Convective Outlook for Atlantic Canada Valid for June 14th, 2018

Convective Discussion

Isolated thundershowers continue across southern New Brunswick, northern/eastern Nova Scotia, and southern marine waters today. This activity will reach the Grand Banks tonight.

Technical Discussion

An upper low over the Eastern Townships this morning is supporting a surface low pressure system over southern Maine. A large area of rain ahead of these features extends from the Saguenay across the Maritimes to just south of Newfoundland. Based on the 12z sounding from Gray, Me, the instability in the cold pool is sufficient to supports elevated CB’s based around 10,000ft with tops above 35,000. Latest radar echo top products is a small cluster of thundershowers with these characteristics just north of the Minas Basin. Some of the soundings this morning showed precipitable water of 25-35mm. Widespread rainfall totals of 10-15mm have been reported , with peak hourly amounts of 11.5mm reported at YCX earlier this morning.

Regional impacts

NS/NB/NL/PEI/LAB: Brief localized mod-heavy rain..

Jean-Marc

Day 1 Convective Outlook for Atlantic Canada Valid for June 12th, 2018

Convective Discussion

No convective weather expected across Atlantic Canada today.

Technical Discussion

A low pressure system over western Labrador will track southeastward today. A trailing cold front may give thundershowers this afternoon or evening over regions near and north of the Gaspe Peninsula. CU development is expected over portions of eastern NFLD and LAB today but the airmass is dry so just a few showers will be a result. Synoptic rain and snow is expected over western LAB closer to the low.

Regional impacts

NS/NB/NL/PEI/LAB: Nil.

Andy

Day 1 Convective Outlook for Atlantic Canada Valid for June 11th, 2018

Convective Discussion

No significant weather expected across ATL CAN.

Technical Discussion

Upper level trough remains over the region today with cold, dry air in the low levels. Strong capping associated with an approaching area of high pressure is limiting the cloud development to CU and SC. There is a zero percent chance of TS activity today.

Regional impacts

NS/NB/NL/PEI/LAB: Nil.

Andy

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

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