Convective Outlook for Weekend of Aug 28-29th

Thunderstorm Outlook for TODAY – Saturday, August 28, 2021

 

Regional Impacts

None expected at this time.

 

Convective Discussion

A strong ridge is building in from the west today, and with it is increasing atmospheric stability. Additionally, a northerly flow last night over much of the region dried out the muggy airmass. The cold front is exiting Newfoundland’s marine waters this afternoon, and there are no other forcings at play today.

 

 

 

Thunderstorm Outlook for TOMORROW – Sunday, August 29, 2021

 

Regional Impacts

None forecast.

 

Convective Discussion

Ridge still keeping atmosphere stable and dry in lower and mid levels. Invading high cloud also a deterrent.

 

 

*Forecaster: TIRONE

 

end/ASPC

Convective Outlook Valid for Today and Tomorrow

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

 

Convective Outlook Valid for Today and Tomorrow

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

 

 

 

Convective Outlook Valid for Today and Tomorrow

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

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