Convective Outlook Valid for Today and Tomorrow

Regional Impacts

Risk of  thunderstorms over Northern and Western NB this afternoon, main threat is gusty winds and brief downpours.

Some thunderstorm activity is expected over central Quebec this afternoon and evening, some of these storms may propagate to western Labrador late evening and after midnight

Convective Discussion

This morning, an upper ridge with stable dry conditions prevails over NF, while a cold trough extends from an upper low south of James Bay to southern Quebec. The area with the highest potential for convection is central and southern Quebec and northern Maine. Convective initiation should be fairly easy to attain given the buoyancy of this airmass. Using the most recent Maniwaki sounding, mean layer energy should easily reach 750-1000 J/kg - and with deep layer shear values of about 25kt – this will be adequate to sustain more robust isolated storm cells. Behind the remnants of Isaias, there is a marked drop in moisture content, so the main threat with these storms would be moderate to strong wind gusts.

Thunderstorm Outlook for Day 1

 

Thunderstorm Outlook for Day 2

Convective Outlook Valid for Today and Tomorrow

Regional Impacts

Chance of an afternoon thunderstorm – producing brief downpour and moderate wind gusts - over southern NF.

Convective Discussion

Very moist airmass prevails over NF this morning with a fair amount of potential energy, however mid-level lapse rate continue to be unfavorable for the development of deep convection. The area to focus would be over the southern third of the island where sunshine could help boost surface temperatures to values required for convective initiation, at this point the likelihood remains very low. Having said that, the upper jet (100+kt) may be too strong, shredding any developing towers. Elsewhere across the Atlantic provinces, fair conditions are expected under an upper ridge.

Thunderstorm Outlook for Day 1

Thunderstorm Outlook for Day 2

Convective Outlook Valid for Today and Tomorrow

Regional Impacts

Scattered thunderstorms over central northern and western New Brunswick could produce brief heavy showers and strong wind gusts.

 

Convective Discussion

An approaching cold front and trough currently over southern Quebec will trigger a few thunderstorms this afternoon. Ahead of the front, strong southwesterly flow at all levels will maintain very moist conditions. Low level destabilization during the afternoon will likely lead to some of the storms approaching severe limits – mainly west of our area of responsibility -  however mid-level lapse rates will not be the best over NB.

 

 

Thunderstorm Outlook for Day 1

 

 

Thunderstorm Outlook for Day 2

Convective Outlook Valid for Today and Tomorrow

Regional Impacts

 

NS/NB/PEI/NFLD: None

Labrador:  A risk for western regions with a chance of gusty winds and hail.

 

Convective Discussion

 

A low pressure system will approach western Labrador today. Ahead of the low, daytime heating will allow temperatures to approach 28 degrees. Modifying the upstream sounding at La Grande yields precipital water near 30 mm, cape of 600 J/kg and unidirectional shear of 40 kts. Additionally the freezing level is fairly low at 10,000 feet.  An upper level jet will approach later this afternoon but western Labrador does not look to be in a favourable area of enhanced lift. The low freezing levels and decent cape above -10 C will support hail growth. The dry mid levels will support possible wind gusts.

 

Thunderstorm Outlook for Day 1

 

 

Thunderstorm Outlook for Day 2

 

Convective Outlook Valid for Today and Tomorrow

Thunderstorm Outlook for Day 1

 

Regional Impacts

Newfoundland: scattered non-severe thunderstoms, with a chance for severe southeast towards the Avalon Peninsula. Local heavy downpours, followed by gusty winds and a chance for small hail on the southeast.

Nova Scotia and New Brunswick: non-severe isolated to scattered thunderstorms

 

Convective Discussion

A vertically stacked low over western Newfoundland and the eastern Gulf dominates the convective situation today.  The low is moderately unstable, with some extra support for southeastern Newfoundland with PVA and a left exit from the 500 mb jet a little south of the Avalon. Moisture is okay, with PWAT near 30 mm and surface dewpoints near 17, but there’s not a lot ov water above 850 mb. Weak shear over central and west increased to near 40 kts at YYT at 12Z. Mean layer CAPEs in excess of 500 J/kg are possible in the northeast and central, with a possibility for exceeding 800 J/kg in the southeast. The main threats are for rainfall possibly exceeding 25 mm/h over the Avalon, and possibly over 25 mm over a couple of hours elsewhere, followed by gusty winds, and the possibility of small hail for central and northeast, but less likely over the Avalon, where freezing levels were about 12,700 at YYT, and 10,800 ft at YJT.

 

For the Maritimes, non-severe thndertorms are possible. With near 30 kts of shear, PWAT near 30, weak dunamic forcing and some surface convergence for easter Nova Scotia and southern Cape Breton Island.

 

 

Thunderstorm Outlook for Day 2

 

A cold front approaching from the northwest will trigger some cells along the front, which may support a weak squall line. The prog tephi profiles along the front suggest gusty winds ,possibly associated with dry microbursts.