Convective Outlook Valid for August 22 2019

Convective Discussion.

 

A frontal wave currently over the lower St Lawrence will continue to move eastward today under a very strong upper level wind flow. The surface cold front has moved south of the St Lawrence river this morning and dry/stable air is now found west of it. The low cloud continue to dissipate over the Maritimes as the cold front approaches. Ahead of the front, the air mass remains marginally unstable and with the some limited daytime heating of the surface scattered thunderstorms will develop once a warm layer in the low to mid levels becomes eroded. Current radar indicates early development over the mountains of the Eastern Townships and Maine Highlands. These storms will  propagate eastward as the front pushes through NB later in the day.  

 

Regional Impacts.

 

Newfoundland&Labrador: Isolated non-severe thunderstorms.

 

Nova Scotia: Risk of a thunderstorm over central, northern and eastern regions.

 

New Brunswick: Scattered thunderstorms developing west of the region moving east. The main threat is very high wind gusts.

 

Prince Edward Island: Risk of thunderstorms late today.

 

 

Jean-Marc

 

Convective Outlook Valid for August 21 2019

Convective Discussion.

 

A frontal wave over southern Quebec will reach the Maritimes tonight. Ahead of this feature, an area of showers currently over the lower St Lawrence will reach northwestern NB this afternoon. This morning’s soundings from the area are showing limited potential energy so any daytime thunderstorms activity will be limited to Maine and Quebec.

 

This evening and overnight the air mass will become much more humid and unstable as a trough pushes through. Some residual convective features from the west will also spread across the Maritimes, especially across western NS where downpours are likely.

 

Regional Impacts.

 

Newfoundland: none.

 

Labrador: Scattered showers only.

 

Nova Scotia: Dry today, Numerous thundershowers tonight with downpours likely over western sections.

 

New Brunswick: Scattered showers in the northwest today, risk of thundershowers across the province tonight.

Prince Edward Island: Dry today, risk of thundershowers tonight.

 

 

Jean-Marc

 

Convective Outlook Valid for August 20th, 2019

Convective Discussion.

 

A few areas of convective activity to note mainly over Newfoundland and Labrador today as a quasi-stationary low over northern Quebec with a trough extending through Labrador, Newfoundland, and eastern Nova Scotia today.

 

The air mass within the trough extending from Newfoundland towards eastern Nova Scotia is quite moist in the low levels with dew points remaining near 20C. Surface temperatures are already near the daytime highs expected over western areas of Newfoundland despite the current cloud cover. The question will be how much additional surface based heating there will be should the cloud break up more. The inhibitor for this afternoon is a slight warming expected in the mid levels which could cut the potential energy of any convection that develops. Despite this, any showers already on the go and what could develop this afternoon will produce locally heavy downpours given the high pecipitable water values in the area as well as strong wind gusts. There should only be a slight risk of a thundershower over eastern Nova Scotia early this afternoon as the trough is currently moving over the area and some coastal convergence could provide further lift. Dew points will still remain high for a few hours after this trough moves through as the more pronounced change in humidity is still further west over New Brunswick.

 

For central Labrador, the area remains under an unstable westerly flow.  A 500mb cold pool lies over central Quebec to central Labrador providing sufficient lift given daytime temperatures in the upper teens. Air mass type thunderstorms are expected but some further organization is possible given convergence near the trough and low pressure centre that is expected to form over eastern Labrador this evening and push off into the Labrador Sea tomorrow morning.  Precipitable water remains moderately high so convection this afternoon will likely produce some heavy downpours. Hail is also a risk with freezing levels dropping below 10,000ft.

 

Regional Impacts.

 

Newfoundland: Locally heavy downpours and strong wind gusts.

 

Labrador: Locally heavy downpours, strong wind gusts, and small hail.

 

Nova Scotia: An isolated thundershower over eastern sections this afternoon.

 

New Brunswick and Prince Edward Island: nil

 

 

Roberta McArthur

 

Convective Outlook Valid for August 19th, 2019

Convective Discussion.

 

It should be active afternoon and evening for much of western New Brunswick and into the rest of the Maritimes and Labrador overnight as a short wave trough extending from a low pressure system over Hudson Bay tracks through the region.

A warm front has been producing some heavy showers and occasional embedded thundershowers this morning over Maine which will continue into New Brunswick and the Bay of Fundy but will also continue to fizzle into the afternoon. The cold front is not far behind over southern Quebec and will begin to track through New Brunswick late this afternoon and into tomorrow morning over Nova Scotia and Newfoundland.

 

For New Brunswick behind the warm front this morning, there should be some clearing in the warm sector ahead of the approaching cold front this afternoon. Low-level moisture is already quite high in the region with dew points 18-20C and precipitable water values reaching 40 mm. Surface based convection is expected to begin this afternoon as temperatures reach the mid 20s given sufficient clearing. Upper divergence and further cooling aloft will provide further instability into the afternoon with CAPE values nearing 1000 J/kg over northwestern New Brunswick. Low to mid-level shear is also expected to increase to 30-40KT by the evening. These ingredients will all help to initiate and potentially sustain severe thunderstorms into the evening. Multicells may organize into bow lines or supercells ahead of the cold front. The main threat will be heavy downpours, strong wind gusts, and small hail. The potential for a tornado cannot be ruled out given the amount of low-level shear mainly over northwestern New Brunswick as well.  

 

Over Labrador, there risk of non-severe thunderstorms over central and western areas as late this afternoon and evening as the trough from the low pressure centre over Hudson Bay progresses northeastward. Locally heavy downpours are possible.

 

Regional Impacts.

 

New Brunswick: Strong wind gusts which may approach 90 km/h, locally heavy downpours(25+mm), and small hail (1-2cm.

 

Nova Scotia and Prince Edward Island: Locally heavy downpours and strong wind gusts.

 

Labrador: Locally heavy downpours

 

Newfoundland: Nil

 

 

Roberta McArthur

 

Convective Outlook Valid for August 18, 2019

Convective Discussion.

Early morning convection across southwestern NB has weakened and will continue to weaken this morning. There were a couple embedded TSRA, but increasing stability will negate any more CBs. The only area where cells are possible are across ERN LAB. Adjusting the surface temp to around 26 from YYR gives close to 500 J/kg. A surface trough will act as a trigger this afternoon. Sat pix shows some decent clearing across the region as well. Precipitable water is fairly low, but freezing levels are low and the shear is modest at around 35 knots or so. Expect some gusty winds and possible small hail in a couple of the cells. Elsewhere no convection is expected in Atlantic Canada.

Regional Impacts.

Labrador: scattered TS this afternoon giving gusty winds and possible small hail for ERN regions.

Nova Scotia/New Brunswick/PEI/Newfoundland: nil.

Jeremy