Convective Discussion
Technical Discussion
Regional impacts
Monday, June 11, 2018
Day 1 Convective Outlook for Atlantic Canada Valid for June 11th, 2018
Friday, June 8, 2018
Day 1 Convective Outlook for Atlantic Canada Valid for June 8th, 2018
Convective Discussion
This is a very low probability of non-severe thunderstorms over southern New Brunswick and Western PEI late this afternoon ahead of an approaching cold front. For Eastern PEI and Northern Nova Scotia this risk will continue into this evening. There is a very slight chance of weak embedded thunderstorms with enhanced rainfall amounts possible should they develop.
Technical Discussion
Overall the amount of low level moisture and instability is not favorable for the development of thunderstorms with most unstable CAPE values < 250 J/kg. However with the presence of the approaching cold front stretching from Labrador down into New Brunswick as a trigger and an approaching cold trough aloft there is a slight risk that thunderstorms may develop. This is risk may also be enhanced slightly over areas of higher terrain and max daytime heating later today.
Regional Impacts
New Brunswick: Showers and risk of weaker thunderstorms over southern New Brunswick beginning late this afternoon. No significant impacts expected.
Nova Scotia: There is a slight risk of weak thunderstorms late this afternoon and this evening over parts of northern Nova Scotia. No significant impacts expected.
Prince Edward Island: There is a slight risk of weak thunderstorms late this afternoon and this evening. No significant impacts expected.
Newfoundland and Labrador: There is a slight risk of weak thunderstorms late this afternoon for southern Labrador and this afternoon and evening for western Newfoundland. No significant impacts expected.
Mel Lemmon
Thursday, June 7, 2018
Day 1 Convective Outlook for Atlantic Canada Valid for June 7, 2018
Convective Discussion
There is a risk for non-severe thundershowers over northern New Brunswick late this afternoon into the evening and overnight with an approaching low pressure system over central Quebec tracking eastward today. Elsewhere no significant convection is expected with a ridge of high pressure stretching from Labrador to Nova Scotia keeping conditions dry.
Technical Discussion
The warm front in association with the low pressure system over Quebec has pushed north of New Brunswick. The ingredients necessary to initiate and maintain convection this late this afternoon over northern New Brunswick should be present. In the upper levels, there is an approaching 80KT 250mb jet and northern New Brunswick lies in the favourable left exit region. The 500mb level has increasing diffluence, slightly cooling temperatures, as well as increasing 700 and 850mb warming will help to destabilize the air mass. A trough within the warm sector is also expected to push eastward over Northern New Brunswick tonight to kick start the convection. The biggest inhibitor are the current relatively dry low levels and moist upper levels. Upstream precipital water values are in the range of 15-20mm. There is also widespread cloud cover currently from Quebec into western New Brunswick which may delay convective initiation if convective temperatures are not reached. If they do, only CAPE values maxed near 500 J/kg will be reached. Freezing levels are low so there is the risk of small hail.
Regional Impacts
New Brunswick: Showers and risk of thundershowers over northern New Brunswick beginning late this afternoon and may continue into the early overnight hours. Some local heavy downpours, gusts to 50 km/hr, and small hail (<2cm) are possible.
Nova Scotia: None
Prince Edward Island: None
Newfounland and Labrador: None
Roberta McArthur
Wednesday, June 6, 2018
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
Tuesday, June 5, 2018
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
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