Day 1 Convective Outlook for Atlantic Canada Valid for June 6, 2018

 

Convective Discussion

 

Nil significant convective weather is expected across Atlantic Canada today. Isolated to scattered shower development is expected over central New Brunswick this afternoon and early this evening. Slight risk of convection this afternoon over southern Nova Scotian waters and late this evening/overnight over southern Newfoundland waters  as a weak low pressure system currently over southwestern Nova Scotian waters will slowly track northeastward throughout the period.

 

Technical Discussion

 

Ridging moving into the region from the northwest, and multiple low pressure systems crossing the southern marine districts of both NS and NL, will generate conditions that are not condusive for the production of severe convection over the provinces today. Capping exists throughout the region and although some dynamic forcings are present, they are not expected to be strong enough to erode the capping inversions. Moisture across the region is also generally low, with the most moisture being confined well south of the Atlantic Provinces and near the Gulf Stream. There is an upper trough that is currently moving through northwestern New Brunswick and is expected to help generate TCU across central and western regions of the province this afternoon. Showers that will develop with the passage of this feature are expected to be generally light with an isolated moderate shower where day time heating and moisture availability is largest.  

 

Regional Impacts

 

Newfoundland and Labrador: Nil sig severe convective weather is expected today.

 

PEI and Nova Scotia: Nil sig severe convective weather is expected today.

 

New Brunswick: Showers associated with the passage of an upper trough are expected to develop this afternoon. No significant convective weather is expected to develop this                afternoon with the passage of the aforementioned feature.

 

Southern Nova Scotia and Southern Newfoudland marine districts: Slight chance of thunderstorms this afternoon associated with the passage of the afforementioned low. Primary regions of potential development are over the southern marine waters with the warmest sea surface temperatures, from Georges Bank to East Scotian Slope. Slight chance of nocturnal thunderstorms associated with the passage of this low over Laurentian fan late this evening and overnight for extreme southern portions of the Southwestern Grand Banks. Should thunderstorms develop, their primary threats would be wind gusts near 35 knots.

 

 

Marshall Hawkins

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