Day 1 Convective Outlook for Atlantic Canada Valid for August 19, 2018

Convective Discussion

 

No thunderstorms expected over the Atlantic provinces.  

 

 

 

Jean-Marc Couturier

 

Day 1 Convective Outlook for Atlantic Canada Valid for August 18th, 2018

 

Convective Discussion

 

Rainfall warnings are continued for portions of the Maritimes. A large area of heavy precipitation with some embedded thunderstorms extends from Maine to the southwest coast of Newfoundland.

Our autostation at Sussex Corners reported an hourly rate of 30+ mm between 9 and 10 AM with the total for the area now exceeding 80 mm.

The rain will gradually end from west to east during the afternoon and evening.  

 

Technical Discussion

A low pressure system currently over southeastern Maine will travel across Nova Scotia today and exit the province to the south of Cape Breton this evening. A warm front extends from the low eastward to PEI and then to Cape Breton. Radar is detecting a band of heavy showers (and isolated thunderstorms) from the lift provided by the warm front. South of the front the air is very moist, this is highlighted by the Gray and Yarmouth 12z soundings where both are showing precipitable water in excess of 50mm.

While the lightning activity has diminished along the warm front two other areas have now become the focus, in the warm sector a 30kt southwesterly low-level jet is fueling the already moisture-rich airmass resulting in a cluster of thunderstorms over the Baie Ste-Marie area – these storms were moving eastward at about 40 km/h. There is a good chance that these storms could reach the Valley and possibly the Southwest shore early this afternoon, and a slight chance for the rest of the mainland during the rest of the afternoon and early evening. Another area to consider for thunderstorm activity is in the vicinity of the low where a few strikes were detected during the morning.

Regional Impacts.

 

Southeastern NB and Northern and Eastern NS including Cape Breton: rain heavy at times with localized amounts of 50 to 100 mm

Rest of NS: Scattered thundershowers with brief heavier showers giving amounts of 20-40 mm.

 

 

 

 

Jean-Marc Couturier

 

Day 1 Convective Outlook for Atlantic Canada Valid for August 17th 2018

Convective Discussion

 

No Thunderstorms are expected today for the Atlantic Provinces as a sharp change in the airmass with cooler temperatures and lower dewpoints across the region.

 

Regional Impacts

 

Non expected.

 

Mel Lemmon

 

Day 1 Convective Outlook for Atlantic Canada Valid for August 16th, 2018

 

Convective Discussion

 

Convective activity is expected to be confined to the southern Maritimes and southern Newfoundland today. Elsewhere the passage of a cold front mitigates convection for today. The primary threat zone is Nova Scotia from Halifax east. Heavy downpours of rain are the most likely impact. However, strong wind gusts less than 90 km/h and small hail are also possible.

 

Another area to watch is southern Newfoundland where heavy rain is a concern. There is an area of heavy rain and  t-shwrs offshore heading toward the Avalon and Burin Peninsulas that will arrive early this afternoon. Heavy showers and tshwrs will persist into the evening.

 

Technical Discussion

There is an approaching mid level trough and associated cooling aloft that will destabilize the column this afternoon and this evening over the threat area. There is 30 knots of unidirectional shear over the threat area. The 250 mb winds are around 50 knots over the threat area. CAPEs are in the 600-900J/kg range once initiation occurs.

Regional Impacts.

 

Srn NS and srn NB.

 

Hatt

 

Day 1 Convective Outlook for Atlantic Canada Valid for August 15th, 2018

 

Convective Discussion

 

Thunderstorms are expected to form ahead of a cold front approaching from Quebec. There is potential for very heavy downpours or rain, strong winds and possible hail over northern New Brunswick this afternoon and to a lesser extent over central New Brunswick early this evening. Elsewhere some thundershower activity is either occurring or possible today in the areas highlighted. Thundershowers over Labrador are giving significant lightning and possibly gusty winds. However, these thundershowers won’t likely be severe.  

 

Technical Discussion

There is a 250 mb Jet of 75 to 90 knots extending from the Gulf of Maine to northern NB to southern Labrador. There is a deep layer thermal ridge extending from Cape Hatteras to Newfoundland. The associated low level Jet is 20 to 30 knots. The primary triggers are sunshine and the cold front over southern Quebec. Cape values are over 1000 J/kg over the primary threat area. However, there is a cap at 750 – 800 mb that needs to broken before significant thunderstorms can form. Rainfall rates over northern NB could exceed 25mm in an hour due to the fact the airmass is very moist and steering flow is moderate around 20 to 25 knots. There could also be some training of cells due to unidirectional flow from the sfc to 500 mb.

Regional Impacts.

 

Primarily NB, but also Lab.

 

Hatt