Convective Outlook Valid for Today, Tonight and Tomorrow

Regional Impacts

Today: Slight risk of a thundershower over extreme northern New Brunswick and southwestern Labrador this afternoon.

Tonight: No thunderstorms forecast.

Tomorrow: Risk of scattered thunderstorms across New Brunswick and Nova Scotia tomorrow afternoon. Heavy downpours are the main threat.

Convective Discussion…

A slight risk of thundershowers exists today with a slow moving frontal boundary extending from Labrador into southern Quebec. Most of the convection is likely to occur in Quebec today, though a few thundershowers may poke into extreme northern New Brunswick and southwest Labrador as the trough moves east. The 12Z Caribou sounding this morning indicated some modest instability, however a cap was evident around 500 mb. With some smoke aloft over the area of interest, any storms that initiate are likely to remain sub-severe with the main risk being some locally heavy downpours.

A second trough will intensify as it crosses southern Ontario tonight, and draw in some moisture currently over the eastern United States as it approaches New Brunswick tomorrow. Precipitable water from 12Z soundings over the mid-Atlantic region of the US indicate upwards of 50 mm. Though not as high, PWATs across southwestern New Brunswick are expected to rise into the 30 to 40 mm range by tomorrow afternoon as the trough advects some of this moisture north. Weak lapse rates and moist profiles will likely keep any storms from producing strong winds or hail, so the main risk tomorrow is for some heavy downpours, especially in southwestern New Brunswick. There also exists a slight risk for a few pop-up thundershowers over central Newfoundland and southern Labrador tomorrow afternoon.

Thunderstorm Outlook for Today

Thunderstorm Outlook for Tonight

Thunderstorm Outlook for Tomorrow

Forecaster: Copp

Convective Outlook Valid for Today, Tonight and Tomorrow

Regional Impacts

Today: Chance of organized thunderstorms over Cape Breton, Newfoundland and parts of Labrador today. Main hazard is very heavy downpours.

Tonight: Slight risk of an isolated thundershower over eastern Newfoundland.

Tomorrow: Some isolated thunderstorms possible over extreme southwestern Labrador.

Convective Discussion…

A low pressure system with a trailing cold front will be the driver for some organized thunderstorms today across Newfoundland and parts of southeastern Labrador. The cold front prompted severe thunderstorm watches and warnings across eastern Canada and the western Maritimes yesterday, with some organized convection persisting overnight and into this morning. The front will continue to move east today, with a strong stream of moisture being advected in over Newfoundland out ahead of it. The 12Z Stephenville sounding indicates 39 mm of precipitable water and 35 knots of bulk shear, however some warm air evident around 700 mb and weak MUCAPE may inhibit convection from becoming too organized especially given the amount of cloud cover ahead of the cold front. Given adequate clearing though, surface temperatures could rise into the high twenties which could be enough to overcome the warm air aloft and provide just enough energy for some marginally severe storms to develop. Given the high moisture but lack of steep lapse rates, the main threat with any thunderstorms today will be torrential rainfall in the 30 to 50 mm range.

The cold front will quickly move east across Newfoundland this evening, with some isolated thundershowers possible over eastern Newfoundland overnight.

Thunderstorm Outlook for Today

Thunderstorm Outlook for Tonight

Thunderstorm Outlook for Tomorrow

Forecaster: Copp

Convective Outlook Valid for Today, Tonight and Tomorrow

Regional Impacts

Today:

NB: Risk of severe thunderstorms with heavy downpours, strong wind gusts and a non-zero threat of a tornado over Madawaska and western Restigouche county.

NL: Risk of thunderstorms with locally heavy downpours and strong wind gusts.

LAB/PEI/NS: None

Tonight:

Isolated embedded thunderstorms giving locally heavy downpours.

Tomorrow:

NS/NL/LAB: Risk of thunderstorms giving locally heavy downpours.

Convective Discussion

For today, the threat of severe convection increases for northwestern New Brunswick as a low pressure system tracks northeastward over southeastern Quebec and toward Labrador by Friday. Convection has been ongoing this morning along the St. Lawrence towards northern Newfoundland while an MCV materialized ahead of the low centre over the Great Lakes. Looking at the 12Z Caribou sounding and clear skies over much of central and northern Maine and New Brunswick, should convective temperatures be reached (>31C), there is the potential for MLCAPE values of 1000-1500 J/kg, deep 45kt layer shear and further advection of high precipitable water (50 mm) from the Gulf Stream. There may a slight warming in the 500mb temperature leading to a limit in destabilization. However, lift from the approaching cold front as well as the other ingredients will aid in the potential for multicell lines or potential supercells this afternoon and evening across northern Maine and into New Brunswick. Heavy rain and strong wind gusts will be the main threats with convection that develops but there is also a slight threat of a tornado over Madawaska and western Restigouche counties where the SRH values exceed 100.

Troughing over northern Newfoundland continues eastward where some embedded thundershowers may continue into the afternoon where heavy downpours will be the main threat along with brief strong wind gusts.

For tonight into Friday, the cold front associated with the low pressure system will track across the Maritimes tonight and across Newfoundland on Friday giving embedded thunderstorms. As well, moderate to heavy rainfall is likely ahead of the low centre for central and eastern Labrador overnight and throughout Friday.

Thunderstorm Outlook for TODAY

Thunderstorm Outlook for TONIGHT

Thunderstorm Outlook for TOMORROW

 

Roberta McArthur

 

 

Convective Outlook Valid for Today, Tonight and Tomorrow

Regional Impacts

Today:

NB: Risk of thunderstorms giving heavy downpours and gusty winds in the late afternoon.

NS: Slight risk of a thundershower across the spine in the afternoon.

PEI/NL/LAB: None

 

Tonight:

NB: Risk of thunderstorms giving heavy downpours and gusty winds in the evening.

NL: Slight risk of an embedded thunderstorm reaching western region by early morning.

Tomorrow:

NB: Risk of severe thunderstorms with heavy downpours and strong wind gusts.

NL: Risk of thundershowers with locally heavy downpours and strong wind gusts.

LAB/PEI/NS: None

Convective Discussion

The main threat of severe convection today will lie along and ahead of a trough that will moves east to southeastward from north shore Quebec towards the Gaspe Peninsula this afternoon. Organised thunderstorms are not as likely now to reach northern New Brunswick given the timing and position of this trough, but there is still ample deep moisture and daytime heating that anything that does develop will give heavy downpours with water loaded gust potential. Mixed CAPE values are expected to exceed 1000Jkg and with effective shear reaching 35-40kt in northern New Brunswick. This trough will track across the northern Gulf of St. Lawrence and towards Newfoundland by tomorrow morning.

Over Nova Scotia, sea breeze convergence and daytime heating may be enough for a pop-up shower or thundershower across the spine if convective temperatures can be reached. Any cells that do develop will be slow moving and capable of producing localized heavy downpours as cells drift to the southeast.

For tomorrow, the threat of severe convection increases for new Brunswick as a low pressure tracks northeastward over southeastern Quebec and toward Labrador by Friday and a cold front will track into New Brunswick early evening and through the remainder of the Maritimes overnight into Friday.  High MLCAPE, deep 50kt layer shear and high precipitable water (50 mm) will aid in the potential for multicell lines or potential supercells. Meanwhile, the trough from today will impact parts of Newfoundland tomorrow, mostly off the northeast coast where sea breeze and daytime heating will aid in further lift. Heavy downpours are expected to be the main threat but with moderate deep layer shear, some organization into lines is possible.

Thunderstorm Outlook for TODAY

Thunderstorm Outlook for TONIGHT

Thunderstorm Outlook for TOMORROW

 

Roberta McArthur

Convective Outlook Valid for Today , Tonight and Tomorrow

Regional Impacts

Labrador… A few thunderstorms becoming organised over eastern areas. Heavy downpours and strong wind gusts are possible.

Newfoundland… Slight risk of thunderstorms over the northwest this evening and tonight.

New Brunswick…. Slight risk of thunderstorms this afternoon.

PEI… Slight risk of thunderstorms over the west this evening.

NS… little to no impacts today.

 

Convective Discussion

The main area of interest today will be over Labrador, as an unusually high amount of moisture moves into the region, with dew point temperatures approaching 20°C in the east. An approaching surface trough, currently crossing central Labrador, combined with elevated low-level moisture, will increase the potential for thunderstorms. Mixed-layer CAPE values are expected to reach around 1500 J/kg, so rainfall rates exceeding 30 mm per hour are likely.

With the surface trough acting as an organizing feature and low-level shear values in the range of 25–30 knots, there is a chance that storms could organize into a mesoscale convective system (MCS). Overshooting tops and lightning activity should serve as good indicators of which storms are severe. Equilibrium levels for the more intense storms are expected to be around -50°C, which should help distinguish the severe cells.

This situation is expected to evolve rapidly this afternoon as solar insolation and the approaching trough initiate thunderstorm development. Alerts may be required. Strong wind gusts and small to moderate hail are also possible with the storms.

Over New Brunswick, conditions are expected to be somewhat less dramatic. While wind shear values are favorable — with over 40 knots of deep-layer shear — thunderstorms may struggle to develop due to relatively thin CAPE. The strong shear may, in fact, inhibit deep convective growth. Although a few cells capable of producing lightning may form over northern New Brunswick, it is unlikely they will evolve into long-lived, organized thunderstorms.

The situation is likely to be conducive for organised thunderstorms over New Brunswick and Nova Scotia to a lesser extent tomorrow. Over NB deep shear values should still be quite high but the potential from higher CAPE values and updraft potential will be more likely to produce severe storms.

 

Thunderstorm Outlook for Today

Thunderstorm Outlook for Tonight

Thunderstorm Outlook for Tomorrow

 

 

Mel Lemmon