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

Convective Outlook Valid for Today, Tonight and Tomorrow

Regional Impacts

Isolated non-severe thunderstorms are possible this morning along portions of South Shore NS and offshore across marine areas – slope waters, and Sable Island. Elsewhere across Maritimes the atmosphere is stabilizing.

 

Convective Discussion

Soundings behind the frontal feature are drying out nicely at 700mb as forecast. This is stabilizing the mid levels of the atmosphere with the noticeable change in air mass. No thunderstorms are forecast overnight tonight across the AOR. Pockets of instability are possible in parts of central Newfoundland tomorrow, along parts of the Lab coast, and across extreme northern NB. No dynamics suggest anything near severe limits. Cells will be embedded in shower activity. Sunday late in the day has the potential to be more organized in NB and NS as a frontal feature amps up dew points and lift indices again. This risk will be honed in on in coming shifts, with a particularly watchful eye on shear.

 

Thunderstorm Outlook for TODAY

 

Thunderstorm Outlook for TONIGHT

 

Thunderstorm Outlook for SATURDAY

 

Thunderstorm Outlook for SUNDAY

 

Forecaster: Tirone

Convective Outlook Valid for Today, Tonight and Tomorrow

Regional Impacts

NS/NB/PEI… Scattered thunderstorms possible across the central Maritimes this afternoon, main risks are heavy downpours, strong wind gusts, and small hail.

NLFD… Isolated thunderstorms possible in central Newfoundland this afternoon, main risks are strong wind gusts and heavy downpours.

 

Convective Discussion…

As very warm temperatures continue across the Maritimes today, a cold front will begin to move south across the region. Surface based CAPE values are forecast to soar upwards of 2000 J/kg in southern New Brunswick and mainland Nova Scotia ahead of the front in addition to decent bulk shear values of 30 to 35 kts. Due to the strength of the ridge south of Nova Scotia, the front is expected to slow down and weaken as it moves across New Brunswick, and stall over southern Nova Scotia tonight. This will cause some issues in the erosion of the thermal ridge, especially over southern Nova Scotia. In addition, the location of the 500 mb jet over central Quebec is not ideal. As such, the main focus for severe thunderstorms will be in southeastern New Brunswick and central Nova Scotia today. PWAT values on the Yarmouth tephigram this morning indicate 45 to 50 mm, which is consistent with what models have been forecasting ahead of the front. With these high PWAT values, heavy downpours of 25 to 50 mm/h are expected to be the main hazard with any thunderstorms that develop, in addition to strong wind gusts of 70 to 90 km/h and small hail up to dime size.

A second round of convection may move through southern Nova Scotia from the west overnight tonight, as a weak shortwave rides the thermal ridge across the region. Heavy downpours may company these storms if they persist over the Gulf of Maine.

In central Newfoundland, similar conditions to central Nova Scotia are expected, however bulk shear values are likely to be slightly lower here (20 to 25 kts), which may prevent more organized thunderstorm activity. Another limiting factor is a layer of warmer air evident in the mid levels persisting over central Newfoundland today. Any thunderstorms that do develop may struggle to get organized, but may produce strong wind gusts of 70 to 90 km/h and heavy downpours up to 25 mm/h, in addition to the small chance of some pea sized hail.

 

Thunderstorm Outlook for Today

Thunderstorm Outlook for Tonight

Thunderstorm Outlook for Tomorrow

Copp