Convective Outlook Valid for Today, Tonight and Tomorrow

Regional Impacts…

NB… Scattered thunderstorms possible over northwestern New Brunswick early this afternoon. Rainfall rates of 10 to 20 mm/h and wind gusts up to 70 km/h.

NL… Isolated thunderstorms possible over southwest Labrador this afternoon. Rainfall rates of 10 to 20 mm/h and wind gusts up to 70 km/h.

NS/PEI… Embedded thundershowers possible tomorrow morning and afternoon. Rainfall rates of 10 to 20 mm/h.

 

Convective Discussion…

A trough entering New Brunswick today brings the risk for some scattered thunderstorms early this afternoon. The biggest threat for severe weather exists in northern New Brunswick, where better thermodynamics and forcing are present. However, dense cloud cover northern New Brunswick is preventing CAPE values from rising too much, though some brief clearing behind this is expected. The risk remains low due to this, in addition to a stalling thermal trough this afternoon. The thermal ridge sitting over southern New Brunswick should remain intact and inhibit much thunderstorm activity here today, as the frontal boundary slows down and stalls over northern New Brunswick later this afternoon. Bulk shear values of 40 to 50 kts are present (though quite linear), as well as PWAT values in the range of 30 to 35 mm. As such, the main threats with any storms today will be strong wind gusts up to 70 km/h and heavy downpours of 10 to 20 mm/h.

A second system, that is expected to bring severe weather to parts of the northeast US today, will approach the Maritimes over the Gulf of Maine tonight, reaching southwest Nova Scotia early tomorrow morning. Strong dynamics and adequate instability in the mid-levels will aid in sustaining convection overnight and into tomorrow morning as the trough passes over the Gulf of Maine. With PWAT values expected around 40 to 50 mm, heavy downpours up to 20 mm/h are possible tomorrow morning across southern Nova Scotia and potentially into the Bay of Fundy.

 

Thunderstorm Outlook for Today

Thunderstorm Outlook for Tonight

Thunderstorm Outlook for Tomorrow

Copp

Convective Outlook Valid for Today, Tonight and Tomorrow

Regional Impacts

NS/NB/PEI… Isolated thundershowers today producing locally heavy downpours of 10 to 20 mm/h.

NL… None.

 

Convective Discussion…

A low passing south of Nova Scotia today brings a slight chance for some isolated thundershowers over portions of the central and eastern Maritimes. Meager MLCAPE values of less than 500 J/kg, and weak bulk shear might be enough to squeeze out a few lightning strikes, but no organized convection is expected. Nonetheless, a steady stream of moisture around the northern side of the low will provide PWAT values in the range of 25 to 30 mm, so locally heavy downpours of 10 to 20 mm/h will be possible this afternoon. The risk will quickly diminish this evening as the low approaches Newfoundland.

Tomorrow, a trough will approach western Newfoundland and northern New Brunswick, bringing the risk for some isolated thunderstorms in the afternoon. A slightly better environment for severe weather is in place in northern New Brunswick, with higher CAPE and bulk shear values present tomorrow. The limiting factor is the timing of the thermal trough, as current guidance doesn’t have it moving through until 21Z, thus the risk currently remains low for organized thudnerstorms.

 

Thunderstorm Outlook for Today

Thunderstorm Outlook for Tonight

Thunderstorm Outlook for Tomorrow

Copp

Convective Outlook Valid for Today, Tonight and Tomorrow

Regional Impacts

 

NS and PEI

Today… Isolated thunderstorms giving amounts of 15 to 25 mm.

Tuesday… Isolated thunderstorms.

 

NB

Today… Isolated thunderstorms likely, especially over southern sections giving amounts of 15 to 25 mm.

Tuesday… Isolated thunderstorms likely, especially over southeastern sections.

 

NF

Today… Isolated thunderstorms likely, especially over southern sections giving amounts of 15 to 25 mm.

Tuesday… None.

 

Labrador

Today… Risk of thunderstorms south of the Churchill river – East to Eagle river – and then Cartwright area with a risk of small hail and brief wind gusts.

Tuesday… None

 

 

Convective Discussion

 

An area of low pressure currently centred over Maine will slowly track eastward today to lie over Nova Scotia by Tuesday morning then should track towards the northeast over Newfoundland by Wednesday morning. There has been ongoing elevated embedded convection ahead of this low, from off Cape Hatteras stretching northeast towards southern Newfoundland, aided by a strong upper jet and very warm air near 850mb. Some rainfall amounts of upwards of 50 mm have already fallen since yesterday over parts of the Maritimes and southern Newfoundland. Embedded convection is expected to continue today and into Tuesday and the low moves eastward. 12Z soundings from YQI and YAW indicate precipitable water near 45 mm, but with a strong mean flow ahead of the low centre from the southwest (50KT at 700mb), convection is moving through quickly. However, closer to the centre of the low in southern Maine and southwestern New Brunswick, convection is also expected this afternoon but will be slower to move so there is the risk of locally heavy downpours.

 

Meanwhile, a trough over southern central Labrador along with some clear skies this morning will aid in increased instability and surface convection for this afternoon for areas of southern and southeastern Labrador. MUCAPE may reach 500 J/kg but 0-6km shear above 50kt may prohibit much convection from maintaining for long but there is the risk of small hail and brief strong wind gusts.

 

 

Thunderstorm Outlook for Today

 

Thunderstorm Outlook for Tonight

 

Thunderstorm Outlook for Tomorrow

Convective Outlook Valid for Today , Tonight and Tomorrow

Regional Impacts

Labrador

Today…Isolated non-severe thunderstorms over southern sections

Monday…Risk of non-severe thunderstorms south of the Churchill river – East to Eagle river – and then Cartwright area

 

NF

Today…Slight Risk of a non-severe thunderstorm over northeastern sections

Monday…Rain and Isolated embedded thunderstorms over southern sections giving some heavier rain (15-30 mm)

 

NB

Today…Rain spreading throughout the province with embedded thunderstorms giving higher amounts (30-60 mm through tonight)

Monday…Isolated thunderstorms likely, especially over southern sections

 

NS and PEI

Today…Rain spreading from west to east and with a few embedded thunderstorms likely giving amounts of 20-40 mm

Monday…Rain with Isolated embedded thunderstorms giving amounts of 10 to 15mm

 

 

Convective Discussion

Some weak surface-based instability is expected over southern Labrador today the main forcing is a convergence line between the mid-coast and the southwest corner. The main limiting factor is the lack of moisture near the surface, however Td of 9 or 10 deg and temperatures of 20 to 25 were sufficient to trigger isolated CB’s. Using this combination on the 12z Goose sounding yielded MLCAPE values in excess of 500 J/kg, LI of 0 or -1, and equilibrium levels to almost 20,000 ft

The main threat of severe weather lies west of the region today, between southern QC and NE where a number of upper air soundings revealed curved hodographs this morning. Atlantic provinces will be under the influence of a low pressure system which will travel from the Ottawa valley through the Gulf of St. Lawrence then NF tonight and Monday. Some of the forecast guidance is suggesting rainfall amounts enhanced significantly by embedded convection, generally along the track of the low, amounts of 50 to 75 mm can be expected with hints of 100+ west of the region.

 

Thunderstorm Outlook for Today

 

 

Thunderstorm Outlook for Tonight

 

 

Thunderstorm Outlook for Tomorrow

Convective Outlook Valid for Today , Tonight and Tomorrow

Regional Impacts

 

Labrador

Today…Risk of a non-severe thunderstorm over southeastern sections during the afternoon, and late in the day in the west

Sunday…Risk of a non-severe thunderstorm over southernmost sections

 

NF

Today…Isolated non-severe thunderstorms over central and northeast sections

Sunday…Risk of a non-severe thunderstorm especially over northeast sections

 

NB

Today…Risk of a non-severe thunderstorm over northern regions, especially the Chaleur region

Sunday…Heavy rain likely from embedded thunderstorms

 

NS and PEI

Today…none

Sunday…Rain with Isolated embedded thunderstorms

 

 

Convective Discussion

The main area of focus this afternoon is over central NF. The convective temperature should be reached fairly early in the period but low level moisture is low and the deep layer shears are too high to produce more widespread / deeper convection. Regardless, conditions will likely produce moderate TCU’s (and even one or two CB’s) with local 5-10 mm and gusts around 50 km/h. For Lab west, there is an approaching surface trough with a large area of cloud is associated with it. Satellite imagery is indicating the presence of embedded convections west of Schefferville (however there is no lightning activity detected). The moisture in the low levels is clearly lacking over YKL-ZUM-YWK but Td’s should increase during the afternoon.. this combined with the long period of early summer surface heating, and the emergence of a low and upper level jet – should provide some support for the development of deeper (moderate) convection ahead of this feature. Having formed in a low moisture environment, rainfall rate potential is 5 mm/h at the most.  

A frontal band over New England will shift north on Sunday and spread rain across the Maritimes. Rainfall rates will be enhanced by embedded thunderstorms, especially over NB

 

 

Thunderstorm Outlook for Today

 

 

Thunderstorm Outlook for Tonight

 

 

Thunderstorm Outlook for Tomorrow