Convective Outlook Valid for Today, Tonight and Tomorrow

Regional Impacts

Today

NB: Chance of some scattered thundershowers over western New Brunswick this afternoon with some locally heavy downpours.

Lab: Chance of some isolated thundershowers through central Labrador this afternoon.

NS/PEI/NFLD: None.

Tonight

NS/NB/PEI/NFLD/LAB : None.

Tomorrow

LAB: Risk of some marginally severe thunderstorms over southern Labrador in the afternoon with small hail, strong wind gusts, and locally heavy downpours.

NS: Risk of an elevated thundershower over southern mainland Nova Scotia through the day.

NB/PEI/NFLD: None.

 

Convective Discussion…

A ridge of high pressure sits over central Atlantic Canda this morning with a weak surface trough extending from central Maine up into central Quebec, just west of Labrador. This trough will be the main focus for any convection today, as it slowly begins to move east. A small but strong upper low over central Ontario will combine with a shortwave near New England and approach the trough this afternoon, which will act as the main trigger for convection. MLCAPE values over western New Brunswick are forecast to be around 500 to 750 J/kg today, with effective shear around 15 to 25 knots. One of the limiting factors however is how quickly the shortwave is advected East into New Brunswick, as well as some warm air aloft between 500 and 700 mb. This could limit the higher shear and some better thermodynamics from reaching the risk area until later this evening, which would lead to more isolated and short-lived thundershowers this afternoon. The risk for more organized storms could still increase into this evening however as the shortwave approaches, which could be capable of producing some locally heavy downpours of 10 to 20 mm per hour.

There is also a slight risk of some isolated thundershowers with a weak trough over central Labrador today which is in a similar environment to western New Brunswick, however there is a lack of moisture evident over this area which will reduce the risk of storms here today. Current surface observations show dewpoints only in the 5 to 7 degree range, with temperatures already above 20. Nonetheless, the potential for some isolated thundershowers exists which could produce some gusty winds.

Tonight, the shortwave will reach the Gulf of Maine, bringing with it the risk of an elevated thundershower over the marine areas west of Nova Scotia in the early morning hours. Into tomorrow, the shortwave will track across Nova Scotia, continuing to bring the chance for an elevated thundershower across the southern half of the mainland during the day and into the evening. Elsewhere, the upper low currently over central Ontario will sit over central Quebec by tomorrow morning with today’s surface trough now extending east from the upper low into southern Labrador. This will be the main focus for convection tomorrow, as MLCAPE values in the warm sector just south of the trough could reach 750 to 1000 J/kg by the afternoon. Slightly better moisture being advected in from the south and effective shear in the range of 20 to 30 knots should be sufficient to get some organized, marginally severe thunderstorms tomorrow afternoon. The surface trough is initially forecast to remain fairly stationary before eventually shifting south in the late afternoon/early evening. This in combination with an expected easterly storm motion could lead to some multi-cell training storms early in the day which would increase the risk of heavy rainfall for some areas. Some small hail and strong wind gusts are also possible with these storms. Luckily, the main risk area is expected to remain over unpopulated areas but could impact a few communities early in the 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

NS… Chance of thunderstorms today, some heavy downpours possible.

NB.. Chance of thunderstorms today and tomorrow. Heavy downpours possible with small hail.

PEI.. No thunderstorms expected.

Newfoundland.. No thunderstorms expected.

Labrador.. Low chance of thunderstorms expected tomorrow.

Convective Discussion

Instability will persist over western areas today as an upper trough slowly exits the region. CAPE values are expected to remain modest, reaching around 1000 J/kg, with generally weak low-level shear and deep-layer shear staying below 25 knots across most of New Brunswick.

As a result, severe thunderstorms are unlikely. However, isolated cells may still produce small hail and locally heavy downpours.

Looking ahead to tomorrow, shear will increase somewhat, but the relatively cool airmass will limit the available energy for convection. Non-severe showers or thunderstorms may once again develop over western areas. With limited heating and only modest increases in dew points expected in the coming days, overall conditions are not anticipated to change significantly.

Thunderstorm Outlook for Today

Thunderstorm Outlook for Tonight

Thunderstorm Outlook for Tomorrow

Convective Outlook Valid for Today , Tonight and Tomorrow

Regional Impacts

NB: Low chance of thunderstorms this evening, with little to no impacts expected.
NS: Some thunderstorms possible today, mainly over eastern areas. Locally heavy downpours and gusty winds possible.
Labrador: Low chance of thunderstorms today, no significant impacts expected.
Newfoundland: Low chance of thunderstorms today. Western/interior areas may see locally heavier rain.
PEI: Slight risk of thunderstorms today, with brief heavier showers possible.

Convective Discussion

A weak low pressure system over the region will continue to track northeastward today, with an associated surface trough moving across Nova Scotia through the day. Low-level convergence along this trough, as well as over parts of Newfoundland, will support isolated thunderstorm development.

Across Nova Scotia, the convective window will be relatively short-lived, ending by late afternoon as the trough exits. Slightly higher CAPE and shear in this region may support locally heavier rainfall rates and a risk of gusty winds in any storms that develop.

Over Newfoundland, thunderstorm activity may persist into the evening hours, with locally heavier downpours embedded within broader area of shower activity.

Over western Labrador, a weak thunderstorm cannot be ruled out, though no impacts are expected.

Looking ahead to Sunday into Monday, generally unsettled conditions will continue over New Brunswick and parts of Nova Scotia, with occasional weak thunderstorms possible.

Thunderstorm Outlook for Today

Thunderstorm Outlook for Tonight

Thunderstorm Outlook for Tomorrow

 

Mel Lemmon

Convective Outlook Valid for Today , Tonight and Tomorrow

Regional Impacts

NB.. Low chance of thunderstorms today, strong gusts possible if thunderstorms form.

NS.. Some thunderstorms possible tomorrow with heavier downpours.

Labrador.. low chance of thunderstorms today.

Newfoundland.. Low chance of embedded thunderstorms today over the east. Low chance of weak thunderstorms tomorrow interior.

PEI.. Slight risk of thunderstorms this evening.

 

Convective Discussion

Some dynamic support exists for convection today, though cooler temperatures and low dew points will limit updraft potential. Any storms that develop may produce locally strong wind gusts due to enhanced downdraft potential.

A low chance of embedded thunderstorms exists over eastern Newfoundland, with no expected impacts.

For tomorrow, a low-probability but higher-impact scenario exists over eastern Nova Scotia if training develops; localized rainfall rates near 25 mm/h are possible.

Sunday may be more active as another upper trough crosses the region. Modest instability and shear could support heavier downpours and small hail.

 

Thunderstorm Outlook for Today

Thunderstorm Outlook for Tonight

Thunderstorm Outlook for Tomorrow

Convective Outlook Valid for Today, Tonight and Tomorrow

Regional Impacts

Today

NB: Chance of an isolated thunderstorm over northern NB early this afternoon with small hail and strong wind gusts. Slight risk of an elevated thundershower with heavy downpours this evening over southwest NB.

NS: Slight risk of an elevated thundershower with heavy downpours this evening over extreme southwestern Nova Scotia.

LAB: Chance of an isolated thunderstorm over western Labrador this afternoon and early this evening with small hail and strong wind gusts.

PEI/NFLD: None.

Tonight

NB/NS/PEI: Chance of some elevated thundershowers overnight.

NFLD/LAB: None.

Tomorrow

NB/NS: Slight chance of some isolated thundershowers in the afternoon.

NFLD: Chance of some elevated thundershowers over southern Newfoundland through the day.

PEI/LAB: None.

 

Convective Discussion…

After a fairly active day across New Brunswick yesterday, a trough of low pressure will approach from New England this afternoon, reaching the western Maritimes by early this evening. There exists a few threat areas today, the first of which being associated with the aforementioned trough. Some lightning activity is already being observed across the eastern United States with this feature, and is expected to continue as it moves east through the day. The risk for thundershowers is expected to diminish in this trough as it approaches the Maritimes, however MUCAPE values may still rise to 250 to 400 J/kg over southwestern New Brunswick and Nova Scotia this evening. With near 40 knots of effective shear, there should be enough instability to allow for an elevated thundershower or two late this evening. The 12Z Upton, New York sounding indicated 43 mm of precipitable water, leading to the potential for some heavy downpours of 10 to 20 mm per hour over the risk area. Overnight, as the trough moves east across the Maritimes, there exists the potential for an elevated thundershower or two over PEI and Nova Scotia as well as southeast New Brunswick, but these are not expected to produce any significant hazards. This threat area will continue into southern Newfoundland through the day tomorrow.

Another area of interest exists over northern New Brunswick and western Labrador this afternoon, which is in a similar environment that produced some small hail and marginally severe storms over New Brunswick yesterday. SBCAPE values over this area could reach over 1000 J/kg, however a lack of effective shear (10 to 15 knots) will likely lead to a very short life span of any storms that develop this afternoon. Nonetheless, low freezing levels give the potential for some brief pea sized hail as the storms peak in intensity. The threat over New Brunswick will diminish into the late afternoon, as cloud cover from the approaching trough will cut off the energy needed to trigger these storms.

Tomorrow, the low pressure centre associated with the trough will cross northern New Brunswick. Given enough clearing over southern portions of the province, SBCAPE values could build up to 750 J/kg, giving enough energy to produce some isolated thundershowers in the afternoon. Even though effective shear is expected to be a bit higher than today (20 to 30 knots), fairly weak lapse rates should keep any storms from becoming severe.

Thunderstorm Outlook for Today

Thunderstorm Outlook for Tonight

Thunderstorm Outlook for Tomorrow

Forecaster: Copp