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