Convective Outlook Valid for Today, Tonight and Tomorrow

Regional Impacts

Today: Slight chance of an isolated thundershower along the Maine/New Brunswick border this afternoon.

Tonight: Risk of some isolated thundershowers over western New Brunswick before noon tomorrow.

Tomorrow: Chance for some scattered thundershowers across New Brunswick tomorrow. Locally heavy downpours are the main risk.

Convective Discussion…

Today, an upper low over southern Quebec will slowly move east as another intensifying low pressure system tracks off the Atlantic coast. Between these two systems, some convection has already fired over southern Maine under the left exit of the upper jet. This area will slowly move north and east through the day, likely triggering more convection through central Maine this afternoon. Due to the slow moving nature of the upper low, most of the thunderstorm activity today will remain west of the border, though a few cells may potentially cross into New Brunswick later this afternoon. Persistent low level cloud cover over southwestern New Brunswick should keep this risk fairly low, with MLCAPE values expected to remain well below 500 J/kg. Slightly better CAPE is expected in central Maine today, where cloud cover is more sparse allowing surface temperatures to rise. Although adequate bulk shear is in place, minimal instability and fairly weak lapse rates over New Brunswick should keep any storms from becoming severe.

Tonight, the upper low will continue to meander towards New Brunswick, crossing the province tomorrow. A similar environment to what is over Maine today will be in place over central New Brunswick tomorrow, bringing a slightly higher chance for some scattered thundershowers that may bring some locally heavy downpours.

Thunderstorm Outlook for Today

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Forecaster: Copp

Convective Outlook Valid for Today, Tonight and Tomorrow

Regional Impacts

Today: Risk of some isolated thundershowers in Newfoundland this afternoon. Locally heavy downpours are the main risk.

Tonight: No thunderstorms forecast.

Tomorrow: Slight chance of an isolated thundershower over western New Brunswick in the afternoon.

Convective Discussion…

As a ridge of high pressure dominates the Maritimes today, a weak shortwave will cross Newfoundland bringing the risk for some isolated thundershowers. Meager MLCAPE values (<500 J/kg) and weak bulk shear (15-20 knots) will keep any storms from becoming severe this afternoon, but a few locally heavy downpours are possible. An additional risk area exists in southwest Labrador, associated with a broad trough extending from western Labrador to southern Ontario, but there is a less conducive environment here.

Tomorrow, the above mentioned trough will slowly move east reaching western New Brunswick late in the day. This will bring the slight risk of some isolated thundershowers to extreme western New Brunswick late tomorrow. Most of the activity is expected to remain west of the Maine/New Brunswick border due to the timing of the trough.

Thunderstorm Outlook for Today

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Forecaster: Copp

Convective Outlook Valid for Today, Tonight and Tomorrow

Regional Impacts

Today: Isolated thundershowers possible in parts of NS, and central and northern parts of NB and across parts of Labrador. Embedded in nature, non-severe.

Tonight: No thundershowers forecast. Stable.

Tomorrow: Chance of a thundershower over eastern NS and parts of Nfld. Embedded, non-severe.

Convective Discussion

                With Fernand churning well offshore, a weak trof is located across the Maritimes, and another is cutting thru upstate NY. In clearing, and not in forest fire smoke, an area of instability exists with low to moderate skinny CAPE, and 10-20kts of effective shear this afternoon. There is substantial jet support out of the SW at 250mb of 140kts. The ingredients are in play much like yesterday to produce some -TS. Moisture remains low however, so large rainfall amounts are not forecast. This broad forcing progresses tomorrow to affect eastern NS and parts of Nfld as depicted. A sharper sfc trof is located across southern Labrador today and will also bring a chance of lightning and a few showers.

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Forecaster: Tirone.

Convective Outlook Valid for Today , Tonight and Tomorrow

Regional Impacts

Today: scattered to numerous thunderstorms across the Big Land this afternoon and into this evening giving locally heavy rainfall and possibly small hail. A slight risk of a thunderstorm early this afternoon for far northern NB. Also, a slight risk of an embedded thundershower early this afternoon for the eastern Avalon.

Tonight: risk of thunderstorms for central areas of Labrador.

Convective Discussion

Decent dynamics at play today for a good portion of Labrador as a strong short wave trough ahead of the main long wave trough gives way to thunderstorms this afternoon and evening mainly across the interior, but they will likely traverse east northeastward and into coastal areas later today then over the Labrador Sea tonight given the good upper support. Locally heavy rainfall seems to be the main threat but gusty winds as well, given the effective shear is in the 30 to 35 knot range. The 12Z tephi out of YZV shows some steep lapse rates in the mid levels so, given some sunshine, could produce modest CAPE and enough updraft to support small hail in the stronger cells. I do not expect severe criteria to met. There will be a slight risk of an early afternoon thunderstorm for far northern NB as that short wave passes north of the region and into Labrador, but time is running out on that happening. Lastly a slight risk of an early afternoon embedded thundershower for the eastern Avalon as a thermal ridge moves east of the island.

There is a risk of thunderstorms for central Labrador through the night as that short wave trough remains in the area.

Thunderstorm Outlook for Today

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Jeremy

Convective Outlook Valid for Today , Tonight and Tomorrow

Regional Impacts

Today: risk of an embedded thundershower for eastern NS giving torrential downpours. Isolated thunderstorms possible for northwestern NB and parts of Labrador giving heavy downpours and gusty winds.

Tonight: continuing with the risk of an embedded thundershower for eastern NS and a portion of NL giving torrential downpours.

Tuesday: once again a risk of an embedded thundershower across southeastern NL giving heavy downpours. Scattered thunderstorms likely for most of Labrador and northern areas of NB giving heavy downpours, gusty winds and small hail.

Convective Discussion

A couple areas to watch today through to Tuesday. The first is an approaching frontal trough and associated thickness ridge moving up south of Nova Scotia that will move eastward into NL tonight and Tuesday. The PWATs with this feature could be in excess of 50 mm so torrential rainfall is a definite concern. But there looks to be a very limited chance in seeing lightning due to the warming aloft creating a stable, nimbostratus-type profile. The instability seems to get good just in behind the thermal trough, basically when the precipitation is ending from west to east. But no doubt some embedded deep layer TCUs capable of dropping copious amounts of rain over a short period of time.

The second feature is an upper-level trough that will give bouts of non-severe thunderstorms to north/northwestern NB today and Tuesday as well as a good chunk of Labrador, as short wave troughs move up along the base of the long wave trough.  As freezing levels lower on Tuesday, some small hail is possible in some of the stronger cells.

Thunderstorm Outlook for Today

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Jeremy

Convective Outlook Valid for Today, Tonight and Tomorrow

Regional Impacts

Today:

LAB: Risk of isolated thunderstorms over west LAB: Risk of isolated thunderstorms over southern Labrador.ern Labrador giving locally heavy downpours, strong wind gust and small hail.

NB: Risk of an isolated thunderstorm over extreme northwestern NB.

NS/PEI/NL: No thunderstorms forecast.

Tonight:

LAB: Risk of isolated thunderstorms over southwestern Labrador.

NB: Risk of an isolated thunderstorm over extreme northwestern NB.

NS/PEI/NL: No thunderstorms forecast.

Tomorrow:

NB: Risk of isolated thunderstorms giving locally heavy downpours and strong wind gusts.

NS: Risk of embedded thunderstorms giving locally heavy downpours.

LAB: Risk of isolated thunderstorms over southern Labrador.

NL:PEI: No thunderstorms forecast.

Convective Discussion

As a low pressure system over James Bay remains stationary, a warm front is moving across southern Labrador this morning with a cold front extending from western Labrador southwest towards the St. Lawrence River. The cold front this afternoon will trigger some thunderstorms across central Quebec and towards western Labrador by late afternoon or early evening. With CAPE values reaching 500 J/kg and increasing effective shear of 30kt, some thunderstorms may organize into multicells or lines prior to reaching. With freezing levels at around 10,000 ft and sufficient lift, small hail is also possible. Convection is expected to remain mainly west of New Brunswick today but may graze parts of western Madawaska and Restigouche counties.

Tomorrow, the front stalls over western New Brunswick while a low pressure system is expected to form off Cape Hatteras later today and move northeast towards Nova Scotia tomorrow. High rainfall amounts and embedded thunderstorms are possible mainly over coastal Nova Scotia and southern marine waters leading to potential locally heavy rainfall as precipitable water increases to more than 50 mm. The cold front will continue to spark thunderstorms for the afternoon in northwestern New Brunswick. CAPE values may only reach 250 but there is moderate bulk shear and increasing precipitable water so strong winds and heavy downpours are possible. A trough line may also spark a few embedded thunderstorms across southern Labrador as that tracks slowly northward.

Thunderstorm Outlook for Today

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Roberta McArthur

 

 

Convective Outlook Valid for Today, Tonight and Tomorrow

Regional Impacts

Today: No thunderstorms forecast in Atlantic Canada.

Tonight: No thunderstorms.

Tomorrow: Non-severe thundershowers possible over extreme western Labrador.

Friday: Organized thunderstorms are forecast in the right quadrant of Erin over the southern-most marine regions.

Convective Discussion

Nil sig weather convection wise across the Atlantic domain until tomorrow late day. An advancing trof in central and northern Quebec may bring a lightning strike or 2 embedded in some shower activity late day tomorrow in parts of western Labrador. The bigger weather system to watch in next 3 days in Erin. Detailed hurricane forecast information can be found on weather.gc.ca/hurricane. Thunderstorms associated with this system will creep into the marine domain on Friday (into Saturday). They may push orange limits for rain and wind gusts near the southern border of our Canadian domain.

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Thunderstorm Outlook for FRIDAY

 

 

Forecaster: TIRONE.

Convective Outlook Valid for Today, Tonight and Tomorrow

Regional Impacts

Today:

NL: Risk of isolated embedded thundershowers over the eastern Avalon Peninsula and east coast.

NB/NS/PEI/LAB: No thunderstorms forecast.

Tonight:

No thunderstorms forecast.

Tomorrow:

No thunderstorms forecast.

Convective Discussion

Isolated embedded thundershowers affected parts of the Avalon and the northeast and east coasts of Newfoundland overnight and this morning as an upper low continues to slowly move east into the northern Grand Banks today. Showers and drizzle are expected to continue for most of Newfoundland in a strong northerly flow today with an odd thunderstorm still possible today mainly east of the Avalon. Otherwise, a ridge of high pressure will remain over the Maritimes this week limiting potential for convection. A weak trough over central Quebec will bring some isolated showers to parts of northern Labrador tomorrow, but are not expected to produce any thunderstorms at this time.

Thunderstorm Outlook for Today

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Roberta McArthur

 

Convective Outlook Valid for Today , Tonight and Tomorrow

Regional Impacts

Today: risk of an embedded thundershower over southeastern NL.

Tonight: risk of an embedded thundershower over eastern NL.

Tuesday: risk of an embedded thundershower over the Avalon Peninsula.

Convective Discussion

A developing upper low will be the only weather to talk about this week. There has been very little in the way of lightning up until now, but the instability does get better later today, through tonight and into early Tuesday. So, there should be some isolated elevated thundershowers as the upper low spins around eastern/southeastern NL. The PWATs are relatively low however, areas of convection will be very slow to move so locally heavy rainfall amounts are a concern with this feature.

Thunderstorm Outlook for Today

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Jeremy

Convective Outlook Valid for Today , Tonight and Tomorrow

Regional Impacts

Today: slight risk of an afternoon or evening thunderstorm across south/southwestern NB.

Tonight: slight risk of an embedded thundershower along the South Shore of NS.

Convective Discussion

A weakening cold front currently lying across northern NB will slide southeastward today and tonight giving just a slight risk of a thunderstorm across southern areas of the province. The better instability along with the low-level moisture will remain in southern New England but an isolated cell or 2 could advect into the southwest this afternoon giving locally gusty winds. Aside from that there will also be a slight risk of an elevated, embedded thundershower over southwestern NS tonight as the front passes through. There have been some isolated wind gusts close to 40 knots just in the wake of the front in northern ME so cannot rule out the same for some areas of northern NB today.

Thunderstorm Outlook for Today

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Jeremy

Convective Outlook Valid for Today , Tonight and Tomorrow

Regional Impacts

Today and tonight: nil.

Sunday: risk of an afternoon or evening thunderstorm across southern areas of NB.

Convective Discussion

A cold frontal trough will cross NB during the day Sunday but will be weakening quite a bit. So just the slightest risk of a thunderstorm across the south in the afternoon and evening.

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Jeremy

Convective Outlook Valid for Today , Tonight and Tomorrow

Regional Impacts

Newfoundland and Labrador…. Scattered thunderstorms giving locally heavy downpours for central and eastern Newfoundland.

PEI… No impacts.

NS… No impacts.

NB… No impacts.

Convective Discussion

Thunderstorms will continue to develop ahead of the cold front moving across Newfoundland today. The same airmass that brought localized rainfall amounts exceeding 50 mm to parts of the Maritimes has now shifted over Newfoundland. The timing of the front will likely limit deeper convection due to reduced daytime heating.

With precipitable water (PW) values near 35 mm and most unstable CAPE between 500 and 1000 J/kg, there remains some potential for locally heavy downpours. Given the front’s forward speed, back-building thunderstorms are not expected; however, there is a slight risk of this occurring across central and northeastern Newfoundland.

Following the passage of the front, most of the region will see much drier conditions over the next couple of days, with little in the way of active weather until Sunday or Monday, when another system is expected to bring some precipitation. This next front is unlikely to produce as much active convection as the current one.

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Mel Lemmon

Convective Outlook Valid for Today , Tonight and Tomorrow

Regional Impacts…

 

Today

NB/NS/PEI: Scattered severe thundershowers.

Labrador/Newfoundland: Scattered non-severe thundershowers.

 

Tonight

NS/PEI/Newfoundland: Scattered non-severe thundershowers.

NB/Labrador: None.

 

Friday

Newfoundland: Scattered non-severe thundershowers.

NB/NS/PEI/Labrador: None.

 

Convective Discussion

A cold front stretching from Labrador to central New Brunswick will slowly continue eastward today. Over southern New Brunswick, Prince Edward Island and portions of Nova Scotia severe weather is possible near and ahead of the front this afternoon and evening.  CAPE values of 1000-1500 J/kg are expected and effective shear will be 20-30 knots. Additionally, a supportive right entrance region of the upper jet will move over southern New Brunswick this afternoon and support convection. The airmass ahead of the cold front remains very moist with PWAT values of 40-50 mm. Due to some cloud cover, the thunderstorms will be a combination of embedded and surface based. Over western Newfoundland and eastern Labrador, non-severe thundershowers are likely today. CAPE values of 500-750 J/kg are expected with effective shear of 20-30 knots. There is a fair amount of cloud cover so that should mitigate severe weather there. On Friday,  non-severe thundershowers are expected over eastern Newfoundland associated with the same cold front.

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Convective Outlook Valid for Today , Tonight and Tomorrow

 Regional Impacts…

 

Today

Labrador: Scattered severe thundershowers.

NB/NS: Scattered non-severe thundershowers.

PEI/Newfoundland: None.

 

Tonight

NB/NS/PEI/Labrador: Scattered non-severe thundershowers.

Newfoundland: None.

 

Thursday

NB/NS/PEI/Newfoundland/Labrador: Scattered non-severe thundershowers.

 

Convective Discussion

A slow moving cold front will drift across Labrador today and Thursday. The same front will move across New Brunswick on Thursday. Over Labrador, severe weather is possible ahead of the front this afternoon and evening.  CAPE values near 1500 J/kg are expected and effective shear will be 30-40 knots. Additionally, a supportive right entrance region of the upper jet will move over western Labrador this afternoon. Over New Brunswick and western Nova Scotia today non-severe thundershowers are possible. CAPE values near 2000 J/kg are expected but effective shear will only be 10-20 knots and only weak forcing mechanisms are anticipated. On Thursday, the convection should become more embedded in nature but  some surface based convection is still possible. CAPE values of 500-1000 J/kg are expected. Effective shear near 20 knots is anticipated over the Maritimes and closer to 30 knots over Labrador. Cells could become near severe with rain and wind but should stay below warning conditions.

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Convective Outlook Valid for Today , Tonight and Tomorrow

Regional Impacts

Newfoundland and Labrador… some thunderstorms can be expected in southern Labrador with strong winds and possibly heavy downpours.

PEI…none expected.

NS… a low chance of an isolated thunderstorms inland.

NB… a risk of thunderstorms tomorrow, some isolated downpours possible.

Convective Discussion

Yesterday was fairly active across Labrador, although most thunderstorms occurred well north of the forecast regions. Today, the southern part of Labrador is more likely to see similar activity. The zonal upper jet will remain quasi-stationary through central Labrador and is generally aligned with the flow down to the surface. While updrafts are not expected to be particularly strong, low-level winds exceeding 30 knots could mix down to the surface in some thunderstorms.

Over the Maritimes, dynamics are less favourable; however, potential energy is relatively strong, with mixed-layer CAPE values near 1000 J/kg. A lack of forcing will limit the ability for convective clouds to reach their level of free convection, with the exception of a very slight chance over southwest Nova Scotia.

Tomorrow, weak surface troughing may provide slightly more favourable conditions for scattered thunderstorms across New Brunswick. These are expected to be very isolated and are unlikely to produce widespread rainfall.

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Mel Lemmon

Convective Outlook Valid for Today , Tonight and Tomorrow

Regional Impacts

Newfoundland and Labrador… Some isolated thunderstorms over Labrador today and tomorrow, strong wind gusts and heavy downpours possible.

NB… No impacts expected.

NS… No impacts expected.

PEI… No impacts expected.

Convective Discussion

Labrador will experience the bulk of convective activity over the next two days, with the potential for severe thunderstorms, including discrete supercells. Atmospheric dynamics are generally favourable, with deep-layer wind shear between 40–50 knots and 0–3 km shear values of 30–40 knots. Moderate CAPE values will also contribute to storm development, with some areas exceeding 1000 J/kg.

For the most part, the shear is predominantly linear, and triggering mechanisms will be somewhat limited. Troughing and surface convergence are expected to be subtle, and differential heating may play an ongoing role. Clear skies will enhance solar insolation, further aiding destabilization.

If severe storms develop, it is unlikely that any single community will be directly affected unless an organized mesoscale convective system (MCS) forms, producing a more continuous gust front. We will monitor satellite and lightning detection closely as the day progresses.

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Mel Lemmon

Convective Outlook Valid for Today , Tonight and Tomorrow

Regional Impacts…

 

Today

NB/NL/Labrador: Scattered non-severe thundershowers.

NS/PEI: None

 

Tonight

NB/NS/PEI/NL/Labrador: None

 

Monday

Labrador: Scattered non-severe thundershowers.

NB/NS/PEI/NL: None

 

Convective Discussion

 

A weak trough over northern New Brunswick may trigger scattered thundershowers this afternoon. CAPE values near 1000 J/kg are expected but the effective shear is low at less than 20 knots. Gusty winds and downpours in the moistening airmass are possible in the non-severe cells. Weak troughing over Newfoundland and Labrador may produce scattered thundershowers this afternoon. CAPE values of 500 J/kg or less should limit any weather to non-severe. On Monday, a cold front sweeping across Labrador will give scattered thundershowers. Again, CAPE values of 500 J/kg or less should limit any weather to non-severe.

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