Convective Outlook Valid for Today , Tonight and Tomorrow

Regional Impacts

Today:

Lab: Risk of a thundershower giving moderate wind gusts and rainfall rates.

NL: Risk of a thundershower giving moderate wind and rainfall rates, along the southern coasts.

NS: Risk of a thundershower inland.

NB/PEI: NIL.

Tonight:

Lab: Risk of a thundershower giving moderate wind gusts and rainfall rates.

NS/NB/PEI/NL: NIL.

Tomorrow:

Lab: Risk of isolated thundershowers giving moderate wind gusts and heavy rainfall.

NS/NB/PEI/NL: NIL.

Convective Discussion

The low-pressure system from yesterday is currently located to the southeast of Nova Scotia. This system is still giving embedded showers and thundershowers with isolated cells giving rainfall rates near 25 mm/hr. As this system progresses, model guidance is indicating that a lot of the forcing will diminish throughout the day. However, there is a cool trough that is forecast to move through the Maritimes, which will mainly act as a trigger for isolated thundershowers over mainland Nova Scotia; predominant areas of concern would be the higher terrain. Over Labrador, there is a decaying ridge of high pressure, and looking at satellite imagery, there is a clearing of mid to upper-level cloud along with a burning off of mist throughout much of the region. CAPE values are rising to near 1,000 J/kg because of this clearing trend. Daytime heating will act as a trigger and initiate some isolated thundershowers.

Tonight into tomorrow, a frontal system will approach Labrador from Northern Quebec today and affect Labrador tonight into tomorrow. There are some timings issues for this frontal system as it approaches, as such hazards are on the lower side. If the system progresses slower and maintains intensity, then tonight there is less confidence in thundershowers tonight and hazards could be more intense for the tomorrow period. Current guidance is giving an early afternoon of approximately 1,500 J/kg of Mixed Layer CAPE (MLCAPE) with shear values remaining around 15KT. If this system moves slower than it will be more likely that the jets will move through at a more effective timing, allowing shear to increase, which would lead to better organization of convection.

Thunderstorm Outlook for Today

Thunderstorm Outlook for Tonight

Thunderstorm Outlook for Tomorrow

Forecaster: Lambert

Convective Outlook Valid for Today , Tonight and Tomorrow

Regional Impacts

Today:

NS/NB/PEI: Risk of thunderstorms giving moderate wind and heavy downpours.

Lab: Risk of thundershowers.

NL: Nil.

Tonight:

NS/ PEI: Risk of thunderstorms giving heavy downpours.

Lab: Risk of thundershowers, mainly over higher terrain.

NB/NL: Nil

Tomorrow:

Lab: Risk of thunderstorms giving moderate wind, heavy downpours and a risk of small hail.

NL: Risk of thunderstorms along the southwest coast.

NS: Risk of a thundershower.

NB/PEI: Nil

Convective Discussion

A Low off the southwest coast of Nova Scotia is having its frontal wave sheared apart, which is allowing for a complex setup for today and into tomorrow. Looking at water vapour imagery, along with upper-air soundings, we can see that the main cold front is back towards the US Eastern Seaboard; meanwhile, the upper jets have sheared off from the low centre as the trowel wraps through Nova Scotia and New Brunswick, creating a dry slot. Along with the synoptic setup, there is vorticity advection affecting Northwest New Brunswick, and a departing ridge over Labrador, which is allowing for topography-induced troughs to develop. With this setup, we are seeing Precipitable Water values (PWAT) nearing 50mm, along with CAPE values hovering around the 500 J/kg mark. As such, going forward with this setup, it is most reasonable to use the Most Unstable CAPE (MUCAPE) values, to which we are seeing a swath of MUCAPE values between 500-1000 J/Kg around the Maritimes and Labrador.

Tonight, the disconnected frontal wave from today will progress eastward, allowing for some isolated thunderstorms to persist in the overnight hours for the Maritimes. For Labrador, there is a risk of thundershowers overnight; This drier air could allow for some thunderstorms overnight, though there is more uncertainty with this.

Tomorrow, remnants from today’s frontal wave will likely stay just to the southwest of Newfoundland, and model guidance indicates that convection will struggle to move inland. For Labrador, there is a stronger low-pressure system moving through Northern Quebec and Southern Baffin Island, which model guidance suggests a cold front could extend from Ungava Bay to Southern Quebec. The warm sector will enter Labrador with this frontal system, bringing a slight risk of hail, moderate winds, and rainfall. As this system progresses, the risks could change, as there are some timing uncertainties.

Thunderstorm Outlook for Today

Thunderstorm Outlook for Tonight

Thunderstorm Outlook for Tomorrow

Forecaster: Lambert

Convective Outlook Valid for Today , Tonight and Tomorrow

Regional Impacts

Labrador… Risk of thunderstorms today across western and central areas – may approach severe limits briefly in the Churchill Falls area today with gusty winds and heavy downpours.

Nova Scotia…  Chance of thundershowers in the overnight tonight with shower activity arriving from the SW. This risk extends eastwards in the day on Thursday. Moderate rainfall is the only hazard being forecast over land areas.

New Brunswick… Risk of an isolated thunderstorm near the Quebec border in the afternoon on Thursday.

Convective Discussion

The synoptic pattern is slowly advancing to the east in the next 24 to 48hrs. This brings a change in the weather across the Maritimes.

Ample surface moisture is in place today(dew points near 19), and effective shear(30kts) in the vicinity of the 2 forcings is good. The delay in anything getting going is simply the pace of the trigger itself. In Labrador, the trof will spark up this afternoon and may bring gusty winds and decent downpours. Small hail is also possible but shouldn’t exceed 1.5cm. Offshore from NS over the southwestern marine district, severe storms are possible and may form a decent line bringing gusts to near 90km/h. This will be monitored in case Squall watches or Warnings are required (depicted in yellow). As the low continues to wrap further and slowly advance east tonight, the thundershower risk moves into Nova Scotia. But it is forecast to be embedded in the overall greater shower activity (depicted in grey). It’s very warm at 700mb and quite dry in the upper levels this morning(Yarmouth sounding). Going to take some time to moisten the entire column to support any lightning activity. By tomorrow afternoon, the 100kt southerly jet at 250mb is just east of Halifax and situated as such that severe weather is not being forecast over any land areas. The orientation is not conducive this time.

Thunderstorm Outlook for Today

Thunderstorm Outlook for Tonight

Thunderstorm Outlook for Tomorrow

Forecaster: Tirone.

Convective Outlook Valid for Today , Tonight and Tomorrow

Regional Impacts

Labrador… Risk of thunderstorms today and tomorrow, with heavy downpours and some gusty winds possible.

Newfoundland… Risk of thunderstorms across eastern Newfoundland today, with some heavier downpours and frequent lightning possible.

PEI… Slight risk of thunderstorms today.

Nova Scotia…  Slight risk of thunderstorms today, mainly across eastern areas.

New Brunswick… Risk of isolated thunderstorms, mainly over northwestern sections late in the day.

 

Convective Discussion

The region currently remains under a somewhat anomalous pattern characterized by weak blocking. Most of the Maritimes lie between a trough extending from the Great Lakes northward into Labrador and a slow-moving low-pressure system approaching the Avalon Peninsula. This pattern is resulting in generally weak steering flow and a continued focus for convective development across portions of the region.

Across Labrador, conditions are expected to remain much the same as they were yesterday, although vertical motion may be slightly weaker. CAPE values in the 500 to 1000 J/kg range, combined with moderate low-level shear, will continue to support fairly widespread convection through the afternoon and evening. Rainfall rates in the strongest storms will likely reach 15 to 20 mm/h.

The low-pressure system over the marine area south of Newfoundland has transported more moisture into eastern portions of the Maritimes than previously anticipated. This increase in moisture has raised the potential for showers and thunderstorms in areas where low-level convergence is sufficient to overcome existing convective inhibition. However, with the exception of eastern Newfoundland, the shear profile across the region is generally not supportive of severe thunderstorms. As a result, most convection is expected to be relatively weak and disorganized, with only a low risk of severe weather. Nevertheless, locally heavy downpours remain possible where thunderstorms are able to develop.

Over eastern Newfoundland, the combination of stronger forcing associated with the nearby low-pressure system and somewhat more favourable wind profiles will support more organized convection. The most likely scenario remains clusters of thunderstorms capable of producing frequent lightning and locally heavy rainfall, with rainfall rates of 15 to 25 mm/h possible in the strongest cells. Strong downdrafts and hail are not expected to be significant concerns at this time.

Thunderstorm Outlook for Today

Thunderstorm Outlook for Tonight

Thunderstorm Outlook for Tomorrow

 

Mel Lemmon

Convective Outlook Valid for Today , Tonight and Tomorrow

Regional Impacts

Labrador… Risk of thunderstorms with downpours and small hail possible, today and tomorrow.

Newfoundland… Risk of elevated thunderstorms tomorrow with some heavier downpours.

PEI, NS… No Risk of thunderstorms.

New Brunswick… Risk of thunderstorms northwest tomorrow.

Convective Discussion

A surface trough will continue to move across Labrador today shifting slightly farther east tomorrow, with moderate instability developing during the afternoon. CAPE values are forecast to be in the 500 to 1000 J/kg range, while strong low-level winds will provide support for organized convection where thunderstorms are able to develop.

Scattered thunderstorms are expected along and ahead of the trough this afternoon and this evening. Rainfall rates could reach 15 to 20 mm/h, although the progressive nature of the storms should limit the duration of heavy rainfall at any one location.

While severe weather is not anticipated, some storms may become organized into short line segments or a convective complex. Should this occur, locally heavier rain and some gustier winds are possible.

Across eastern Newfoundland, a low-pressure system tracking near the Avalon Peninsula will provide additional lift and support for elevated convection. While surface-based instability is expected to remain limited, elevated thunderstorms may develop within the broader area of precipitation associated with the system. The strongest thunderstorms over eastern Newfoundland will be capable of producing brief periods of heavy rain, with rainfall rates of 15 to 25 mm/h 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

Labrador… Risk of thunderstorms with downpours and small hail possible, today and tomorrow.

Newfoundland, PEI, NS… No Risk of thunderstorms.

New Brunswick… Risk of thunderstorms just north of province.

Convective Discussion

A ridge of high pressure over eastern Atlantic Canada will suppress convection across much of the region. Over the next couple of days, this ridge will gradually shift east, allowing an area of low pressure to move slowly across the remainder of the region. There is some potential for deeper convection just ahead of the low and its associated surface trough over Labrador, both today and tomorrow.

For Labrador, surface-based CAPE values between 500 and 1000 J/kg today and tomorrow will provide sufficient instability for thunderstorm development. Today, however, the triggering mechanism will be subtle. By tomorrow, a surface trough will provide a more focused trigger along with slightly higher low-level moisture. As a result, locally heavy downpours and small hail will become somewhat more likely ahead of this feature. Deep-layer shear is moderate, while low-level shear of around 20 knots may be sufficient to organize convection into a line or possibly support training thunderstorms.

Thunderstorm Outlook for Today

Thunderstorm Outlook for Tonight

Thunderstorm Outlook for Tomorrow

 

Mel Lemmon

Convective Outlook Valid for Today , Tonight and Tomorrow

Regional Impacts

Today

Lab: Risk of thunderstorms near noon and later today over western sections.

Northern NB: Risk of a TCU or very brief isolated thundershower later today.

Offshore and over the Avalon: Embedded convection is ongoing and remains possible today.

Tonight

Thundershower activity is not forecast over land areas tonight.

Tomorrow

Lab: Thunderstorm risk expands further north and east along the shifting frontal boundary.

Coastline of Nova Scotia: Embedded thundershower risk circles around the offshore low and may approach the Atlantic coast late in the day (prog goes until midnight). Not forecasting anything severe at this time.

Convective Discussion

Atlantic Canada finds itself sandwiched between 2 elongated frontal boundaries this weekend. One is offshore and stretches from the Grand Banks to the Carolinas. The second is situated from Ungava Bay back to eastern Lake Superior. It is easy to see the forcings on the 500mb charts, but additionally the cloud field on satellite is quite pronounced this morning. These long wave troughs are the lifting mechanisms for any convection that occurs in the next 24 to 48-hrs. Moisture is ok, but shear is substantially lacking in NB. Labrador is a different story. Shear may actually be too great for the amount of lift available. That being said, if an organized cell can form tomorrow, gusty winds (of 60 to 70 km/h) nearby could be a factor at play. This will be monitored. **Also of note is the forest fire smoke that is still affecting some areas of central Quebec. This could act as CIN that the models are not accounting for.

Thunderstorm Outlook for Today

Thunderstorm Outlook for Tonight

Thunderstorm Outlook for Tomorrow

Forecaster: Tirone.

Convective Outlook Valid for Today , Tonight and Tomorrow

Regional Impacts

Today

Lab: Risk of non-severe thundershowers.

NL: Risk of embedded thundershowers over the Avalon, bringing moderate (to at times potentially heavy) rainfall.

Tonight

Thundershower activity pushes out over the eastern marine domain.

Tomorrow

Lab: Thunderstorms are possible over western sections.

NB: There is a risk of thunderstorms developing in the afternoon over central and northern areas.

Convective Discussion

An elongated frontal boundary continues to affect the eastern parts of Nfld today giving a chance of embedded thundershowers. The potential hazard here is moderate to heavy rainfall in convective burts. Pwats on St. John’s sounding this morning is 39, showing the airmasses’ tropical nature. This forcing will slump over the eastern marine domain tonight, marked in broad grey. There is a secondary forcing across Labrador and the Quebec Lower North Shore that will act as a TCU/CB trigger this afternoon. These storms are not expected to reach severe limits – CAPE is 500-750J/kg, effective shear 15-25kts. Isolated lightning is the main hazard. This trof is the forcing for Day 2 in NB.

Thunderstorm Outlook for Today

Thunderstorm Outlook for Tonight

Thunderstorm Outlook for Tomorrow

Forecaster: Tirone.

Convective Outlook Valid for Today , Tonight and Tomorrow

Regional Impacts

Today

Lab: Risk of a thundershower.

NS/NL: Risk of a thundershower near the Atlantic Coast.

NB/PEI: Nil

Tonight

NS/NB/PEI/NL/LAB : Nil

Tomorrow

NS/NB/PEI/NL/LAB : Nil

Convective Discussion

The frontal system from yesterday is currently over Northern Quebec. Based on a combination of Water Vapour imagery and observation analysis, the frontal system is beginning to decay, which is progressing it toward a closed-off low-pressure system. As a result, enough remnant forcing remains over Labrador to give rise to isolated thundershowers today, specifically along the Northeastern coast. For the remaining parts of the Maritimes and Newfoundland, the decaying frontal wave is allowing moisture to flow in from the US, likely due to spillover from TS Betha and a building ridge over the Northeast USA. Because of this setup, the plume of moisture and its convective properties can shift with the position of the ridge axis, as well as with how the synoptic setup progresses. Within this plume of moisture, models are indicating CAPE values over 1,500 J/Kg with effective shear values of 30-40KT. One thing to note, however, is that it was intentional to leave the grey region over the Atlantic predominantly off the coast; high-resolution guidance indicates a struggle to push convection inland, while the regional model indicates that convection could move inland. Based on the synoptic setup, it was a conscious effort to go with the high-resolution guidance. 

Thunderstorm Outlook for Today

Thunderstorm Outlook for Tonight

Thunderstorm Outlook for Tomorrow

Forecaster: Lambert

Convective Outlook Valid for Today , Tonight and Tomorrow

Regional Impacts

Today

NB: Risk of Severe thunderstorms with heavy downpours, small to moderate sized hail, strong wind gusts. Risk of  a tornado over Northwestern sections.

PEI/NS: Risk of a thundershower.

NL: Risk of a thundershower over southeastern sections of the island.

LAB: Nil.

Tonight

Lab: Risk of a thundershower over central sections.

NL: Risk of a thundershower over Southern and Southeastern sections of the island.

NB/PEI/NS : Nil

Tomorrow 

NS/PEI/NL /Lab : Risk of a thundershower.

NB: Nil.

Convective Discussion

A frontal system near the Hudson Bay is progressing east and is the initiation forcing for the convection expected today. Currently, we have significant moisture across the Maritimes, along with curved jets moving through the US Eastern Seaboard. The frontal system, paired with these jets and ample moisture, with a cooler/drying airmass behind the cold front, is allowing for there to be a risk for severe thunderstorms in Northwestern NB, with the risk of a tornado today. This setup is giving Mixed Layer CAPE (MLCAPE) values near 1500 J/kg with Most Unstable CAPE (MUCAPE) exceeding 2,000 J/kg along the NB/Maine boarder. Additionally with this amount of instability, and the jet structure previously mentioned, we have a significant amount of Shear and Helicity. Looking at Convective model soundings we are seeing a Cloud Layer shear near 70 Knots, with Storm Relative Helicity (SRH) within the Surface to 3km nearing 140 m2s2. All of these properties do give rise to the possibility of supercells in Northwestern New Brunswick. As such when considering supercells the bunkers right movement seems the most reasonable, which is also fairly aligned with the mean wind direction (generally a Northeast direction).

As the frontal system progresses through Atlantic Canada tonight, we are expected to see a slight weakening in the jet structure and frontal boundaries. As such, there remains a risk for thunderstorms through central Labrador and near the Atlantic Coast. Model guidance does want to push convection onshore but the problem becomes that with the weakening forcings, making the land-sea transition during the overnight hours will be a struggle.

Tomorrow, the synoptic setup becomes more difficult for model guidance to capture the thunderstorm risk; as such, the regions in grey are likely to change as we move closer to the valid timeframe. The synoptic setup is that the low progressing through Atlantic Canada today has the possibility of getting stalled over Labrador with a building ridge over the continental US, and the Azores high. This setup has models indicating a potential Atmospheric river coming from the Gulf of Mexico into Atlantic Canada. As this setup requires several conditions, some of which there is low to moderate confidence in occurring, this is the justification for the grey region not having more details.

Thunderstorm Outlook for Today

Thunderstorm Outlook for Tonight

Thunderstorm Outlook for Tomorrow

 

Forecaster: Lambert

Convective Outlook Valid for Today , Tonight and Tomorrow

Regional Impacts

PEI.. Risk of thunderstorms tomorrow.

NB.. Risk of thunderstorms overnight, risk of severe thunderstorms for tomorrow.

NS.. Risk of thunderstorms overnight and tomorrow, heavy rainfall rates possible.

Newfoundland.. Risk of thunderstorms later tomorrow.

Labrador.. No thunderstorms expected.

Convective Discussion

Moisture will gradually increase across the region over the next 24 hours as a low-pressure system and associated deep upper trough, extending well into the eastern United States, slowly approach the Maritimes.

A plume of exceptionally high precipitable water is forecast to skim the Atlantic coast of Nova Scotia tomorrow morning before moving across eastern Nova Scotia early in the day and potentially affecting eastern Newfoundland later in the afternoon. Very heavy rainfall rates are possible within this plume, with rates likely exceeding 30 mm/h at times. While the plume may linger near the coast for much of the day, it is currently expected to only briefly affect any given location, limiting storm-total rainfall amounts.

Across New Brunswick, moisture levels will be somewhat lower than over eastern Nova Scotia. However, stronger instability is expected to develop ahead of the surface trough and approaching upper-level disturbance. Surface-based CAPE values are forecast to exceed 1000 J/kg, while deep-layer shear is expected to exceed 40 kt, supporting a risk of severe thunderstorms.

The shear profile appears relatively straight, favouring fast-moving thunderstorms and supercells. Storm motion is expected to be generally toward the northeast at approximately 50 km/h, allowing for both left- and right-moving supercells. These storms may produce small hail, strong wind gusts, and locally intense rainfall. Although rainfall rates could be high, the rapid storm motion should limit most rainfall totals to around 25 mm.

Thunderstorm Outlook for Today

Thunderstorm Outlook for Tonight

Thunderstorm Outlook for Tomorrow

Mel Lemmon

Convective Outlook Valid for Today , Tonight and Tomorrow

Regional Impacts

Labrador… low chance of a weak thunderstorm.

NS, PEI, NB, NFLD… no thunderstorms expected.

Convective Discussion

We are looking at a relatively dry and stable airmass for the next two days across most of the region. A low pressure system over Labrador, combined with some convergence and daytime heating, may be sufficient to produce a few lightning strikes. However, CAPE is very weak and shear is minimal, so there is no risk of significant impacts from thunderstorms.

By Wednesday, a low pressure system moving across Quebec will help bring more substantial low-level moisture into the region. There is a slight chance that severe thunderstorms could develop over New Brunswick, but with the event still three days away, there remains too much uncertainty to quantify the potential impacts. It is also possible that elevated convection could impact Nova Scotia and southern Newfoundland during this period with heavy rainfall. Tomorrow's guidance should provide a clearer outlook.

Thunderstorm Outlook for Today

 

Thunderstorm Outlook for Tonight

Thunderstorm Outlook for Tomorrow

 

Mel Lemmon

Convective Outlook Valid for Today, Tonight and Tomorrow

Regional Impacts

Today

NS/NL: Isolated embedded thundershowers giving strong wind gusts and heavy rainfall.

NB/PEI/LAB: None

Tonight

NL/LAB: Slight risk of an embedded thundershower.

NB/NS/PEI : None

Tomorrow

None

Convective Discussion

A low pressure system is tracking from the Gaspe Peninsula slowly northeastward to lie over Anticosti this evening then into south-central Labrador by tomorrow morning. Organized convection this morning had been primarily along the cold front across the southern Maritime waters south of Nova Scotia, but an isolated embedded thunderstorm is still possible today in the northern Gulf of St. Lawrence and southern Newfoundland today. With high precipitable water and upslope flow, heavy rainfall is expected across southern Newfoundland and the Lower North Shore of Quebec today. Closer to the low center is also an area where there could be sufficient lift to breach the warm 500 mb cap and support isolated strikes, furthering potential rainfall amounts. The cold front has produced strong wind gusts over Nova Scotia and the Maritimes waters thanks to a strong 850mb LLJ.

For tonight there is a risk of isolated thundershowers continuing east the low centre across southeastern Labrador, and along the cold front as it moves into the Grand Banks. The low centre slowly fills as it drifts northeastward tomorrow and eventually out into the Labrador Sea tomorrow evening. For tomorrow, there is a slight risk of a strike along the trowal axis east of the low centre as it moves into the Labrador Sea. Meanwhile, a ridge of high pressure moves into the Maritimes tomorrow afternoon.

Thunderstorm Outlook for Today

Thunderstorm Outlook for Tonight

Thunderstorm Outlook for Tomorrow

Convective Outlook Valid for Today, Tonight and Tomorrow

Regional Impacts

Today

LAB: chance of isolated thundershowers over eastern sections giving brief strong wind gusts.

NB: chance of embedded thunderstorms late evening over western sections.

NS/PEI/NL: None

Tonight

NS/NB/PEI: chance of embedded thunderstorms giving heavy rainfall and strong wind gusts.

Tomorrow

NS/NL/LAB: chance of embedded thunderstorms giving heavy rainfall and strong wind gusts.

NB/PEI: None

Convective Discussion

The stalled upper low over Labrador over the last few days is finally starting to track northward and weaken today. There is a weak shortwave currently over central Labrador, moving towards the east, and this is the trigger for thundershowers today. There is potential effective shear of 30-40kt and MLCAPE of 250J/kg, but with low moisture, some cells may organize and provide brief strong wind gusts.

While a ridge dominates the Maritimes and Newfoundland during the day, a low pressure system currently over the Great Lakes will deepen as it tracks towards the Maritimes tonight. Rain ahead with the warm front should reach New Brunswick this evening, while convective showers with the cold front will move across the Gulf of Maine and towards western New Brunswick and Nova Scotia close to midnight. This system is quite active this morning along the warm front, aided by strong dynamical forcing. Overall dynamics and thermodynamics are expected to be reduced as the system reaches the Maritimes. However, there is an increasing 60kt 850mb LLJ tonight ahead of the cold front in Nova Scotia and the southern Maritime waters. This along with possible mid-level cooling aloft may help embedded thunderstorms persist as the front continues eastward overnight, reaching eastern Nova Scotia by mid-morning. Regardless if lightning does persists, strong southerly winds and increasing precipitable water (40-50 mm) will allow for heavy rainfall rates and strong wind gusts with the frontal passage.

For tomorrow, the low centre is expected move from northern New Brunswick towards the northeast, reaching Anticosti by tomorrow evening. The cold front continues to advance, reaching Newfoundland by mid-morning. Embedded thunderstorms are still possible with heavy rain across southern Newfoundland.

Thunderstorm Outlook for Today

Thunderstorm Outlook for Tonight

Thunderstorm Outlook for Tomorrow

Convective Outlook Valid for Today, Tonight and Tomorrow

Regional Impacts

Today

Nfld: Chance of scattered non-severe thunderstorms near St. Anthony, and the Avalon.

Labrador: chance of isolated thundershowers in area marked in grey.

Tonight

No thunderstorms forecast in Atlantic Canada.

Tomorrow

Labrador: chance of isolated non-severe thundershowers over eastern sections.

Western Nova Scotia/Gulf of Maine: chance of scattered embedded thunderstorms along an advancing front very late in the day (near midnight into Sunday).

Convective Discussion

There is now dry air in place across the Maritime provinces. This will inhibit any organized convection today. Cu fields are expected to develop by noon, but will struggle to lift past even 700mb. NB is observing sfc dewpoints of just 8 this morning. A thermal ridge is located off to the west over New England.

Nfld is a bit of a different story synoptically. The remnants of a front is still effecting the Avalon and Grand Banks with a thunderstorm chance. And another hang-back trof is acting as a second trigger across southern Labrador and over the tip of the Northern Peninsula. These storms are not expected to reach warning criteria or approach severe limits today.

Weekend Setup: Day 2 brings in a more substantial organized TS risk very late in the day/overnight approaching the Maritimes from the west. Rainfall amounts look to be 25-40mm at this point for some areas of the Maritimes. The frontal passage is overnight Saturday into Sunday morning. This prog is only valid from the noon to midnight time period. Development is shown as grey in the Gulf of Maine.

Thunderstorm Outlook for Today

Thunderstorm Outlook for Tonight

Thunderstorm Outlook for Tomorrow

Forecaster: Tirone. 3:18:01 Jul 17 2026

60   FPCN11 CWHX 171354 FORECASTS FOR NOVA SCOTIA ISSUED   13:54:57 Jul 17 2

Convective Outlook Valid for Today, Tonight and Tomorrow

Regional Impacts

Today

NB/NS/PEI/NL: Risk of thunderstorms giving brief strong winds gusts, small hail and locally heavy downpours. Risk of higher gusts for southwestern New Brunswick and western Nova Scotia this evening.

Lab: Slight risk of a thundershower giving small hail.

Tonight

NL: Slight risk of a thundershower.

NB/PEI/NS/LAB: None

Tomorrow

None

Convective Discussion

An upper low over Labrador will remain stationary today while a quick moving shortwave trough will move from Quebec towards central Maine then southern New Brunswick and Nova Scotia late this afternoon and towards southern Newfoundland by the evening. There is the possibility of pop-up convection ahead of the trough this afternoon where much of the Maritimes is clear this morning, allowing convective temperatures to be reached, especially across PEI, eastern Nova Scotia and southwestern Newfoundland once clouds clear early this afternoon. With relatively dry dew points over the Maritimes under a westerly flow, precipitable water of 15 to 20 mm and relatively weak CAPE (500J/kg), thunderstorms that develop are expected to be non-severe.  However, with the trough, dynamics are most favoured in the exit region of a strong 250mb jet moving into southwestern New Brunswick and western Nova Scotia. This area may also see a slight increase in precipitable water and CAPE values in this area may exceed 750 J/kg and effective shear increasing to 50 kts based off Maniwaki and Gray 12Z soundings. Organization is possible with the main threats being strong wind gusts and small hail if a line develops. The risk of more elevated convection will continue tonight into Newfoundland. Under the low over Labrador, showers are expected with the risk of convection east of the low. CAPE is quite low but with very cold air aloft, small hail is possible.

For tomorrow, the upper low will slowly make its way eastward by the evening. Other than continued scattered showers with the upper low, the risk of convection at this time is low.

Thunderstorm Outlook for Today

Thunderstorm Outlook for Tonight

Thunderstorm Outlook for Tomorrow

Convective Outlook Valid for Today, Tonight and Tomorrow

Regional Impacts

Today:

NB/NS/PEI/NL: Risk of thunderstorms giving strong wind gusts, small hail and brief heavy downpours.

LAB: Risk of thunderstorms giving small hail.

Tomorrow

NB/NS/PEI/NL: Risk of a thundershower giving strong winds gusts and small hail.

LAB: Risk of a thundershower giving small hail.

Convective Discussion

An upper low over Labrador will become stacked today while a cold front continues across southeastern Labrador, Newfoundland and exits south of Nova Scotia this morning. While high level smoke prevented much of the anticipated convection yesterday, convection has been able to fire across southeastern New Brunswick, PEI and Newfoundland this morning where the smoke has cleared. Elevated convection across Newfoundland and the Maritimes marine waters south of Nova Scotia is also on the go this morning with the help of a 45kt low to mid level jet and a favourable upper jet. With dewpoints in the mid to high teens and precipitable water of 30-35, there is the risk of heavy downpours and possible small hail.  East of the low, sufficient lift will aid in thunderstorms continuing across eastern Newfoundland and southeastern Labrador.  Mixed CAPE of upwards of 750 J/kg and effective shear of 20 to 30 kt will allow convection to sustain.

Daytime heating with clearing skies and cooler air aloft will aid in the potential for convection continuing across eastern Nova Scotia, the southern Gulf of St. Lawrence and into central Newfoundland by the afternoon. Mixed CAPE may reach upwards of 1500 J/kg and with effective shear of 40 kt, cells that develop may organize into lines, with a small risk a supercell with sufficient low level helicity this morning. The drier air aloft entering from New Brunswick could lead to brief strong wind gusts in pop up convection across northern New Brunswick later this afternoon.

For tomorrow, a short wave trough from Quebec will track into New Brunswick and across the Maritimes in the afternoon. With relatively dry dew points still in the area under a west-northwest flow and reduced CAPE (500J/kg), the main threats will whatever develops will be brief strong wind gusts and small hail.

Thunderstorm Outlook for Today

Thunderstorm Outlook for Tonight

Thunderstorm Outlook for Tomorrow