Day 1 Convective Outlook for Atlantic Canada Valid for June 5, 2018

Convective Discussion

 

Nil significant convective weather is expected across Atlantic Canada in the short term.  Isolated thunderstorms / thundershowers are expected to continue across parts of the southern Nova Scotia marine district today, and possibly over the eastern Nova Scotian and southern Newfoundland marine district overnight.

 

Technical Discussion

 

Multiple capping inversions remain across the region, and only thin regions of potential instability exist across the majority of actual sounding sites throughout Atlantic Canada. To overcome these various caps, significantly more moisture and daytime heating is required than is currently forecast; therefore no significant convective weather is expected across any of the provinces today.

 

The primary threat area to produce severe convective weather for the marine districts stems from the passage of a frontal wave and associated low pressure system that is forecast to continue to move northeastward, crossing from the southern NS marine district to the southern NL marine district. Current thunderstorm activity associated with this wave is producing isolated cells along the border of Sable and East Scotian Slope with cloud tops near 37,000ft (radar observed, consistent with RDPS NWP), surface wind observations through SAR/ASCAT have not been able to produce a measurement of this activity as of the time of this bulletin. Isolated cells associated with this wave are expected to continue today, and may intensify slightly overnight as cloud top cooling ahead of the warm front begins to play more of a role throughout the nocturnal hours.

 

Although there is a capping inversion across the marine district that would inhibit significant surface based convection, a strong low level jet is present below this inversion. The presence of this strong LLJ along with an unstable lower boundary layer may produce gusts near 45 knots should a cell form over the most unstable regions associated with the warmest Gulf-Stream waters for the southern Nova Scotia marine district. Given the transition to cooler water as this system moves into the Newfoundland marine area of responsibility, the persistance of thunderstorms would rely upon continual Warm Air Advection (WAA) and cloud top cooling (CTC) – the marine inversion would remain strong and likely prevent significant gusts from reaching the surface.

 

Overnight a second low pressure system may produce nocturnal thunderstorm activity over the sotuhwestern slope waters of Nova Scotia as positive voriticity advection along with WAA and CTC will be present over relatively warm waters. It is possible that thunderstorm activity that is expected to occur over eastern New England this afternoon may persist as this low moves off shore and eventually crosses into the south western NS marine district. Threats with these cells would be primarily wind gusts exceeding 35 knots.

 

Regional Impacts

 

Newfoundland and Labrador:  No significant convective weather expected.

 

New Brunswick, Pei, and Nova Scotia: No significant convective weather expected.

 

Southern Nova Scotia and Southern Newfoundland Marine districts: Risk of thunderstorms activity throughout the remainder of today for NS and into tonight southern NFLD Marine (21 UTC onward). Gusts today for NS/NL may peak near 45 knots – which is not entirely significant compared to the currently forecasted gale-force conditions from either issuing office. Squall watches are not expected to be required at this time.

 

Marshall Hawkins

 

 

Day 1 Convective Outlook for Atlantic Canada Valid June 4th, 2018

Convective Discussion

A ridge of high pressure entrenched over much of Atlantic Canada is expected to inhibit any severe convective weather for the immediate short term. Overnight tonight, a low south of Cape Cod is expected to migrate northeastward and track south of Nova Scotia – as it does so there is a slight risk for convection over southwestern Nova Scotia and across the marine regions south of the province and in the vicinity of the low centre.

Technical Discussion

An exceptionally dry air mass (throughout the majority of the column) stretching from western and central Labrador to Nova Scotia will inhibit the development of any severe convective weather through max daytime heating today and into this evening for all of Atlantic Canada. Although some weak thundershower activity has been associated with the approaching trough over New England and Southern Ontario (Ottawa River Valley) no significant convective weather is expected to move in over the Maritimes with the approach of this feature due in part to the aforementioned dry air mass. There is however a slight risk for nocturnal convective activity for Nova Scotia (and NS Marine) as  a developing low pressure system currently south of Cape Cod is expected to track northeastward throughout the period and upper level vorticity combined with a thermal ridge (and corresponding moisture axis as well as cloud top cooling) are expected to produce conditions favorable for isolated elevated nocturnal convection.

Newfoundland and coastal Labrador remain in a synoptic flow that is not conducive to the development of severe convective weather.

Regional Impacts


Newfoundland & Labrador: None via convective severe weather.


PEI: None via convective severe weather


New Brunswick: Possible moderate showers via ACC associated with the passage of the trough near 03 UTC and onward...otherwise, nil convective severe weather.


Nova Scotia & Nova Scotia Marine district: Risk of isolated nocturnal thundershowers/thunderstorms after 03 UTC. Should one develop, the primary risk (for the strongest cells) would be gale force wind gusts near 40 knots over southern waters where water temperatures are warmest.

Marshall Hawkins

Day 1 Convective Outlook for Atlantic Canada Valid for June 3, 2018

Convective Discussion

Technical Discussion

There is a low southeast of the Avalon slowly moving away to the east. Further west is an upper level jet moving in ahead of ridging, and the left exit of the jet may give some upper lift. While there is no chance of surface forcing with a strong inversion and cold water, above 850 mb stability is less than moist adiabatic.

Regional Impacts

Minimal impacts over the southern Grand Banks, mostly isolated thundershowers possible near and west of the low center.

Doug Mercer

Day 1 Convective Outlook for Atlantic Canada Valid for June 2, 2018

Convective Discussion

 

Technical Discussion

A trough of low pressure could initiate some mid level convection over the contoured area today.  The upper levels are quite warm so if convection does get initiated, CAPE values of up to 200 J/kg could be realised but higher CAPE values are not likely so severe thunderstorms are not expected.

 

Regional Impacts

None

 

Barrie MacKinnon

 

Day 1 Convective Outlook for Atlantic Canada Valid for June 1, 2018

 

Convective Discussion

 

A warm and increasingly humid air mass is approaching New Brunswick today ahead of a low pressure system over Labrador with a cold front extending into central Quebec. The atmosphere will be conducive for the development of thunderstorms in the afternoon given falling 500mb heights, increasing moisture in the low levels and high maximum temperatures. These ingredients along with the approaching cold front will help de-stabilize the air mass and initiate showers and thundershowers over northwestern New Brunswick beginning in the afternoon and spread southeastward into the evening. Due to the high precipital water content in this air mass and not much wind aloft, showers that develop will move slow and local heavy downpours are possible. The risk of thundershowers may continue into Nova Scotia overnight.

 

Regional Impacts

 

The main threat with the thundershowers will be locally heavy downpours (20-40mm possible).

 

 

Roberta McArthur