and some gusty winds. There may also be some hail further north.

Newfoundland: Non-severe thundershowers beginning early in the afternoon. Impacts will be local heavy downpours, followed by gusty winds. The Deer Lake region and points north on the Great Northern Peninsula should have more significant impacts.

Maritimes: Non-severe thundershowers today for New Brunswick and a chance for Prince Edward Island, with the most significant impacts for the southern half of New Brunswick  except for the Fundy Coast. For this evening a risk of thundershowers Nova Scotia. Impacts will be local heavy downpours and gusty winds.

Marine waters: Embedded convection possible for all Maritimes waters today and tonight, with stronger cells over southernmost waters. Also a slight chance near the Labrador Coast, and the Northeast Coast of Newfoundland.

Doug Mercer

Convective Outlook Valid for July 5, 2019

Convective Discussion

Near severe thundershowers  possible for  northern New Brunswick, with non-severe thundershowers possible for much of the Maritimes. Thundershowers possible for western Labrador and the Maritimes.

Maritimes: These will be mostly air mass driven by daytime heating up to the low thirties and dew points near 15-20 C . A deep ridge will move though New Brunswick this afternoon and over eastern Nova Scotia by this evening, having generally sunny conditions. CAPEs near or possibly exceeding  500 J/kg range are reasonable for the Maritimes provinces, with New Brunswick possibly in the 500-1000 J/kg range, and possibly higher central and north. The highest risk are for heavy downpours and high wind gusts. The main factors against these cells developing is a lack of moisture aloft, as well as a lack of upper support. 0-6 km shear is near 30 kts, and will diminish a bit this afternoon. Freezing levels near 13 to 15 thousand feet make significant hail unlikely.

Labrador: For western Labrador  there are two factors that may spawn some weak cells this afternoon, that may become healthier into early this evening. . Near or just east of Churchill falls there is a  north-south trough with some sunny breaks to the west. Farther west there is a weak diffluent upper jet approaching from Quebec.  These, combined with daytime heating may produce some cells with CAPEs up to 500 J/kg, with PWAT near 33 mm, and dew points near 14 C in the west. Wind shear is near 25 kts and will increase from the west into this evening to near 35-40 kts.

Regional Impacts

New Brunswick: : Near severe thundershowers possible this afternoon into this evening with heavy downpours and gusty winds possible.  Highest risk for severe in the north this afternoon.

Nova Scotia: Non-severe thundershowers possible this afternoon into this evening with heavy downpours and gusty winds possible.

Prince Edward Island: Non-severe thundershowers possible this afternoon with gusty winds and occasional heavy downpours.

Labrador: Non-severe thundershowers giving occasional downpours. A slight chance for small hail.

Newfoundland: None

Doug Mercer

Convective Outlook for Atlantic Canada valid for July 4th, 2019

Convective Discussion

 

Thunderstorms expected over eastern New Brunswick and parts of eastern Nova Scotia as well as western Labrador today.

 

The thunderstorms over the Maritimes will be primarily thermodynamically driven.  Lots of solar insolation today combined with good low level moisture will generate moderate CAPE values of around 500 J/kg however the lack of a triggering mechanism should restrain convective development to coastal areas where it will be influenced by a sea breeze and coastal convergence which should act as the kicker.  If thunderstorms develop along the coast, they will likely be slow moving so heavy local downpours will be the main threat.  Looking at satellite this morning, there seems to be a lot of forest fire smoke in the upper atmosphere.  This could impede convection as it will reduce solar insolation. 

For western Labrador, good low level moisture and solar insolation combined with cool temperatures aloft will bring CAPE values of around 500 J/kg.  There is a small possibility of severe thunderstorms being initiated; however, wind shear is quite insignificant, therefore thunderstorms cell will have difficulty maintaining themselves.

 

Regional Impacts

 

New Brunswick

 

Slow moving thunderstorms along the coast which could bring local heavy downpours.  Small hail and moderate winds also possible.

 

Nova Scotia

Slow moving thunderstorms which could bring local heavy downpours.  Small hail and moderate winds also possible.

 

PEI

None

 

Newfoundland & Labrador

For western Labrador,  local heavy downpours and moderate winds with a small chance of cells producing damaging winds. No impacts elsewhere.

 

 

Barrie MacKinnon

 

Convective Outlook for Atlantic Canada valid for July 3rd, 2019

Convective Discussion

 

Risk of thundershowers over western New Brunswick this afternoon and early this evening with no convective activity expected elsewhere.

 

Clearing skies over western New Brunswick will increase solar insolation which may be enough to trigger a few non severe thundershowers.  An approaching ridge  from the west brings subsidence to the area, so any convection that could get triggered should be  moderated due to the mid level stability.  Anywhere from 100 to 500 J/Kg can be expected over the area but, again, positive buoyancy should be limited to mid levels which should limit CB development.

 

Regional Impacts

 

New Brunswick

 

Scattered thundershowers possible over western NB but severe thunderstorms not expected.

 

Nova Scotia

None

 

PEI

None

 

Newfoundland & Labrador

None

 

 

Barrie MacKinnon

 

Convective Outlook for Atlantic Canada Valid for July 2nd, 2019

Convective Discussion

 

The main area of focus will be over Maine with surface based convection having already begun, this convection will spill into New Brunswick this afternoon. Overall dynamics for severe thunderstorms are not overly favorable however there weak surface trough with moderate amount of CAPE > 1000J/kg and high moisture. The main concern will be heavy downpours possibly exceeding 25mm hour and with the low freezing levels 2-3 cm hail is also possible. It is unlikely but some of this convection could move across weather Nova Scotia this evening.

 

Over Newfoundland some embedded CB’s ahead of the surface low pressure system will generate locally heave rainfall amounts.

 

Regional Impacts

 

Nova Scotia

Locally heavy downpours, 15 - 20 mm possible if thunderstorms move into Southwestern parts of the province this evening.

 

New Brunswick

Main concern will be over western regions with heavy downpours 20-25mm and moderate sized hail possible.

 

Newfoundland

Embedded thunderstorms ahead of the surface low could give locally heavier rainfall of 15 – 20mm. Over western Labrador very low topped thunderstorms could develop with some rain and small hail.

 

PEI

None