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

Convective Outlook Valid for Today , Tonight and Tomorrow

Regional Impacts

Today

NB: Isolated to scattered thundershowers giving brief strong wind gusts and small hail.

Lab: Isolated thundershowers over the extreme western sections.

NS/PEI/NL : Nil

Tonight

NB/NS/PEI/NL/LAB: Nil

Tomorrow

NB : Isolated thundershowers over northern and southern sections of the province.

NS: Isolated thundershowers along the western coast of the province.

Lab: Isolated thundershowers over the western sections.

Convective Discussion

Today, a weak riding over the Maritimes is expected to erode throughout the day. As this ridging erodes there is expected to be a sea-breeze form in the late afternoon which, along with day-time heating, will act as a trigger for convection in New Brunswick. The areas that have the formation of sea-breezes, and topographic enhancement will have the greatest chance to form storms that are able to produce longer lasting storms able to produce these winds near 70 km/h and hail over 1cm. With moderate dew points, and more than sufficient MUCAPE and MLCAPE, the main limiting factors for today is going to come down to windshear. There is troughing at the 850mb and 700mb levels which is allowing for convection to become more organized; however, without strong enough jet support todays storms are primed to be single cell and isolated in nature. Likewise for Western Labrador, the thunderstorms for today do not appear to have sufficient jet support to give rise to significant storms and are expected to be isolated in nature.

Tonight, with temperatures and sea-breezes being the most significant trigger for today, once temperatures begin to cool and the sea-breeze ceases the mechanisms for today’s storms will begin to shutdown. There is a risk in the early evening that any existing storms could become more elevated and persist slightly into the later evening hours. However, any storms that become elevated are expected run out of support quickly into the evening hours.

Tomorrow, there is an approaching frontal system coming from Ontario. With this system moving in there is a risk for isolated embedded thunderstorms as the warm sector approaches the Maritimes.  Additionally, as this system is approaching there is expected to be a Northwest flow that forms over the Eastern Maritimes and Southwestern Newfoundland regions. This flow could give rise to isolated thundershowers in upslope flow, however predictability on this setup producing thunderstorms is low and as such was not put into the outlook.

Thunderstorm Outlook for Today

Thunderstorm Outlook for Tonight

Thunderstorm Outlook for Tomorrow

Forecaster: Lambert/McArthur

Convective Outlook Valid for Today, Tonight and Tomorrow

Regional Impacts

Today

NS: Chance for embedded thundershowers across Cape Breton early this afternoon and isolated thundershowers in northern Nova Scotia this afternoon with brief wind gusts and a risk of small hail.

NB: Chance of isolated thundershowers in the southeast in the afternoon with a risk of brief wind gusts and small hail.

NFLD: Chance for elevated thundershowers.

PEI/Lab: None.

Tonight

Isolated embedded thundershowers over the Grand Banks and southern NL

NS/NB/PEI/LAB : None

Tomorrow

NB/NS: Isolated to scattered thundershowers giving brief strong wind gusts and small hail.

NL: Isolated embedded thundershowers over the Avalon Peninsula.

LAB/PEI: None

Convective Discussion

Today, a frontal system currently across the Gulf of St. Lawrence will slowly progress eastward and begin to slow down over Cape Breton and Southern Newfoundland tonight. The risk of embedded convection continues along the trough today and tonight. In behind the frontal system, clearing of the cloud with still moderate dew points will aid in increasing instability in the afternoon. There is a narrow corridor of Mixed CAPE nearing 500 J/Kg with effective shear of 20 to 30Kt due to an 850 mb LLJ giving rise to the possibility of some organized thundershowers from Southeast New Brunswick into central Nova Scotia late afternoon and early evening. Brief strong wind gusts and small hail less than 1 cm are expected. 

Tomorrow, a weak ridge over the Maritimes will erode, and with the aid of increasing moisture and convective temperatures along with an approaching jet streak from the west and sea breeze convergence, isolated to scattered showers with a risk of thundershowers will develop in the afternoon. The highest risk of storms is over central and northern New Brunswick, where freezing levels are fairly low and MUCAPE values are expected to reach 1500 J/kg. Shear is only light to moderate at or below 20kt, so expecting more pulse like storms with brief wind gusts, heavy rain and small hail of 1-2cm. Seabreeze convergence may also aid in a brief showers in the spine of NS, PEI and southern NB.

The risk of embedded thundershowers continues along the trough across the Avalon southeastward towards the Grand Banks as well tomorrow as the trough slowly pulls away to the southeast.

Thunderstorm Outlook for Today

 

Thunderstorm Outlook for Tonight

Thunderstorm Outlook for Tomorrow

Forecaster: McArthur