Regional Impacts
Maritimes: None today and Saturday.
NFLD/Labrador: A risk of thundershowers this afternoon and evening over central/eastern Newfoundland and southern Labrador. None on Saturday.
Convective Discussion
Just a chance of embedded thundershowers in Newfoundland today. Over southern Labrador, a few surface based thundershowers are possible this afternoon but the shear is very low so they will be short lived.
Thunderstorm Outlook for Day 1
Regional Impacts
New Brunswick: Isolated to scattered thundershowers this afternoon and evening. Potential severe thundershowers giving downpours, gusty winds and hail.
NS/PEI/ NFLD/Labrador: A risk of thundershowers this afternoon and evening.
Convective Discussion
A cold front will approach northern New Brunswick this afternoon. ML cape values near 1000 J/kg are expected and wind shear near 30 kts. Freezing levels are high but decent cape exists in the hail growth zone. Dry mid layers will allow for gusty conditions. PWAT values will be near 40 mm so rainfall is a concern. The upper dynamics are supportive as well this afternoon as a strengthening diffluent trough approaches ahead of the main 250 mb jet. There is also possible rotation as the helicity values will be over 100.
Thunderstorm Outlook for Day 1
Thunderstorm Outlook for Day 2
Regional Impacts (Day 1)
None
Convective Discussion (Day 1)
None
Thunderstorm Outlook for Day 1
Regional Impacts (Day 2)
New Brunswick: Isolated to scattered thundershowers tomorrow afternoon and evening. Potential severe thundershowers giving downpours, gusty winds and hail.
NS/PEI/Labrador: A risk of thundershowers tomorrow afternoon and evening.
NFLD: Nil.
Convective Discussion (Day 2)
A cold front will cross northern New Brunswick tomorrow afternoon and evening. ML cape values near 1000 J/kg are expected and wind shear near 30 kts. Freezing levels are high but decent cape exists in the hail growth zone. Dry mid layers will allow for gusty conditions. PWAT values will be near 40 mm so rainfall is a concern. The upper dynamics are supportive as well.
Thunderstorm Outlook for Day 2
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
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.
