Convective Discussion
Isolated non-severe elevated CBs are expected near a surface low located southeast of Cape Breton which is moving slowly northeastward. These CBs will give embedded heavy downpours. Another area of non-severe elevated CBs is expected in the warm sector of the frontal wave over the southern Grand Banks, mainly near or just east of the cold front.
Regional Impacts
Nova Scotia: non-severe embedded thunderstorm for eastern parts of the province. Local heavy showers and some wind gusts.
Newfoundland/Labrador/Prince Edward Island/ New Brunswick: none.
Grand Banks: embedded convection east of the cold front of the low, weakening to the north over colder water.
Spencer Clements
Convective Discussion.
No activity expected in the region today.
Regional Impacts.
Nil.
Jeremy
Convective Discussion.
Only some scattered cells across the southern Grand Banks and slope waters south of NS today in association with a trough of low pressure. Quiet weather elsewhere.
Regional Impacts.
NS/NB/PEI/Newfoundland/Labrador: nil
Convective Discussion.
There are a couple features worth noting today. First off there is some elevated convection associated with the thickness ridge near the Avalon this morning. This is lying along the 850 thermal ridge and very high PW. Heavy downpours to affect the SE Avalon over the next hour or so. The second feature is a cold front over western NL. Upper level analysis shows a very strong 250 jet (but not in a favorable position). There is plenty of shear (50+ knots), but the instabilities are not that strong. And sat pix shows a lot of cloud cover. If this does burn off allowing some partial clearing there could be a couple decent cells develop this afternoon (across WRN/CNTRL NL) that could give some strong wind gusts. Small hail is also a possibility.
Regional impacts.
Newfoundland: locally heavy downpours across the SE Avalon. SCT cells this afternoon for CNTRL/WRN areas giving some gusty winds.
Nova Scotia, New Brunswick, PEI and Labrador: nil.
Jeremy
Convective Discussion.
A frontal wave currently over the lower St Lawrence will continue to move eastward today under a very strong upper level wind flow. The surface cold front has moved south of the St Lawrence river this morning and dry/stable air is now found west of it. The low cloud continue to dissipate over the Maritimes as the cold front approaches. Ahead of the front, the air mass remains marginally unstable and with the some limited daytime heating of the surface scattered thunderstorms will develop once a warm layer in the low to mid levels becomes eroded. Current radar indicates early development over the mountains of the Eastern Townships and Maine Highlands. These storms will propagate eastward as the front pushes through NB later in the day.
Regional Impacts.
Newfoundland&Labrador: Isolated non-severe thunderstorms.
Nova Scotia: Risk of a thunderstorm over central, northern and eastern regions.
New Brunswick: Scattered thunderstorms developing west of the region moving east. The main threat is very high wind gusts.
Prince Edward Island: Risk of thunderstorms late today.
Jean-Marc
Convective Discussion.
A frontal wave over southern Quebec will reach the Maritimes tonight. Ahead of this feature, an area of showers currently over the lower St Lawrence will reach northwestern NB this afternoon. This morning’s soundings from the area are showing limited potential energy so any daytime thunderstorms activity will be limited to Maine and Quebec.
This evening and overnight the air mass will become much more humid and unstable as a trough pushes through. Some residual convective features from the west will also spread across the Maritimes, especially across western NS where downpours are likely.
Regional Impacts.
Newfoundland: none.
Labrador: Scattered showers only.
Nova Scotia: Dry today, Numerous thundershowers tonight with downpours likely over western sections.
New Brunswick: Scattered showers in the northwest today, risk of thundershowers across the province tonight.
Prince Edward Island: Dry today, risk of thundershowers tonight.
Jean-Marc
Convective Discussion.
A few areas of convective activity to note mainly over Newfoundland and Labrador today as a quasi-stationary low over northern Quebec with a trough extending through Labrador, Newfoundland, and eastern Nova Scotia today.
The air mass within the trough extending from Newfoundland towards eastern Nova Scotia is quite moist in the low levels with dew points remaining near 20C. Surface temperatures are already near the daytime highs expected over western areas of Newfoundland despite the current cloud cover. The question will be how much additional surface based heating there will be should the cloud break up more. The inhibitor for this afternoon is a slight warming expected in the mid levels which could cut the potential energy of any convection that develops. Despite this, any showers already on the go and what could develop this afternoon will produce locally heavy downpours given the high pecipitable water values in the area as well as strong wind gusts. There should only be a slight risk of a thundershower over eastern Nova Scotia early this afternoon as the trough is currently moving over the area and some coastal convergence could provide further lift. Dew points will still remain high for a few hours after this trough moves through as the more pronounced change in humidity is still further west over New Brunswick.
For central Labrador, the area remains under an unstable westerly flow. A 500mb cold pool lies over central Quebec to central Labrador providing sufficient lift given daytime temperatures in the upper teens. Air mass type thunderstorms are expected but some further organization is possible given convergence near the trough and low pressure centre that is expected to form over eastern Labrador this evening and push off into the Labrador Sea tomorrow morning. Precipitable water remains moderately high so convection this afternoon will likely produce some heavy downpours. Hail is also a risk with freezing levels dropping below 10,000ft.
Regional Impacts.
Newfoundland: Locally heavy downpours and strong wind gusts.
Labrador: Locally heavy downpours, strong wind gusts, and small hail.
Nova Scotia: An isolated thundershower over eastern sections this afternoon.
New Brunswick and Prince Edward Island: nil
Roberta McArthur
Convective Discussion.
It should be active afternoon and evening for much of western New Brunswick and into the rest of the Maritimes and Labrador overnight as a short wave trough extending from a low pressure system over Hudson Bay tracks through the region.
A warm front has been producing some heavy showers and occasional embedded thundershowers this morning over Maine which will continue into New Brunswick and the Bay of Fundy but will also continue to fizzle into the afternoon. The cold front is not far behind over southern Quebec and will begin to track through New Brunswick late this afternoon and into tomorrow morning over Nova Scotia and Newfoundland.
For New Brunswick behind the warm front this morning, there should be some clearing in the warm sector ahead of the approaching cold front this afternoon. Low-level moisture is already quite high in the region with dew points 18-20C and precipitable water values reaching 40 mm. Surface based convection is expected to begin this afternoon as temperatures reach the mid 20s given sufficient clearing. Upper divergence and further cooling aloft will provide further instability into the afternoon with CAPE values nearing 1000 J/kg over northwestern New Brunswick. Low to mid-level shear is also expected to increase to 30-40KT by the evening. These ingredients will all help to initiate and potentially sustain severe thunderstorms into the evening. Multicells may organize into bow lines or supercells ahead of the cold front. The main threat will be heavy downpours, strong wind gusts, and small hail. The potential for a tornado cannot be ruled out given the amount of low-level shear mainly over northwestern New Brunswick as well.
Over Labrador, there risk of non-severe thunderstorms over central and western areas as late this afternoon and evening as the trough from the low pressure centre over Hudson Bay progresses northeastward. Locally heavy downpours are possible.
Regional Impacts.
New Brunswick: Strong wind gusts which may approach 90 km/h, locally heavy downpours(25+mm), and small hail (1-2cm.
Nova Scotia and Prince Edward Island: Locally heavy downpours and strong wind gusts.
Labrador: Locally heavy downpours
Newfoundland: Nil
Roberta McArthur
Convective Discussion
A weakening short wave trough with an area of light to moderate rain over Maine this morning is expected to break up into scattered showers this afternoon as it pushes into western New Brunswick. The risk for thundershower activity this afternoon should remain over Maine into southern Quebec where dynamics are more favourable.
Meanwhile, there is a low pressure system over Ungava Bay slowly tracking eastward with a cold front extending south and westward toward northern Labrador and Quebec. Ahead of this cold front, there may be enough upslope lift over the Torngat Mountains combined with an approaching 30KT 850mb jet to initiate some elevated convection this afternoon. Central Labrador remains in an unstable southwesterly flow and temperatures may be close to reaching their convective temperature needed to initiate thunderstorms this afternoon but there is a lack of a real trigger and with moisture dropping this afternoon and a warm layer at 700mb, there is less of a risk other than scattered TCUs in showers.
Regional Impacts
Labrador
Possibility of isolated thundershowers over the Torngat Mountains ahead of the cold front this afternoon. TCU in showers for central Labrador.
New Brunswick
Showers with possible local heavy downpours this afternoon over western sections.
Newfoundland, Nova Scotia and Prince Edward Island
None expected
Roberta McArthur
Convective Discussion
Atlantic Canada is mainly under the influence of a ridge of high pressure today which will suppress convection over the Maritimes. Sea breeze convergence will provide some lift and isolated showers are possible for Newfoundland this afternoon and evening. There is a weak upper level trough over North Shore Quebec moving eastward towards southern Labrador today which will provide further instability with some cooling aloft. In addition, some coastal convergence and upslope flow will help to produce some isolated thundershowers this afternoon over central and southeastern Labrador. Given only weak shear, locally heavy downpours will be the main threat. With CAPE values of around 250 J/kg and freezing levels near 8,000ft in the area, there is also a slight risk of small hail.
Regional Impacts
Labrador
South central and eastern Labrador – Risk of thunderstorms with heavy downpours and a slight risk for small hail.
Maritimes and Newfoundland
None expected
Roberta McArthur
Convective Discussion
A quiet day across Atlantic Canada as a low pulls away northeast of Newfoundland and high pressure moves in. No convective activity expected.
Regional Impacts
Atlantic Canada
None
Barrie MacKinnon
Convective Discussion
The focus will be over Newfoundland today where thunderstorms are expected. A very healthy strengthening jet over the area brings 0-6 km wind shear values near 40 kts which is expected to increase to near 60 kts later this afternoon for some areas. At the current forecasted temperatures highs, 500 J/kg can be expected with higher amounts possible if highs reach a few degrees above forecasted temps. A trough over the Maritimes will help kick start convective activity and low freezing levels of around 8500 ft could make hail a possibility under some of these storms. Areas that stay cloud covered throughout the day should see reduced convective activity. It is possible that some of the cells that develop may become severe. Heavy rainfall and hail are the main threat if severe thunderstorms develop. The increasing wind shear later today could actually help to limit convection as t-storms development could be sheared off.
Regional Impacts
New Brunswick
Non expected
Nova Scotia and PEI
None expected
Newfoundland
Thunderstorms of which a few severe thunderstorms are possible. Heavy rainfall and large hail are possible.
Labrador
Southernmost coastal Labrador – Risk of thunderstorms with slight chance of severe tstorms. Heavy rainfall and large hail possible.
Barrie MacKinnon
Convective Discussion
Most of the Atlantic provinces are under a dryer airmass after the passage of the cold front over the weekend, maximum dewpoints are generally around 16C which is on the low side for deep convection but still sufficient. With the lower moisture levels the overall amount of Convective available potential energy(CAPE) is generally low with the exception of southern New Brunswick where cape values could exceed 1000 j/kg. In terms of the dynamics the approaching upper level jet may provide some needed support to maintain convection later in the day, this along with falling heights and 40 to 50 knots of deep shear mean that severe thunderstorms are possible later this afternoon for New Brunswick. However, it may be a challenge to initiate thunderstorms with the lack of a strong trigger but a weak trough this afternoon may provide adequate lift to get things started. Watches may me issued for New Brunswick if thunderstorm activity begins.
For the remainder of the Maritimes there remains a low probability of severe thunderstorms however with improving dynamics thunderstorms could linger well into the evening.
For southern Labrador the dynamics, windshear and moisture shouldn’t be an issue but steepening lapse rates through the day may lead to airmass thunderstorms developing and continuing into the evening.
Regional Impacts
New Brunswick
Severe Thunderstorms Possible. Small hail, locally heavy downpours and potentially damaging winds. Mainly over southern New Brunswick.
Nova Scotia and PEI
Low probability of Severe Thunderstorms. Locally heavy downpours and strong wind gusts possible.
Newfoundland and Labrador
Airmass thunderstorms possible for southern Labrador. Locally 20mm rain, small hail, some gusty winds.
Mel Lemmon
Convective Discussion
There will be much less convection in Atlantic Canada today than yesterday overall. The surface cold front and area of PVA associated with the upper trough has moved past the western Maritimes and is over the Gulf of St. Lawrence. Therefore, convective activity today should be confined to the Gulf of St. Lawrence region, western Newfoundland and parts of central and eastern Labrador. There is diffluence in upper flow east of the Maritimes. There is also a cold trough in the 500 mb flow over the Maritimes and eastern US.
The 12 Z sounding from Stephenville shows significant instability above 850 mb. However, this sounding also shows a cap between 600 and 500 mb. My thinking is that falling heights associated with the approaching upper trough and the PVA should allow convection to initiate this afternoon over western Newfoundland. There should be enough sunshine to assist in initiation of convection in this area. There is significant shear in this area, 40 to 50 knots in the 0-6 km layer. CAPEs would be in the 500-1000 J/kg range. There is a possibility that storms similar to what occurred in the Maritimes yesterday could occur in the yellow region, with gusty winds, hail and heavy downpours.
Elsewhere in NL, There is a cap at about 650 mb limiting convection in eastern Newfoundland. Over Labrador, thundershowers have been occurring and will continue to occur today. This is associated with the upper low. These thundershowers should not be severe because the is very low shear. However heavy downpours and small hail are a possibility.
Regional Impacts
Maritimes…
Isolated thundershowers possible over eastern NS and PEI.
Newfoundland and Labrador…
Thundershowers likely for western Newfoundland. Risk of thundershowers for central/eastern Labrador.
Steve
Convective Discussion
There are residual low clouds associated with a departing low pressure system east of Newfoundland. Elsewhere across the Atlantic provinces, the upper ridge continue to prevail today preventing any convective cloud to form.
Two upstream systems may impact the parts of the region in the medium term:
A frontal wave over northwestern Quebec will advance towards western Labrador tonight and Wednesday bringing a slight risk of thundershower;
Another frontal wave, over the Gulf stream will push a humid air mass over Nova Scotia offshore waters bringing scattered thundershowers along with a chance of downpours and locally gusty winds.
Regional Impacts
Newfoundland: Nil
Labrador: Slight risk of thundershowers early Wednesday
NB and PEI: Nil
NS: Downpours and higher gusts near thundershowers for offshore waters
Jean-Marc
Convective Discussion
At the surface, a cold front stretches north-south over eastern portions of Newfoundland. An upper cold low will remain parked over the lower Quebec North Shore today, eventually moving east of Labrador Tuesday.
A cluster of lightning associated with the cold pool persists this hour over southeastern Labrador, and this activity is expected to continue well into the afternoon. An upper trough extending southward from the upper low along the west coast of the island will move across central regions this afternoon triggering isolated thundershowers ahead of it. The main threat with these storms is brief heavy downpours and gusts up to 70 km/h.
Tranquil weather conditions are expected across the rest of the Atlantic provinces this afternoon.
Regional Impacts
Newfoundland: potential for brief heavy downpours (20 mm) for northern, central and eastern regions of the island
Labrador: potential for brief heavy downpours (20 mm) over southeastern regions
NB, NS and PEI: Nil
Jean-Marc
Convective Outlook.
There are a couple areas of concern today: one over central NL and the other along portions of NS. First in NL, elevated morning convection giving locally heavy downpours should weaken in the coming hours. If things clear in the SW after lunch there is plenty of CAPE (1000 j/kg or more) so cells could fire fairly quickly and move northeastward through the afternoon and into the evening. Based on the 12Z YJT tephi the shear is low, but freezing levels are fairly low as well. Could be some strong wind gusts and small hail, but the main threat would be torrential downpours with 25 mm/h possible.
Now for NS. After analyzing things from the surface to 250 all the ingredients are there for a potentially stormy afternoon (of course, from experience working the desk this not always pans out). There is a 90 knot 250 mb jet observed in YQI placing NS in the left exit region. There is a strong 50 knot jet along SW NS with an approaching upper trough to the west, with 40-50 knots of shear along with falling atmospheric heights. There is also an approaching 700 mb trough. Sat pix shows plenty of sunshine to aid convection at the moment (need to keep an eye on some mid-level cloud sneaking into SW regions). There is a thermal ridge at 850 pushing into the province and an approaching surface cold front, that at 12Z, was analyzed to be somewhere near western and northern portions of the province. Dewpoint temps should be in the upper teens this afternoon proving the moisture. There were a couple severe cells in NB yesterday with Tds several degrees cooler, so confidence is fairly high that we see a couple strong storms this afternoon and into this evening. In addition, CAPE values could be up around 1500 j/kg. The instability won’t be that strong as LI’s will be around -4, but with all the other ingredients, this shouldn’t be of concern as a limiting factor at all. Torrential downpours and strong winds are the main threats…though some small hail is also possible.
Regional Impacts.
Newfoundland: potential for very heavy downpours with cells today across central regions of the island…25 mm/hr.
Nova Scotia: potential for very heavy downpours and strong winds from Queens County through to Pictou and Antigonish (including all counties along the ATL coast of NS) as well as Cape Breton.
PEI: slight risk of a thundershower for eastern portions of the Island.
NB/LAB: nil.
Jeremy
Convective Discussion.
There are a couple areas today that run the risk for some thunderstorms. First is across WRN/CNTRL LAB where an upper trough will produce some TCU and SCTD CBs this afternoon. There is very little shear and lack of moisture, but freezing levels are fairly low. Some small hail is a possibility. SAT PIX is showing the cloud breaking up which will aid their development.
The second area will be across NRN/CNTRL NB this afternoon and into this evening. KCAR is showing decent shear (40-45 knots), but is lacking low level moisture. Also modifying for a convective temperature of 27 only gives a few hundred J/KG of CAPE. An upstream upper level trough will help to initiate some convection after lunch. Given the dry air below 700 mb, there could be some modest dry microbursts in the stronger cells. Right now severe storms are not expected…and just a slight chance in seeing near severe storms this afternoon and into this evening. Local downpours are also possible along with small hail. Later tonight, some of the convection may slide south and eastward affecting SRN NB and parts of PEI.
Regional Impacts.
Labrador: scattered non-severe cells this afternoon for central and western regions.
New Brunswick: scattered storms this afternoon and evening for central and northern portions of the province. Gusty winds and small hail with some cells.
PEI: risk of seeing a TRSA tonight as convection drifts eastward from NB.
Nova Scotia/Newfoundland: nil.
Jeremy
Convective Discussion
A couple of upper level disturbances are affecting Labrador today, while a trough continues to pull east of Newfoundland. Convection has been ongoing over eastern marine waters from the southern Grand Bank northeastward towards Funk Island Bank this morning and is expected to pull east of the marine waters this evening. With the aid of some coastal convergence and slight cooling aloft, southeastern Labrador could see some thundershowers this afternoon. Freezing levels are fairly low but there is still a decent amount of precipitable water so heavy downpours and small hail is possible.
A weak low pressure area currently south of James Bay will continue tracking to the southeast. A trough extending southeast of the low will bring some isolated showers to northern New Brunswick this evening and overnight. At this time the dynamics do not look favourable to initiate any surface based thundershowers as there is a considerable cap at 950mb based off the Caribou sounding to overcome.
Regional Impacts
Labrador…Lightning, locally heavy downpours and small hail are possible for southeastern Labrador.
Maritimes and Newfoundland…None
Roberta McArthur
Convective Discussion
Another active day for the Atlantic provinces today. A trough stretching from central Labrador to southwestern Nova Scotia will slowly progress eastward this afternoon. Along and ahead of the trough, moisture remains high with dew points in the 18-20 degree range. Along with some solar insolation and a slight increase in 0-6km shear, thunderstorm development will likely initiate this afternoon and continue into the evening. There has already been some elevated convection this morning over Newfoundland that will continue to push to the northeast. There is a thicker cloud band with isolated showers stretching the Gulf of St. Lawrence toward southwest Nova Scotia. Should this cloud break up this afternoon, surface based CAPE values could range from 1500-1800 J/kg over parts of mainland Nova Scotia and central Newfoundland. Surface based convection is expected to initiate early this afternoon over the spine of Nova Scotia and central Newfoundland. The main risk with these storms will be heavy downpours (25-50mm), especially over Nova Scotia and central to northeastern Newfoundland where some training of thunderstorms may occur. There is also the risk of hail (1-2cm) and strong wind gusts.
Central Labrador will also continue to see come elevated embedded convection associated with an upper level low over northern Quebec. Locally heavy downpours and small hail are possible.
For southern marine areas, there are a couple of low pressure centers that are tracking from West Scotian Slope to the southern Grand Banks. Some isolated convection is expected to continue today. Some strong wind gusts to 30KT are possible under thunderstorms.
Regional Impacts
New Brunswick… Mainly southern New Brunswick could see lightning and locally heavy downpours.
Nova Scotia…Lightning, heavy downpours (25-50mm where training may occur), small hail and strong wind gusts.
PEI…Lightning, heavy downpours , small hail and strong wind gusts are possible.
Newfoundland…Lightning, heavy downpours (25-50mm where training may occur), small hail and strong wind gusts.
Labrador… Lightning, heavy downpours , small hail and strong wind gusts are possible.
Roberta McArthur
Convective Discussion
This could be a very active day for much of the Atlantic Provinces with the main focus of energy being over New Brunswick and possibly spreading into western PEI. In general there will be a weak surface trough from western Labrador then through New Brunswick which will help aid in the thunderstorm initiation. For most of the Maritimes there are high CAPE values between 1000-2000 J/kg and very high levels of moisture, this will lead to a high probability that heavy down pours will occur. Over Newfoundland and Labrador updrafts will be much weaker however with the high moisture content of the airmass locally heavy rain is still a possibility. Over New Brunswick the wind shear is sufficient to organize some storms, longer lived thunderstorms can be expected with a low chance of supercell and bow echo formation. Should stronger storms develop strong wind gusts 70-90 km/h and hail of 2-4 cm is possible.
Over Nova Scotia dynamics are not as favorable however there is a chance that back building thunderstorms could develop along the spine of nova scotia.
Regional Impacts
New Brunswick… Heavy Rain 25-50mm in heaviest thunderstorms, Hail 2-4 cm and wind gusts 70-90km/hr.
Nova Scotia… Heavy Rain 25 mm, locally higher amounts in back building thunderstorms.
PEI… Heavy Rain 25-50mm in heaviest thunderstorms, Hail 2-4 cm and wind gusts 70-90 km/hr over western areas possible.
Newfoundland and Labrador… Locally heavy downpours 20mm, small hail possible over western Labrador.
Convective Discussion
An upper ridge moving over the Maritimes will suppress the convection somewhat and may inhibit convective initiation till late in the day. Overall the CAPE values are quite favorable being greater than 1000 j/kg for most of the Region. 0 – 6 km Wind shear values are of 35-40 knots over NW NB and for Newfoundland this will increase the potential for organized convection over these areas. Over Newfoundland if convection occurs it will likely begin early this afternoon while the thermodynamics still remain strong. Over New Brunswick the probability of severe weather is low but it is possible that severe thunderstorms could advect from Maine late in the day.
Regional Impacts
New Brunswick…
A general risk of thunderstorms for most areas with a heightened risk of severe storms for northwest areas, local rain of 25mm. If severe thunderstorms develop they will be very late in the day as dynamics gradually become more favorable.
Nova Scotia…
A low risk of thunderstorms that could produce local rainfall amounts near 20mm. A slight risk of that multiple thunderstorms could move over the same area causing further amounts.
Prince Edward Island…
A low risk of thunderstorms that could produce local rainfall amounts near 20mm.
Newfoundland…
A low risk of thunderstorms that could produce local rainfall amounts near 25mm and wind gusts of 50-70 km/hr. A slight risk of that multiple thunderstorms could move over the same area causing further amounts.
Labrador…
There is a chance of thunderstorms embedded in the trough that is approaching from Quebec.
Mel Lemmon
