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

 

 

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

 

Convective Discussion

 

A warm and humid air mass will approach New Brunswick on Friday ahead of a low pressure system moving eastward over Quebec. The atmosphere will be conducive for the development of thunderstorms in the afternoon given increasing moisture in the low levels, moderate low level wind shear and high maximum temperatures. These ingredients along with an approaching cold front will help de-stabilize the air mass and initiate afternoon showers and potential thundershowers over northwestern New Brunswick beginning in the afternoon and spread southeastward into the evening.

 

Regional Impacts

 

The main threat with the potential thundershowers will be local heavy downpours and some moderate gusts.

 

 

Roberta McArthur