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

Convective Outlook Valid for Today , Tonight, Tomorrow, and Wednesday

Regional Impacts

Today

NS: Chance for elevated thunderstorms spanning Southwestern Nova Scotia through Central Nova Scotia. Risk for gusts of 60 to 70 km/h and rainfall of 20mm.

PEI: Chance for elevated thunderstorms spanning the province. Risk for gusts of 60 to 70 km/h and rainfall of 20mm.

NB: Chance for elevated thunderstorms in the Southeast sections of the province. Risk for gusts of 60 to 70 km/h and rainfall of 20mm. Slight chance of an Isolated thundershower over extreme Northwestern New Brunswick.

NFLD/LAB: Nil.

Tonight

NS: Chance for elevated thundershowers spanning Southwestern Nova Scotia through Central Nova Scotia. Risk for gusts of 60 to 70 km/h and rainfall of 20mm.

PEI: Chance for elevated thundershowers spanning the province. Risk for gusts of 60 to 70 km/h and rainfall of 20mm.

NB: Chance for elevated thundershowers in the Southeast sections of the province. Risk for gusts of 60 to 70 km/h and rainfall of 20mm. Slight chance of an isolated thundershower over extreme Northwestern New Brunswick.

NFLD/LAB: Nil.

Tomorrow

NS: Chance for elevated thundershowers spanning Central Nova Scotia through Cape Breton.

PEI: Chance for elevated thundershowers spanning the province in the morning.

NB: Chance for elevated thundershowers over the majority of the province.

NFLD: Chance for elevated thundershowers over the extreme Southwest and South-central regions of the province.

Lab: Nil

Wednesday

NS: Chance for isolated thunderstorms predominantly over the Central regions of the province.

PEI: Chance for isolated thunderstorms over the province.

NB: Chance for isolated thunderstorms over the interior of the province. Risks include gusts of 70-80km/h and hail near 2cm.

NFLD: Chance for elevated thundershowers over the Southern and Central regions of the province.

LAB: Nil.

 

Convective Discussion…

An approaching frontal system is progressing through the Atlantic Canada today is eroding the previously placed high pressure system throughout today and tomorrow.

Today, the main threat area will be in the Southeastern sections of New Brunswick and over most of mainland Nova Scotia where elevated thunderstorms could produce heavy downpours with rainfall possibly exceeding 20mm of rain and wind gusts of 60 to 70km/h. From ship observations there was reports of winds in excess of 60km/h. Current satellite imagery shows the approaching frontal system with embedded thunderstorms over the marine regions from overnight approaching the Nova Scotia coast. This should allow the continuation of MUCAPE to near 600 J/Kg, along with PWAT’s to remain near 30-40mm by this afternoon and progress eastward.

Tonight, as the frontal system progresses eastward bringing the elevated thunderstorms into Cape Breton and begin approaching Southern Newfoundland. Additionally, behind the frontal system there is expected to be a clearing in behind the system allowing for instability to approach New Brunswick allowing for further convection to occur. Thunderstorms in the clearing are expected to start off as surface based showers and becoming elevated overnight. This instability mixed with cloud-top cooling is expected to give rise to elevated thunderstorms.

Tomorrow, the frontal system from overnight will continue to progress eastward and begin to slow down over Cape Breton and Southern Newfoundland. In behind the frontal system tomorrow there is likely to be a narrow corridor of MUCAPE nearing 700 J/Kg with shear of 20 to 30Kt giving rise to the possibility of thundershowers from Southeast New Brunswick into Central Nova Scotia.  

Wednesday, as the frontal system has departed and began to diminish over Newfoundland the previous couple of days rainfall is expected to give rise to excess moisture that align with Jet streak approaching from the West to act as a trigger for more severe thunderstorms over the interior of NB. There remains some uncertainty with this setup as it does rely on how must moisture gets injected into the interior of New Brunswick from these next couple of days. Current computer guidance is indicating that within the interior of New Brunswick there could be a risk of thunderstorm with gusts in excess of 80 km/h and hail nearing 2 cm. This come from MUCAPE nearing 2,000 J/Kg and MLCAPE nearing 1,000 J/Kg along with relatively good shear throughout the profile.

Thunderstorm Outlook for Today

Thunderstorm Outlook for Tonight

Thunderstorm Outlook for Tomorrow

Thunderstorm Outlook for Wednesday

Forecaster: McArthur/Lambert

 

 

Convective Outlook Valid for Today, Tonight and Tomorrow

Regional Impacts

Today

NB: Risk of marginally severe thunderstorms over northwestern New Brunswick this afternoon capable of producing heavy downpours, strong winds, and some small hail.

NS/PEI/NFLD/LAB: None.

Tonight

NS: Slight chance of elevated thundershowers over southwestern Nova Scotia before morning.

NB: Chance of a few thundershowers over northern New Brunswick with locally heavy downpours.

PEI/NFLD/LAB: None.

Tomorrow

NS: Slight chance of some isolated embedded thundershowers over mainland Nova Scotia.

NB: Slight chance of an isolated thundershower over extreme northwestern New Brunswick.

PEI/NFLD/LAB: None

 

Convective Discussion…

An active couple of days are in store for Atlantic Canada as a trough approaches from the west and begins to erode a ridge of high pressure over the central Maritimes. Today, the main threat area will be in parts of northwestern New Brunswick, where some marginally severe thunderstorms are possible this afternoon. Some overnight convection is lingering over the area of interest, leading to some increased cloud cover, but current satellite imagery shows clearing off to the west over southern Quebec. This should allow MLCAPE values to rise near 1000 J/kg this afternoon over the northwestern portion of New Brunswick and with effective shear near 40 knots, some marginally severe thunderstorms are possible. One limiting factor in the intensity of these storms will be relatively moderate lapse rates, but given enough clearing early this afternoon, storms should have no issues firing. Given the weaker lapse rates, hail will not be much of a concern, but some decent PWAT values near 30 to 35 mm will lead to some heavy downpours in thunderstorms. In addition, there is potential for some strong wind gusts in the downdrafts of these storms. Without the 12Z sounding out of Caribou this morning, there isn’t a good sample of the current environment over the area, but the Maniwaka sounding from 00Z last night shows a relatively unstable airmass in a highly sheared environment. In addition, model tephigrams are indicating some curvature in the low level winds over northwestern New Brunswick this afternoon leading to a non-zero tornado risk, though this risk remains very low at this time. Severe thunderstorm watches may be issued early this afternoon as confidence increases.

Tonight, the trough will continue to slowly move east, reaching southwestern Nova Scotia by morning. With some weak mid-level instability expected overnight, some elevated thundershowers are possible here, in addition to northern New Brunswick. The trough will continue to move east through the day tomorrow, extending the risk for an elevated thundershower over parts of mainland Nova Scotia. The unstable airmass behind the trough may also lead to some isolated thundershowers over extreme northwestern New Brunswick in the afternoon.

 

Thunderstorm Outlook for Today

Thunderstorm Outlook for Tonight

Thunderstorm Outlook for Tomorrow

Forecaster: Copp