Day 1 Convective Outlook for Atlantic Canada Valid August 31, 2019

Convective Discussion

No thunderstorm activity expected.

Regional Impacts

Maritimes…

None.

Newfoundland and Labrador…

None.

Andy Firth

Day 1 Convective Outlook for Atlantic Canada Valid August 30, 2019

Convective Discussion

A cold front will approach western Labrador today. There is a slight risk of thundershowers late this afternoon.

Regional Impacts

Maritimes…

None.

Newfoundland and Labrador…

Risk of thundershowers for western Labrador.

Andy Firth

Convective Outlook Valid for August 27 2019

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 Outlook Valid for August 26 2019

Convective Discussion

Nothing expected for the Maritimes nor Newfoundland and Labrador land areas.

Basically, there is a large and deep ridge over Atlantic Canada, with a strong subsidence inversion pushing well south over the Scotian Shelf and the Grand Banks. There are other inhibiting factors, including low moisture and very low shear over most regions, but the inversion is the real killer. On Tuesday there is a slight chance of convection along southernmost areas of Newfoundland, and a lesser chance for Cape Breton.

For the marine areas to the south, there is a chance of convection, due to a small low moving up slowly  from south of the Scotian Shelf towards southwestern Newfoundland. Currently there is some convection mainly east and south of the low, with some surface based convection near and south of the warm front. As the low moves north over colder water, this will diminish, and there will be occasional embedded convection as it moves up tonight, again near and south of the warm front.

Regional Impacts

Atlantic Provinces: none today or tonight.

Southeastern offshore waters: non-severe thunderstorms over southernmost waters slowly moving north and weakening, mainly for Laurentian Fan and the southwestern Grand Banks. For southernmost waters of Laurentian Fan the Southwestern Grand Banks gusty winds are possible with CAPEs near 500 J/kg for southernmost Laurentian Fan and somewhat higher for the southern half of the Southwestern Grand Banks where it ranges from 500 to 1000+ J/kg.  Otherwise local downpours are fairly likely, with precipitable water near 50 mm in the south. Again. Convection will become embedded and weaken as the low moves north.

Doug Mercer

Convective Outlook Valid for August 25, 2019

Convective Discussion.

 

No activity expected in the region today.

 

Regional Impacts.

 

Nil.

 

 

Jeremy

Convective Outlook Valid for August 24, 2019

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 Outlook Valid for August 23, 2019

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 Outlook Valid for August 22 2019

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 Outlook Valid for August 21 2019

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 Outlook Valid for August 20th, 2019

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 Outlook Valid for August 19th, 2019

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 Outlook Valid for August 18, 2019

Convective Discussion.

Early morning convection across southwestern NB has weakened and will continue to weaken this morning. There were a couple embedded TSRA, but increasing stability will negate any more CBs. The only area where cells are possible are across ERN LAB. Adjusting the surface temp to around 26 from YYR gives close to 500 J/kg. A surface trough will act as a trigger this afternoon. Sat pix shows some decent clearing across the region as well. Precipitable water is fairly low, but freezing levels are low and the shear is modest at around 35 knots or so. Expect some gusty winds and possible small hail in a couple of the cells. Elsewhere no convection is expected in Atlantic Canada.

Regional Impacts.

Labrador: scattered TS this afternoon giving gusty winds and possible small hail for ERN regions.

Nova Scotia/New Brunswick/PEI/Newfoundland: nil.

Jeremy

Convective Outlook Valid for Augut 17 2019

Convective Discussion

No severe impacts expected. Highest chance for convection for Labrador from the west to the  Mid Labrador coast. A slight chance for Newfoundland this afternoon, and a chance for a thundershower to move into westernmost New Brunswick.

For Labrador a trough extending from Hudson Bay to the Mid Labrador Coast, combined with an upper jet over northern Labrador, with a right entrance near the trough axis, will give some support for lift. As the upper jet moves east this afternoon, so will the instability . Moisture isn’t great, with precipitable water in the 15-25 mm range. CAPEs are on the low, with the highest expected less than 500 J/kg,  with the highest amounts at the southern edge of the threat zone. Also shear is marginal at about 30 kts. Expect a few thundershowers with some moderate wind gusts. The freezing level is near 9000ft, so small hail is possible.

For Newfoundland there is little dynamic forcing. The there is a weak upper trough moving through, followed by weak ridging from mid-levels up, and an associated weak upper jet. The main forcing mechanism will be daytime heating, and some moisture. The 12Z tephigram from Stephenville was less stable than model guidance, and with a forecast high near 25 C and a dewpoint near 13 C, a parcel lift gave a CAPE around  300-400 J/kg. Based on this there is a chance for isolated thundershowers this afternoon, with some gusty winds.

Regional Impacts

Labrador: Occasional non severe thundershowers with some gusty winds and a chance for small hail.

Newfoundland: a possibility for isolated  thundershowers this afternoon.

New Brunswick: a slight chance for thundershowers this afternoon in the extreme northwest, but only if the cloud breaks up today.

Doug Mercer

Convective Outlook Valid for August 16th, 2019

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 Outlook Valid for August 15th, 2019

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 Outlook Valid for August 14th, 2019

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 Outlook Valid for August 13th, 2019

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 Outlook Valid for August 12th, 2019

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

Day 1 Convective Outlook for Atlantic Canada Valid August 11, 2019

 

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

Day 1 Convective Outlook for Atlantic Canada Valid August 10, 2019

Convective Discussion

There is a chance of thundershowers over most of Atlantic Canada today. Throughout the region there is cold air aloft and freezing levels are 10,000 feet or less due to the existence of a large upper trough. In addition there is a shortwave just west of the Maritimes at 12Z this morning. There is also a cold trough at 500 mb just west of the Maritimes as indicated by 12Z soundings. There is plenty of sunshine throughout the region for the convective temperature to be reached this afternoon. The southern Maritimes is also in the left exit region of a 250 mb Jet.

Over NS and southeastern NB, shear values are forecast to be unidirectional from the southwest and near 30 knots in the 0-6km layer. CAPE values are forecast to be near 1000 J/kg over these areas. These are the areas highlighted in yellow, where there is a chance of severe thunderstorms today with strong wind gusts and possible hail. The lapse rates are steep between 850 and 700 mb over these areas contributing to strong buoyancy and also of potential for significant DCAPE giving strong wind gusts. The low freezing levels will contribute to the risk of small to medium sized hail.

Elsewhere, CAPE’s and shear are less, so thundershowers that form should not be severe.

Regional Impacts

Maritimes…Thundershowers, heavy downpours, hail and strong wind gusts are possible today. Severe thunderstorm watches may be issued for portions of the area denoted in yellow.

Newfoundland and Labrador…Risk of thundershowers for Newfoundland today or tonight. Risk of thundershowers for central/eastern Labrador.

Steve

Day 1 Convective Outlook for Atlantic Canada Valid August 9, 2019

Convective Discussion

A cold front will move across the Maritimes this afternoon and evening. A diffluent upper flow and dropping heights will favour the development of severe weather ahead and near the front. Cape values of 1000-1500 J/kg and uni-directional shear of 30-40 knots is being indicated by the 12z soundings. Skies are clearing and the fog patches lifting in the wake of last night’s rain system, so daytime heating to 25-28 degrees is very possible. CU/TCU/CB formation is expected to develop shortly after noon. This system gave numerous reports of wind damage through New England on Thursday so that is likely the biggest concern. Dcape values are indicating 90-100 km/h gusts.  Hail and torrential downpours are also possible. The precipital water is 30-35 mm. The freezing level is near 12,000 feet but there is good Cape through the hail growth zone. Oddly enough the main upper jet is well ahead of the surface cold front so not sure if the dynamics from that will play a part or not.

Regional Impacts

Maritimes…

Thundershowers, torrential downpours, hail and strong wind gusts are possible today. Severe thunderstorm watches will be issued for the area denoted in yellow.

Newfoundland and Labrador…

Risk of thundershowers for western Newfoundland tonight.

Andy Firth

Day 1 Convective Outlook for Atlantic Canada Valid August 8, 2019

Convective Discussion

A trough of low pressure and an associated upper jet will approach from the west today. Over the Maritimes embedded/non-surface based thundershowers are possible with the associated area of cloud and rain this afternoon and/or tonight.  Over western Labrador, surface based thundershowers are possible this afternoon and into the evening ahead of the approaching area of cloudiness. The energy is weak and the shear is minimal so just a risk is expected.

Regional Impacts

Maritimes…

Risk of thundershowers.

Newfoundland and Labrador…

Risk of thundershowers .

Andy Firth

Convective Outlook Valid for August 7, 2019

Convective Discussion

Today there are three things going on. For Labrador a combination of a surface low under a weak diffluent upper  jet will give non-severe thunderstorms which may persist into this evening. For New Brunswick air-mass thundershowers are possible ahead of a slowly approaching low, with a southerly flow brining in an axis of moisture up to al least 700 mb. Finally there is a low crossing the scotia shelf and giving embedded thundershowers.

For Labrador the upper trough moving in from the west is diffluent with a weak jet on the south side. Shear is around 25-30 kts, with CAPEs possibly reaching 500 J/kg, but more likely less.

Dewponts will increase slightly this afternoon, and if they reach 16 C, the 500 CAPE may occur. Downdrafts are possible, but shouldn’t be more than 60- kph.

For western New Brunswick, surface to 700 mb dewpoints are increasing and may reach 17+ C from he surface, and good insolation is expected early this afternoon with mainly clear skies in the northwest. PWATs are healthy and between 30-40 mm. Shear is low, arguing for airmass pop-ups. The only worry is the slow speeds of the potential thundershowers, which may give 25 mm/hr.

Regional Impacts

New Brunswick: mainly a chance of  non-severe thundershowers into this evening, with a chance for local downpours near or possibly exceeding 20 mm.

Labrador: a chance of non severe thundershowers, with showers up to 15-20 mm and some gusty winds.

Southern Waters: Embedded thundershowers with occasional gusty winds.

Doug Mercer

Convective Outlook Valid for August 6, 2019

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 Outlook Valid for August 5, 2019

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 Valid for August 4, 2019

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 Outlook Valid for August 3, 2019

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 Outlook Valid for August 2nd, 2019

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 Outlook Valid for August 1st, 2019

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