Convective Outlook Valid for Today , Tonight and Tomorrow

Regional Impacts

Today

NFLD: Slight chance for isolated thundershowers.

NS/PEI/NB/LAB: Nil.

Tonight

NS/PEI/NB/NFLD/LAB: Nil.

Tomorrow

NS/PEI/NB/NFLD/LAB: Nil.

Convective Discussion

The cool trough from yesterday continues to progress through Atlantic Canada. Looking at water vapour imagery, we can see that a shortwave has started interacting with some of the remnant baroclinicity in the area, allowing for a shallow low to develop over the southern Marine districts. However, due to the synoptic setup this low is being quickly cut off from upper level support while additional short waves with surface reflections are moving to interact with this low over the southern marine district. With these interactions and that there is building heights over Atlantic Canada the risk for thunderstorms will dissipate throughout the day.

With these rising heights and a dominant high over the region, there is no thunderstorms forecast for tonight nor tomorrow (Tuesday September 1, 2026).

Please note that this is the final scheduled outlook and discussion for the Atlantic Region this year. Subsequent updates will be issued on an as needed basis.

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/PEI: Slight chance for isolated thunderstorm(s). Hazards: 70 km/h wind gusts; 0-1 cm hail; 15-25 mm rainfall.

LAB: Slight chance for isolated thundershower(s).

NS/NFLD: Nil.

Tonight

PEI/NS/NFLD: Chance for isolated thundershower(s). Hazards: 70 km/h wind gusts; 15-25 mm rainfall.

NB/LAB: Nil.

Tomorrow

NFLD: Slight chance for isolated thundershower(s).

NS/PEI/NB/LAB: Nil.

Convective Discussion

Looking at today's surface analysis, there is a low off the coast of Labrador along with a cold upper low over Northern Quebec into Labrador. Additionally with this setup we have two significantly strong curved jets, a 55KT jet at 500mb and a 95KT jet over northern New Brunswick. As the cold upper low progresses to the south with these jets, we can expect to see some isolated thunderstorms in New Brunswick, western PEI, and Southeastern Labrador. Looking at Surface based CAPE, we are seeing CAPE values remain mainly around 700 J/Kg with some isolated areas over NB and PEI reaching 1,000 J/Kg, over these areas we do have Effective Shear reaching 30 to 35Kt over most of NB and PEI.

With the progression of this system sweeping through the Maritimes and Newfoundland there is guidance to suggest that overnight thundershowers are possible over eastern PEI, Nova Scotia, and Eastern Newfoundland. It is worth noting that in this outlook we have a region "B" this is to denote the possibility of waterspouts. As the system moves over Nova Scotia, guidance is suggesting that it could develop into a squall line which if that occurs there is a possibility that waterspouts could develop. Overnight Most Unstable CAPE (MUCAPE) values are expected to stay within the range of 500 J/Kg, except over warm waters where they could approach the 1,000 J/Kg mark. Additionally shear values are still expected to remain near 30Kt over warm waters but reduce down to 20Kt over land.

Tomorrow will begin a relatively quiet period as this system should depart eastern Newfoundland early into the valid period of the outlook. Once this system had departed a ridge is expected to develop over most of Atlantic Canada.

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

LAB: Scattered thunderstorms.

NS/NFLD: A chance of thundershowers.

NB/PEI: None.

 

Tonight

NS/NB/PEI/NFLD/LAB: None.

 

Sunday

NB/LAB: A chance of thundershowers.

NS/PEI/NFLD: None.

 

Convective Discussion

Over eastern Labrador today, a tropical moisture feed is expected ahead of a broad upper low and surface trough. This same system gave copious amounts of rain and gusty winds to parts of New Brunswick and Prince Edward Island yesterday. CAPE values near 1000 J/kg and effective shear of 30 to 40 knots are expected. While wind gusts and hail are possible, it will be training thunderstorms giving copious amounts of rain that is the main concern. Due to much lower CAPE values, the trough will give just a chance of thundershowers for parts of Newfoundland and eastern Nova Scotia. On Sunday an approaching trough will give a chance of thundershowers for northern New Brunswick and southeastern Labrador.

Thunderstorm Outlook for Today

Thunderstorm Outlook for Tonight

Thunderstorm Outlook for Tomorrow

 

Convective Outlook Valid for Today, Tonight and Tomorrow

Regional Impacts

Today

 

NB: Potential for severe thunderstorms giving strong wind gusts, small hail, locally heavy rainfall and slight risk of a tornado.

 

NS/PEI/LAB: Chance of isolated thundershowers giving local heavy rainfall.

 

NL: None.

Tonight

NB/PEI/NS/LAB: Isolated thunderstorms giving locally heavy rainfall.

NL: None

Tomorrow

NL/LAB: Scattered thunderstorms giving brief strong wind gusts, small hail and locally heavy downpours.

NS/PEI : Isolated thundershowers.

NB: None

Convective Discussion

A stationary upper low sits over Hudson Bay, with a cold front that will progress eastward today across Maine and into New Brunswick by late this afternoon. Ahead of the front this morning, showers and embedded isolated thundershowers have persisted across northeastern New Brunswick, with some clearing expected early this afternoon prior to the cold front. This should allow for enough daytime heating for MLCAPE values to reach of exceed 1250 J/kg across central and western New Brunswick. With stronger southwesterly winds increasing with the approaching front, effective shear may reach 40 kt, with some indications of moderate low-level shear and storm relative helicity, storms that develop may either organize into lines or possible supercells with the risk of a tornado ahead or along the front. There is also an increasing 250mb jet moving into the Maritimes, and in an ideal left exit region, allowing for divergence aloft and the maintenance of storms. The main hazards will be strong wind gusts of 90 km/h, hail of 1-2cm and heavy downpours with rainfall rates of 30-40 mm/h possible.  The front extends also into southwestern and southcentral Labrador with possible isolated embedded thunderstorms.

A short-wave trough is also moving across the southern Maritimes marine district and some interaction with this system, possible clearing skies in the western Nova Scotia and the cold front may help with potential storm development also along the Bay of Fundy extending northeastward into Prince Edward Island late this afternoon and evening. Heavy downpours are the likely main threat with these given the orientation of storm development and possible training storms.

With an increasing 250mb jet spreading into the Maritimes tonight, storms may persist overnight across southeastern New Brunswick, Prince Edward Island and central Labrador giving heavy downpours.

For tomorrow, the cold front continues into eastern Labrador and Newfoundland while the shortwave moves across the eastern Maritimes marine waters and across southeastern Newfoundland with convection. There will be the risk of brief strong wind gusts, small hail and locally heavy downpours.

Thunderstorm Outlook for Today

Thunderstorm Outlook for Tonight

Thunderstorm Outlook for Tomorrow

Forecaster: McArthur

Convective Outlook Valid for Today , Tonight and Tomorrow

Regional Impacts

 

Today

 

NB: Chance for an isolated thundershower.

 

LAB: Slight chance for an isolated thundershower.

 

NS/PEI/NB/NFLD: Nil.

 

Tonight

 

NB: Chance for isolated thundershowers.

 

NS/PEI/NFLD/LAB: Nil.

 

Tomorrow

 

NB: Likely chance for severe thunderstorms. Most significant hazards: a possible tornado; 1-2 cm hail.

 

NS/PEI/LAB: Likely chance for isolated thundershowers.

 

NFLD: Nil.

 

Convective Discussion

 

After an active upper trough moved through Atlantic Canada, today is expected to be relatively quiet as a ridging is in place over most of the Atlantic provinces. There is however a progressing frontal system moving through Quebec which is giving some short waves passing through Labrador today with enough jet support to have Effective shear values nearing 25KT which could support some isolated thunderstorms is they form. For New Brunswick, there is the chance that prefrontal thundershowers form over the extreme Northwestern sections of the province. But they are currently not expected to become severe.

 

Overnight with the approaching frontal system from Quebec there is the chance of isolated thundershowers off the southern Coast of New Brunswick and Nova Scotia which could drift inland over New Brunswick.

 

Tomorrow, the frontal wave is sweeping through the Maritimes giving a collection of ingredients for severe thunderstorms to have a chance at forming. As the cold front progresses through the Maritimes, effective shear values are expecting to be near 40KT along with having a classically curved hodograph and ample low-level helicity it is possible that a tornado or two could form tomorrow. Additionally, looking at soundings the risk for hail is likely to be near 1-2cm. It is worth noting that some sounding analogues do indicate over 2cm of hail, so it is something to keep in mind for tomorrow, but it does appear unlikely to have hail this significant.

 

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/PEI/NB: Likely for scattered thunderstorms. Hazards: 50-70 km/h wind gusts; 0-1 cm hail; 20-40 mm rainfall.

 

NFLD: Chance for isolated thundershower(s). Hazards: 15-25 km/h wind gusts.

 

LAB: Slight chance for isolated thundershower(s).

 

Tonight

 

NB/NS/PEI/NL/LAB: No thunderstorm risk expected.

 

Tomorrow

 

NB: Chance for isolated thunderstorm(s) over Northwestern NB.

 

NS/PEI/NFLD/LAB: Nil.

 

Convective Discussion

 

Today's surface analysis shows that there is predominantly an upper trough over the Maritimes which will act as a trigger for convection today. The most significant hazard is expected to be rainfall rates approaching 40mm/hr. This is largely due to the high PWAT's near 35mm still in play over most of the Atlantic Provinces. For Newfoundland and Labrador, there remains the same synoptic setup however there is expected to be a degradation in both trough strength and PWAT's over the island of Newfoundland. Over the Maritimes, specifically in the regions under the “B” location can see CAPE values nearing 1200 J/Kg meanwhile in Newfoundland, specifically in the southwest can also see CAPE values nearing 1000 J/Kg. Within this trough on the Eastern side of the trough there is jet support at the 500mb level nearing 40Kt and at the 250mb there is a stronger jet nearing 100Kt. On the western side of the trough there is a similar jet support at the 500mb level though at the 250mb level the jet drops down to a modest 60Kt.

 

As the trough passes through tonight, slight ridging is expected to build in, this combined with a fast approaching nighttime there is no convection anticipated over the Atlantic provinces.

 

An approaching cold front that is currently over Lake Superior, is expected to start impacting Northwest New Brunswick late in the day on Thursday. There is some uncertainty with the timing currently, but previous outlooks have indicated that there is a potential for strong winds and hail with this front. The area in Grey is given this as the timing uncertainty would cause a large variance in what is and is not possible during the designated timeframes.

 

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/LAB: Scattered thunderstorms.

NFLD: A chance of embedded thundershowers.

 

Tonight

NFLD: A chance of embedded thundershowers.

NS/NB/PEI/LAB: None.

 

Wednesday

NS/PEI: Scattered thundershowers.

NFLD/LAB: A chance of thundershowers.

NB: None.

 

Convective Discussion

The tropical moisture feed ahead of a broad upper low approaching New Brunswick will continue over most of Atlantic Canada today. Over Newfoundland there is a chance of embedded convection and synoptic warnings and statements are already in effect there. Clearing skies elsewhere will allow surface based convection. The area of most concern today is over portions of Nova Scotia, New Brunswick and PEI where CAPE values of 1000-1500 J/kg and effective shear near 30 knots are expected. An upper level jet may also contribute with the development but that is east of the main area of concern. While wind gusts and hail are possible, once again it will be training thunderstorms giving copious amounts of rain that is the main concern. On Wednesday, the upper low and afternoon destabilization will move over the eastern Maritimes and into southwestern Newfoundland. Conditions similar to today are expected but the shear will be a bit less so more muted impacts are likely.

Thunderstorm Outlook for Today

Thunderstorm Outlook for Tonight

 Thunderstorm Outlook for Tomorrow

Convective Outlook Valid for Today , Tonight and Tomorrow

Regional Impacts

 

Today

NS/NB/PEI/NFLD/LAB: A chance of thundershowers.

 

Tonight

NS/NFLD: A chance of thundershowers.

NB/PEI/LAB: None.

 

Tuesday

NS/NB/PEI/NFLD/LAB: A chance of thundershowers .

 

Convective Discussion

The tropical moisture feed ahead of a broad upper low over southern Quebec will continue over portions of eastern Nova Scotia, Prince Edward Island and Newfoundland today. Precipitation amounts are highly variable but anywhere within that area could receive significant amounts as rainfall rates approach 25 mm/hr at times or higher. Over northern New Brunswick clearing has occurred and surface based convection is possible this afternoon. MLCAPE values are expected to be 500-750 J/kg and the effective shear will be near 30 knots. Do to the limited CAPE, severe thundershowers are not expected however gusty winds, small hail and downpours are still possible.  On Tuesday, the tropical moisture feed and embedded thundershowers will persist over eastern Cape Breton and Newfoundland. Skies will be clearing elsewhere in the Maritimes as the upper low tracks across New Brunswick. MLCAPE values of 500-750 J/kg and effective shear near 30 knots are expected once again so a repeat again of the conditions forecast for northern New Brunswick today.

Thunderstorm Outlook for Today

Thunderstorm Outlook for Tonight

Thunderstorm Outlook for Tomorrow

 

Convective Outlook Valid for Today , Tonight and Tomorrow

Regional Impacts

 

Today

Maritimes: Embedded thunderstorms within the greater rainfall area bringing enhanced rainfall rates and totals. The main hazard is very heavy downpours, and potentially training storms.

 

Tonight/Tmrw Morning

Ongoing moderate to heavy rain shower activity with embedded thundershowers advances across the Gulf of St. Lawrence and to the southern part of Nfld.

 

Monday

Atlantic Canada: Widespread risk of thundershowers in the large scale synoptic flow. Local torrential downpours remain the main concern, enhanced further by any repetitive thunderstorms. Clearing begins from west to east into Tuesday.

 

Convective Discussion

Rain is the name of the game today. A strong moisture feed has developed into the Maritimes stemming all the way from Florida. This is very evident on water vapour imagery this morning. This morning’s soundings also show a completely saturated column. Pwats are near 60, and observed dew points of 20. Synoptic rainfall warnings and special weather statements are already in effect. If embedded thunderstorms train over one specific area, or rates exceed 25 mm/h, thunderstorm warnings will also be used for the local area to describe the hazard/risk further. This weather event is forecast to continue into Monday for the Maritimes, and begin affecting Nfld in the next 18 to 24hrs. Conditions are forecast to improve on Tuesday in Nova Scotia.

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

None forecast.

 

Tonight/Tmrw Morning

Moderate to heavy rain shower activity with embedded thundershowers advances into the SW marine district.

 

Sunday

NS/NB/PEI : Heavy rainfall is forecast to develop and persist throughout the day. Local torrential downpours are the main concern, enhanced further by embedded thunderstorms. Areas at greater risk are marked in yellow.

 

Convective Discussion

High pressure is beginning its exit from the Maritimes today, giving way to a complex moisture feed developing off the US Eastern Seaboard. This weather maker will be the story for the Maritimes from Sunday into Tuesday. Pwats within are forecast to be over 60, which will lead to heavy rainfall and potential flooding concerns locally. Embedded thunderstorms will enhance totals further. A yellow area has been depicted for now showing upwards of 100 mm. Rainfall rates of near 30mm/hour are possible in this airmass. Unfortunately the airmass can’t advance very quickly through the area with the ridge remaining stubbornly positioned over Nfld for the period. Synoptic weather warnings will be used to alert the public of this developing weather situation.

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: A chance of thundershowers.

NS/NB/PEI/NFLD: None.

 

Tonight

NS/NB/PEI/NFLD/LAB: None.

 

Saturday

NS/NB/PEI/NFLD/LAB: None.

 

Convective Discussion

A departing upper low over northern Labrador with an associated surface trough will track across eastern labrador this afternoon. MLCAPE values are expected to be 250-500 J/kg and the effective shear will be 10 to 20 knots so any thundershowers will be weak in nature. On Saturday, an area of high pressure will move across the region so convection is not expected.  

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 scattered thunderstorms across eastern Labrador this afternoon with small hail, strong wind gusts, and locally heavy downpours.

NL: Chance of an elevated thundershower over the Avalon today with locally heavy downpours.

NS/NB/PEI: None.

Tonight

NS: Slight risk of an isolated thundershower overnight over northern Cape Breton.

NB/PEI/NL/LAB: None.

Tomorrow

LAB: Chance of scattered thundershowers across central and eastern Labrador tomorrow with gusty winds and locally heavy downpours.

NL: Slight risk of an isolated thundershower over central Newfoundland in the afternoon.

NS/NB/PEI: None.

 

Convective Discussion…

This morning, an upper low sits over northern Quebec with two troughs extending south. The first trough reaches from the Labrador Sea down into the Avalon Peninsula, then south into the Atlantic. Some lightning activity was observed in this trough overnight as it moved east across Newfoundland. The risk for an elevated thundershower continues early this afternoon for the Avalon, but the trough will slowly move east out of the region by this evening. A few brief heavy downpours will be possible in these thundershowers due to some high precipitable water over the area, with 41 mm observed on the 12Z St. John’s sounding this morning. Storms aren’t expected to become too organized here today however, due to a lack of instability in the weakening trough, but some marginally severe rainfall rates are possible due to the high precipitable water. Elsewhere, the second trough is slowly moving east and extends from the upper low through central Labrador, and down into the Gulf of Maine. Some thunderstorms are expected to trigger along this trough later this afternoon over eastern Labrador, where MLCAPE is forecast to rise near 750 J/kg in addition to a diverging 500 mb jet approaching from the southwest this morning. Some storms may become organized due to effective shear of 30 to 40 kts, but none are expected to reach severe criteria. PWATs over the area are forecast to be around 20 to 25 mm, so rainfall is not a primary concern. DCAPE close to 700 J/kg however could produce some strong wind gusts in the more organized cells.

Tonight, the second trough in question will continue to move east, extending down into the Gulf of St. Lawrence. A 250 mb jet will approach from the west, to lie over the surface trough overnight, which could spark up a brief thundershower or two. These cells could impact parts of PEI and northern Cape Breton overnight and into early tomorrow morning, but the risk remains low at this time. By tomorrow afternoon, both the jet and the trough will sit over central Newfoundland. MLCAPE is expected to remain near 500 J/kg here tomorrow, with the models showing some cloud cover lingering into the late morning. If this cloud is able to clear out a bit quicker than forecast, instability may be able to rise a bit higher but confidence is low at this time. Nonetheless, the risk does exist for an isolated thundershower or two over central Newfoundland tomorrow afternoon which could produce brief heavy downpours and some gusty winds. There is also the risk of some scattered thundershowers over central and eastern Labrador tomorrow afternoon around the upper low as it spins out over the Labrador Sea. Instability is expected to be lower here though, 250 to 500 J/kg MLCAPE, so the risk remains fairly low.

 

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/LAB: Slight risk for some isolated thunderstorms over northwestern New Brunswick and western Labrador late this evening with small hail, gusty winds, and locally heavy downpours.

NL: Chance of an elevated thundershower over western Newfoundland today with some locally heavy downpours.

NS/PEI: None.

Tonight

NL/LAB: Slight risk for an elevated thundershower overnight.

NB/NS/PEI: None.

Tomorrow

LAB: Chance for some scattered thunderstorms over southeastern Labrador with small hail, gusty winds, and locally heavy downpours.

NB/NS/PEI/NL: None.

 

Convective Discussion…

This morning, a disorganized elongated trough extends south from the Labrador Sea into the Atlantic waters south of Nova Scotia. Scattered thunderstorms in this trough have persisted overnight as it approaches western Newfoundland and southern Labrador, with this risk expected to continue through today. These storms are likely to stay elevated due to a thermal ridge between 750 and 800 mb evident on the 12Z Stephenville sounding, but an advancing shortwave near Cape Breton within the trough should keep scattered thundershowers going through the day. Weak MUCAPE values near 500 J/kg and effective shear of 10 to 20 kts will keep anything from becoming severe today over western Newfoundland, but some brief heavy downpours are possible with PWATs near 40 mm observed this morning at Stephenville. Elsewhere, a large trough over central Quebec will continue to move east this afternoon, reaching northwestern New Brunswick and western Labrador late this evening. A large capping inversion is present around 700 mb over New Brunswick, which is likely to keep any storms from firing this afternoon ahead of the trough. Good shear is in place (30 to 40 kts effective) and some clearing of the low level cloud is evident this morning which could help bump MLCAPE values upwards of 750 J/kg but this is unlikely to erode the cap. Due to the timing of the trough, thunderstorms aren’t expected to fire until late this evening, but by that point daytime heating will begin to shut down. The risk here today is low, but if anything is able to break the cap before the trough arrives it will have the potential to produce some gusty winds, small hail, and some heavy downpours.

Tonight, an elevated thundershower or two is possible over central Newfoundland as the first trough continues to move northeast and out over the Labrador Sea by tomorrow afternoon. The second trough impacting western Labrador and northwestern New Brunswick today will bring a similar risk for some scattered thunderstorms over southeastern Labrador tomorrow as it gradually moves east. A similar environment to today in the west is expected here, with the risk of some small hail, gusty winds, and locally heavy downpours.

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

NS/PEI/NB: Chance for some scattered thundershowers today across mainland Nova Scotia, eastern PEI, and southeastern New Brunswick with some gusty winds and locally heavy downpours.

LAB: Chance of an isolated thundershower along the Labrador coast this afternoon.

NL: None.

Tonight

NS/PEI/NL: Chance for some elevated thundershowers overnight.

NB/LAB: None.

Tomorrow

NB/LAB: Risk of scattered thunderstorms over northwestern New Brunswick and western Labrador late in the day tomorrow with small hail, gusty winds, and heavy downpours.

NL: Chance of an isolated thundershower over western Newfoundland through the day with locally heavy downpours.

NS/PEI: None.

 

Convective Discussion…

This morning, a weakening upper low sits over central Labrador, with an elongated trough extending south from the Labrador Sea into the Maritimes, where a weak surface low sits off the southwest coast of Nova Scotia. This surface low will be the main driver for convection today, with a few lightning strikes already observed offshore. Current model guidance already has some clearing over southeast New Brunswick and PEI, leading to forecast MLCAPE values of 750 to 1000 J/kg over this area, but persistent low level cloud cover over most of the Maritimes has held on this morning and the longer it sticks around, the less likely MLCAPE values are to build over 500 J/kg. Thus, most of the convection is likely to occur around the low center (where the best MUCAPE is available) as it slowly moves northeast through the day. Weak effective shear (~20 kts) is likely to keep storms from becoming organized, but due to the slow moving nature of the trough, as well as high PWATs (44.6 mm on 12Z Yarmouth sounding), some slow moving cells could drop some near-severe rainfall rates of up to 20 mm per hour over mainland Nova Scotia. Elsewhere, the upper low in Labrador could spin up some isolated thundershowers this afternoon. A bit more clearing is evident here which should allow some instability to build ahead of the upper low. Once again though, a lack of effective shear (15 to 25 kts) and some weak lapse rates will likely keep anything from becoming organized, but a few lightning strikes are possible.

Tonight, the surface low south of Nova Scotia will continue to move northeast to lie near PEI by late tomorrow morning. A slight chance of some elevated thundershowers are possible to the north and east of the low as some better jet support moves in from the West tonight. By tomorrow afternoon, the low will be approaching Newfoundland, which brings the risk for some elevated thundershowers to the western half of the island and southern Labrador. Weak lapse rates however keep the risk quite low but with similar PWAT to Nova Scotia today, some heavy downpours of 10 to 20 mm per hour are possible in any storms that do fire.

Late in the day tomorrow, a trough will approach from Quebec, bringing the risk for some scattered thunderstorms over northwestern New Brunswick and western Labrador. There is a lot of uncertainty with regards to initiation here, the first being the timing of the trough which is currently forecast to enter New Brunswick tomorrow evening. A large CAP is also evident between 700 and 500 mb which will likely keep storms from firing tomorrow afternoon ahead of the trough. Cloud cover could also pose an issue for convective initiation, with some hi-res guidance hinting at low level cloud lingering into the afternoon over most of New Brunswick. This would drastically limit MLCAPE from building during the day, severely limiting the environment storms can fire in. Given enough clearing tomorrow and if the trough moves through early enough, the risk does exist for some small hail, strong wind gusts, and locally heavy downpours across northern New Brunswick and western Labrador.

Thunderstorm Outlook for Today

Thunderstorm Outlook for Tonight

Thunderstorm Outlook for Tomorrow

Forecaster: Copp

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

Regional Impacts

 

Today

 

NB: Slight chance for isolated thundershower(s) spanning Northwestern NB. Hazards: 15-25 mm rainfall.

 

Tonight

 

NB/NS: Slight chance for isolated thunderstorm(s) spanning Southwestern NB and Western NS.

 

Tomorrow

 

NS/NB/PEI: Chance for isolated thunderstorm(s) spanning Southern NB, Mainland NS, and most of PEI. Hazards: 70 km/h wind gusts; 15-20 mm rainfall.

 

Wednesday

 

NS/PEI/NB: Likely for organized convection spanning NB, NS, and PEI. With largest risks over Eastern NB, Mainland NS, and PEI. Hazards: 70-90 km/h wind gusts; 2 cm hail; 15-25 mm rainfall.

 

NFLD/LAB: Chance for isolated thunderstorm(s) spanning Eastern Labrador and Northern Peninsula.. Hazards: 70 km/h wind gusts; 15-25 mm rainfall.

 

Convective Discussion

For today, satellite imagery and radar show a progressing warm trough through the Maritimes and Newfoundland & Labrador. As this trough progresses through the regions, there is a possibility of some clearing over northwestern NB. If this occurs, then some isolated thundershowers are possible, giving rainfall rates of 15-25mm/hr. However, looking at current upper air soundings and air quality, there is a large amount of convective inhibition (CIN) because of a large amount of stability, along with rising heights, that will need to be eroded before convection could occur. Further to this, air quality overnight was poor, which is indicative of smoke in the area. These are the biggest factors that convection will be fighting with today.

 

For tonight, there is not likely to be a significant change from today, except that there are likely to be lowering or neutral heights, which will allow some jets and vorticity to approach the western section of the Maritimes. This would allow for some elevated convection, and fairly weak from a convective aspect.

 

For tomorrow, we should see a continued breakdown of the heights and slight ridging that was found today and tonight over the Maritimes. This breakdown is likely to allow for CAPE values to approach 1,000 J/Kg with an Effective shear nearing 35 to 40KTs. This, paired with dCAPE (downdraft CAPE) values nearing 800 J/Kg, is allowing for isolated thunderstorms which could also produce wind gusts over 70km/h.

 

On Wednesday, an approaching frontal system is forecast to cross the Maritimes and primarily impact Eastern Labrador. This frontal system is possible to have a mix of CAPE values rising to near 2,000 J/Kg along with an effective shear layer approaching 50KTs, predominantly over NB/NS/PEI. These values could produce a range of hazards; with wind, rain, and hail as the primary threats, and current regional models do indicate a risk for a weak tornado. It is worth highlighting that this tornado risk is based on regional, non-convective-allowing models and could change as higher-resolution models come into scope.

 

Thunderstorm Outlook for Today

 

Thunderstorm Outlook for Tonight

 

Thunderstorm Outlook for Tomorrow

 

Thunderstorm Outlook for Wednesday

 

 

Forecaster: Lambert

 

Convective Outlook Valid for Today , Tonight and Tomorrow

Regional Impacts

NS… no thunderstorms expected.

PEI… no thunderstorms expected.

NB… tomorrow, some isolated thunderstorms possible with heavy downpours.

Newfoundland and Labrador… isolated pulse storms possible, showers with small hail or graupel possible.

Convective Discussion

For today, little convective activity is expected. A few lightning strikes are possible over central Newfoundland and western Labrador. Although upper-level support is fairly benign, a cold trough at 500 hPa may support weak updraft development. No hazardous weather is expected; however, any thunderstorms that do develop could produce locally heavier rainfall rates.

For tomorrow, stronger dynamics will move across western New Brunswick, with approximately 40 knots of deep-layer shear and total precipitable water values increasing to above 35 mm. However, surface-based convection may struggle to develop due to extensive cloud cover and a lack of strong low-level forcing. Earlier in the day, some embedded convection is possible, but the main potential for hazardous weather would occur later in the day if surface-based convection can develop.

Updraft strength is expected to remain a limiting factor, and mixed-layer CAPE values may not be sufficient to support deep convection. Additional guidance and observations tomorrow should provide a clearer picture of the overall severe weather potential.

 

Thunderstorm Outlook for Today

Thunderstorm Outlook for Tonight

Thunderstorm Outlook for Tomorrow

 

Forecaster: Mel Lemmon

Convective Outlook Valid for Today , Tonight and Tomorrow

Regional Impacts

 

Today

NFLD: A chance of thundershowers.

NS/NB/PEI/LAB: None.

 

Tonight

NS/NB/PEI/NFLD/LAB: None.

 

Sunday

NFLD: A chance of thundershowers.

NS/NB/PEI/LAB: None.

 

Convective Discussion

A departing low pressure system will give a chance of afternoon thundershowers across portions of Newfoundland this afternoon. MLCAPE values are expected to be 250-500 J/kg and the effective shear will be 10 to 20 knots so any thundershowers will be weak in nature. On Sunday, weak troughing over Newfoundland will give similar or weaker atmospheric conditions as today and a chance of afternoon thundershowers.  

Thunderstorm Outlook for Today

Thunderstorm Outlook for Tonight

Thunderstorm Outlook for Tomorrow