Convective Outlook Valid for Today and Tomorrow

Thunderstorm Outlook for Day 1

Slight chance of thunderstorms, except some local downpours for southwest Labradors, and some possibly significant rainfall and gusty winds for western New Brunswick.

 

Convective Discussion

N-S ridge over eastern Newfoundland with a nearly vertically stacked deep trough from western Labrador to New Brunswick then extending towards Cheasapeake Bay. There are embedded lows for Labrador, New Brunswick, and near Cape Cod. As with yesterday, many of the profiles are moist adiabatic and tropical, with 40-50 mm PWATs and ample surface moisture, with surface dew points near 21 C. Shears are about 25 kts near the trough increasing to 40 for central Nova Scotia then dropping back to 24 for eastern regions.

 

For Labrador the low has a frontal trough extending east towards Mary’s Harbour, and the low will move steadily east.  There is some Cuing up near and west of the low, and some isolated thundershowers are possible. Ahead of the front there should be TCu’s possibly with a strike or two, but with some heavy downpours being the main factor.  PWATs are about 40 mm and Capes may approach 500 J/kg, but the capping inversion may have some trouble breaking.

 

For New Brunswick, especially in the west the story is similar, but with more energy and surface moisture, with energy peaking late in the afternoon  near 500-1000 J/kg, with surface dewpoints near 20 C and the main moisture axis through the center of the province. The shear is low at about 25 kts, so supercells probably won’t be an issue. The impacts will be airmass cells with heavy downpours and some gusty winds.

 

 

 

Thunderstorm Outlook for Day 2

 

Convective Outlook Valid for Today and Tomorrow

Thunderstorm Outlook for Day 1

Rain with heavier convective downpours for the Atlantic Coast of Nova Scotia, with isolated lightning and some gusty winds. A weak area of convergence may spark up some cells for southwestern Labrador.

 

 

Convective Discussion

The main threat for today, and especially for tomorrow, is due to the influence of the remnants of Henri as it approaches and then moves through the Maritimes. Henri is a vertically stacked system up to 250 mb, within a vertically stacked trough, again up to 250 mb. There’s a frontal trough extending south then southwest of the low, and it is approaching the western Maritimes today. Moisture is good with near 22 mm dewpoints at the surface extending above 850 mb. PWATs are up to 50 mm. Also, east of the system there is a fre-frontal band  with a  low level jet extending up to 500 mb. The tephis show a roughly moist adiabatic profile ahead of the system, so not a lot of CAPE (~ 300-600 j/kg), with deep layer shear less than 25 kts. So basically local heavy downpours, some gusty winds, and maybe some lightning.

 

Highest rainfall amounts are likely for tonight into tomorrow. Late today into this evening it will start over the Atlantic Coast of Nova Scotia,  then spread north.

 

Thunderstorm Outlook for Day 2

 

Basically the same story with the rainfall propagation east. The main system will be moving into New Brunswick, with some likelihood for isolated  cells for the Long Range Mountains of Newfoundland.

Convective Outlook Valid for Today and Tomorrow

Regional Impacts

 

Labrador…Risk of thundershowers this evening over western sections.

 

Convective Discussion

 

A trough moves in from central Quebec tonight into western Labrador, extending from a low pressure system over Hudson Bay. This trough is expected to bring in showers and a risk of thundershowers over central Quebec which may continue into this evening into western Labrador as the area is under the influence of moderate 0-6km shear and PWATs near 30 mm.

 

Tropical Storm Henri will soon be making landfall in New England or eastern Long Island, and weaken into a depression then a post-tropical storm on Monday. Outer rain bands well north and east of the centre with heavy rainfall possible will move over the Maritime southwestern marine district today and tomorrow.

 

 

Thunderstorm Outlook for Day 1 – August 22, 2021

 

 

Thunderstorm Outlook for Day 2 – August 23, 2021

 

Convective Outlook Valid for August 21st and 22nd

Thunderstorm Outlook for Day 1

 

Regional Impacts

None

 

Convective Discussion

With a ridge of high pressure dominating the area, there is no risk of severe thunderstorms today.  A trough moves in from the west Sunday night over western Labrador bringing a risk of thundershowers.

 

 

Thunderstorm Outlook for Day 2

Convective Outlook Valid for Today and Tomorrow

Thunderstorm Outlook for Day 1

 

Some heavy downpours and local gusty winds with isolated thunderstorms, mainly  for New Brunswick  and southern Newfoundland. Otherwise noting significant expected for today and tomorrow.

 

Convective Discussion

 

The main area of interest is southern Newfoundland and New Brunswick. To the north there is too much shear (~40-60 kts)  and not enough moisture (PWATs 20 mm or less), combined with  a ridge building in from the west.

 

Currently there is a trough extending east over Newfoundland and southwest over the Maritimes from a developing weak low over the Gulf. The low will track over southern Newfoundland today and tonight. For New Brunswick there are currently some stable layers that will destabilise somewhat with the trough and daytime heating, combined with surface dewpoints between 18-22 and PWATs fairly healthy in the 35-55 mm range. There is little shear (~12-22 kts) arguing for airmass pop-ups. Farther north there is less upper support but more daytime heating. For both cases CAPEs on the order of 500 J/kg are possibly. The low shear and good moisture argue for airmass pop-ups with local heavy downpours and brief gusty winds.

 

For Newfoundland the stability this morning was higher, with the developing low hopefully destabilising aloft and giving some lift from convergence below. The moisture is a bit less with PWATS near 35 mm, but the dewpoints are only a couple of degrees cooler than the Maritimes. So the impacts should be similar, but possibly with the training along the trough-low-topography combination.

 

 

 

 

 

 

Thunderstorm Outlook for Day 2

 

Good news.