Amendment to Convective Outlook for August 30th, 2020

Convective Outlook Valid for Today and Tomorrow

Regional Impacts

 

Isolated thunderstorms with locally heavy downpours and gusty winds.

 

Convective Discussion

 

Thunderstorms can be expected for eastern New Brunswick… PEI… Northern Nova Scotia and into the Gulf of Saint Lawrence. There is some upper support with strong shear, however with low CAPE updrafts should remain weak. However given the favourable dynamics and warm water in the Gulf it is possible that some storms could become organised. Although unlikely strong surface sings could develop in some of these storms.

 

Thunderstorm Outlook for Day 1

 

 

Thunderstorm Outlook for Day 2

 

Convective Outlook Valid for Today and Tomorrow

Regional Impacts

 

Locally heavy downpours possible over southern New Brunswick and Nova Scotia.

 

Convective Discussion

 

In general weak updrafts can be expected today as warm advection aloft will tend to keep the local atmospheric conditions relatively stable. However we will continue to see ample moisture with upwards of 50mm of precipatable water available for southern areas and generally more than 40mm across the Maritimes. Embedded thunderstorms could be sufficient to generate local flash flooding this evening for southwest Nova Scotia and locally heavy downpours elsewhere. The threat of severe weather is minimal today, however conditions for tomorrow could be somewhat more hazardous depending on the remaining moisture and timing of the upper trough that will move over the region.

 

Thunderstorm Outlook for Day 1

 

 

Thunderstorm Outlook for Day 2

 

 

Convective Outlook Valid for Today and Tomorrow

Regional Impacts

A risk of isolated thundershowers over southeastern Labrador today.

A risk of some embedded thundershowers Saturday night across portions of western Nova Scotia.

 

Convective Discussion

A risk of thundershowers over SE LAB today associated with the upper low sitting over the area. SAT PIX does show some partial clearing which would help with some shallow CBs this afternoon. Highly doubt if anything will be observed near the coastal communities. Locally heavy downpours possible in some cells…if they develop.

 

A warm frontal trough will give the risk of embedded thundershowers Saturday night across portions of WRN NS. Heavy downpours would be the only threat.

 

Thunderstorm Outlook for Day 1

 

Thunderstorm Outlook for Day 2

 

Jeremy

Convective Outlook Valid for Today and Tomorrow

Regional Impacts: Thundershowers, rain and possible gusty winds up to 80 km/h are expected later today for the northern Gulf of St. Lawrence and the Northern Peninsula of Newfoundland. Small hail is possible as well.

 

Convective Discussion: Freezing levels are expected to be around 6500 feet and the equilibrium point is expected to be around 20,000 feet. So, low topped CB’s expected near the upper low. The low is vertically stacked from the sfc right up to 250 mb. So, not a lot of dynamics leading to severe weather. Just quite unstable due to cold air aloft and the water still quite warm. Cool air CB’s. In general, the winds are expected to be too strong for waterspouts since gales are expected.

 

Thunderstorm Outlook for Day 1

 

 

Thunderstorm Outlook for Day 2

 

Isolated t-shwrs are expected in Labrador tomorrow as the upper low pulls to the north. Convection is not expected to be severe since the upper low will starting to fill and the instability is no longer over the warm water.

 

Convective Outlook Valid for Today and Tomorrow

Thunderstorm Outlook for Day 1

 

Regional Impacts

Newfoundland: embedded TCus and Isolated thunderstorms giving mainly high rainfall amounts, exceeding 50 mm, combined with synoptic rainfall.

Southern Labrador: isolated to scattered thundershowers

Marine for southern Gulf of St. Lawrence, Cabot Strait and southern Gulf – Port au Port: Slight chance of waterspouts late this afternoon into this evening with gusts to gales possible.

 

Convective Discussion

A low over southern Labrador has a frontal trough extending southeast  to western Newfoundland. Ahead of the trough a strong southerly  jet extending from near the surface to midlevels is advecting significant moisture. While the tephi profiles are marginal at best, with low level capping,  lower level lift and moderate PVA, combined with some orographic forcing along the southern coast of the island, will give some enhance embedded TCus  and isolated CBs to enhance rainfall amounts. Winds will be brisk just with the synoptic forcing, and freezing levels are probably too high for anything significant.  For Labrador the situation is similar, but without the moisture feed. Almost moist adiabatic profiles with drying above 700 mb, with PWAT between `15-25 mm and southerly shear around 25 kts, argues  for isolated to scattered thundershowers with some gusty winds. With freezing levels near 5000 feet, small hail is definitely possible.

 

 

Thunderstorm Outlook for Day 2

 

 

Convective Outlook Valid for Today and Tomorrow

Regional Impacts

NB and PEI: for this afternoon numerous clusters of strong thunderstorms producing heavy downpours 25+mm, hail 1cm, and gusts between 60-90 km/h.

Newfoundland&Labrador: Very moist airmass with isolated embedded thunderstorms spreading throughout the province - producing rainfall amounts in excess of 50 mm.

 

Convective Discussion

Surface Low pressure over Lower Quebec North Shore with cold front extending southwestwards along the St. Lawrence Valley. A southerly low level jet is spreading moisture from the Gulf of Maine across NB to Western Labrador. While steady rain is expected over northern regions, multi-cellular thunderstorms will continue to develop ahead of the advancing cold front. The threat of these storms becoming severe is reduced over areas where showers and thunderstorms have already developed during the morning. The focus will now be over southernmost NB and PEI for the most robust storms, and the main threat will remain the possibility of EF0-1 wind damage.

 

Thunderstorm Outlook for Day 1

 

 

 

Thunderstorm Outlook for Day 2

Convective Outlook Valid for Today and Tomorrow

Regional Impacts

This afternoon until early evening: Isolated thundershowers over southern Labrador and central and eastern Newfoundland. Brief moderate showers with wind gusts between 50-70 km/h are possible.

Tonight: A few thundershowers over western and southern New Brunswick and western Nova Scotia. Brief heavier showers.

 

Convective Discussion

A number of weather features stand out this morning. The 500mb upper trough extends from the Labrador Sea to Northeastern Gulf of St. Lawrence, and a weakly cyclonic upper jet stretches from the Quebec North Shore to Southeastern Newfoundland. The cold air aloft more than makes up the limited surface heating and so a few cumulonimbus will develop this afternoon despite CAPE values between 250-500 J/kg. The airmass is drying nicely as open cellular pattern forming over the region. Weak downdraft could produce wind gusts between 30-40 kt.

 

A warm front will advance over the Maritimes tonight, but it will be quickly followed by a cold front advancing from Quebec Tuesday. Along the warm front some embedded non-severe thundershowers may touch westernmost areas.

Thunderstorm Outlook for Day 1

 

Thunderstorm Outlook for Day 2

Convective Outlook Valid for Today and Tomorrow

Regional Impacts

 

Newfoundland and Labrador: Slight risk for an isolated thundershower this afternoon over southeastern Labrador and northern regions of Newfoundland. Slight risk of embedded thundershowers overnight over the Gulf of St. Lawrence and southwestern Newfoundland.

 

Convective Discussion

 

An upper level feature over Labrador with a cold 500 mb trough slowly moving eastward will provide some instability in TCUs and showers for much of Labrador and northern Newfoundland today. Some brief heavy downpours are possible with cells that develop given freezing levels around 7000 ft and precipitable water of around 20 mm. A quick moving short-wave trough currently over central Quebec will swoop though northern Gulf of St. Lawrence overnight and over Newfoundland by Monday morning. There may be a slight risk for embedded convection in the morning hours.

 

Some TCUs in showers are expected this afternoon over northern New Brunswick. The 12Z Caribou sounding shows a sharp warm nose from 650 to 500mb and the convective temperature today is likely not going to be high enough to break that cap, thus no thundershowers are expected. A second short wave trough over southern Quebec this evening is expected to slide southeastward and some overnight convection along the warm front may clip western parts of the maritime marine district Monday morning.

 

Thunderstorm Outlook for Day 1

 

 

Thunderstorm Outlook for Day 2

 

Convective Outlook Valid for Today and Tomorrow

Regional Impacts

 

Labrador: Isolated non-severe thundershowers this afternoon. Locally heavy downpours and small hail will be the main threats.

 

Nova Scotia: Isolated non-severe thundershowers this afternoon mainly along the spine and towards the Atlantic coast this afternoon. Locally heavy downpours and moderate wind gusts will be the main threats.

 

 

Convective Discussion

 

An upper level low over the Labrador Sea with a trough extending southwestward into southeastern Labrador and the Lower North Shore Quebec will initiate some convection this afternoon and evening. There is some slight cooling aloft with orographic lift to aid in thunderstorm development. Southeastern Labrador could see CAPE values of around 400 J/kg with precipitable water around 20 mm. 0-6km shear is however quite low so cells that do develop could give some brief heavy downpours but would not last long. With freezing levels of around 7000ft, small hail is possible.  TCUs in showers are expected further west into western Labrador throughout the day where some slight warming aloft is expected to cap and further development.

 

A second trough extends from the Avalon Peninsula towards the Atlantic coast of Nova Scotia this morning. Some initiation is possible behind the trough given the daytime heating in clearing skies with the possible help of a sea breeze along the spine of Nova Scotia. The upper dynamics are not as favourable, however, with a warm nose at 700 mb to overcome and drier air moving in behind the trough. If cells initiate they should move in a west/northwest direction toward the Atlantic coast and fizzle by the evening. Precipitable water is in the mid 20s and some moderate mainly uni-directional 0-6km wind shear near 40KT could keep cells that initiate going with some locally heavy downpours and moderate wind gusts possible. As this trough continues further south into the Maritime slope waters, the warmer surface temperatures as well as any convective cloud top cooling could initiate overnight convection for tomorrow morning. CAPE values in excess of 1000 J/kg and moderate 0-6km shear will help in organization of a possible organized line over East Scotian Slope and Laurentian Fan.

 

Thunderstorm Outlook for Day 1

 

 

Thunderstorm Outlook for Day 2

 

Instability associated with a cold pool dropping in from Hudson Bay and low pressure over Labrador could initiate some convection over central Labrador and into northern Newfoundland tomorrow. A short-wave trough will be moving into the Maritimes from southern Quebec tomorrow which could have some embedded convection associated with it as it tracks across southern New Brunswick into Nova Scotia overnight into Monday morning.

 

Convective Outlook Valid for Today and Tomorrow

Regional Impacts

 

Newfoundland: Isolated thundershowers for western Newfoundland stretching eastward during the evening across the Island.

Labrador: Slight risk for an isolated thundershower over southeastern coastal regions.

New Brunswick: Isolated non-severe thunderstorms today for southern and western regions.

 

 

Convective Discussion

 

A slow moving upper level low resides over eastern Labrador stretching into the Labrador Sea. Some convection may ignite near the low centre today over southeastern coastal areas of Labrador today. A trough extending from Anticosti southwest towards the eastern townships in Quebec will move eastward today to lie over western Newfoundland towards southern New Brunswick this evening.

 

Areas of western Newfoundland could see some enhanced dynamics with the left exit of an upper level jet, combined with an approaching 500mb cold pool to help destabilize the environment ahead of the trough for late this afternoon into the evening and overnight hours. There is not much moisture with around 15 mm of precipitable water but decent uni-directional shear of 35KT could maintain convection with CAPE values between 200 and 500 J/kg. Some cloud-top cooling could maintain what may develop as it moves over western Newfoundland towards the east overnight.

 

Due to the quite cool area aloft over the Gulf of St. Lawrence, and decent uni-directional shear, there could again be a very slight risk of a waterspout develop over areas of eastern Anticosti, Gulf-Port-Au-Port, and Northeast Gulf marine areas this afternoon and evening.

 

Areas of southern Maine extending into southwestern New Brunswick will benefit from some enhanced upper level dynamics being in the area of the right entrance of an upper-level jet. A cold 500mb trough extending over central Maine combined with some warming at 850mb will help to overall destabilize the atmosphere. The only issue is the amount of rain and cloud moving through the area this morning, prohibiting much in the way of surface-based heating and areas over northern New Brunswick will likely not be able to break the warm cap at 700mb. Precipitable water values of 25-30mm over Caribou would suggest that some decent downpours are possible, but with strong 0-6km shear at 55KT a relatively strong flow aloft, cells would not likely see high rainfall rates for long. CAPE values also remain fairly weak at less than 250 J/kg. Some drier air between 700 and 500mb could mean some medium to strong downdrafts are possible and this will be the main concern with convection that develops this afternoon.

 

Thunderstorm Outlook for Day 1

 

 

Thunderstorm Outlook for Day 2

 

Convective Outlook Valid for Today and Tomorrow

Thunderstorm Outlook for Day 1

 

Regional Impacts

 

Southeastern Labrador: Isolated non-severe thundershowers.

Eastern Gulf of St. Lawrence: Gusty winds and possible waterspouts this afternoon into this evening.

Newfoundland: Generally isolated to scattered non-severe thundershowers. For northeastern regions possible wind gusts to 90 km/h and rainfall amounts reaching 25 mm/h locally.

 

Convective Discussion

A trough crossing the Gulf towards Newfoundland, with a cold trough at 700 mb giving some enhanced instability, along with la left exit region currently east of Deer Lake eastwards towards Ganer, will give some strong updrafts. Moisture is modest with PWAT around 20-25 mm, but shear is in the 25-30 kt range. Profiles and the upper air analysis shows fairly dry air from 850 mm and up, combined with the destabilisation associated with the approaching upper cold trough, and should give some healthy downdrafts. Rainfall amounts under individual cells have a slight possibility to reach 25 mm/h with the fairly brisk speed of the individual cells, but some training may boost the amounts to warning levels.

 

The same cold upper trough over waters in the eastern Gulf near or exceeding 20 C, with a unidirectional strong flow up to or exceeding 850 mb, may give waterspouts this afternoon into this evening. For the Newfoundland coast SSTs are slightly cooler, especially north of Corner Brook and Gros Morne, but have more potential offshore for southern Gulf – Port au Port.

 

 

 

 

Thunderstorm Outlook for Day 2

 

A weak east-west trough dropping south over New Brunswick may produce some thundershowers with a possibility for high wind gusts late in the day. For Newfoundland there is a possiblilty for non-severe isolated thundershowers for the middle of the west coast east to the Baie Verte Peninsula.

 

Convective Outlook Valid for Today and Tomorrow

Regional Impacts

 

Some weak thunderstorms are likely to develop late today over northern New Brunswick. This evening and tonight the risk will spread through the gulf impacting western Newfoundland by the morning..

 

Convective Discussion

 

The atmosphere will continue to destabilize later today and through tonight as a cold upper trough makes its way through the region. Overall the amount of moisture has diminished over the last few days but steepening lase rate should be sufficient to generate stronger updrafts overnight and tomorrow morning for the eastern gulf waters and tomorrow afternoon for parts of Newfoundland.

 

For tomorrow deep shear and CAPE will continue to increase as the upper trough approaches, with ~40 knots of 0-6km shear and ~1000 j/kg. Organised convection is possible with a low probability of supercell formation. Strong wind gusts, 25mm + rain and small hail is possible.

 

 

Thunderstorm Outlook for Day 1

 

 

Thunderstorm Outlook for Day 2

 

Convective Outlook Valid for Today and Tomorrow

Regional Impacts

For New Brunswick… local downpours of 20mm are possible for northwestern areas, however should organized thunderstorms develop possibly more.

 

For Northern Nova Scotia and southern Newfoundland… embedded thundstorms with weaker updrafts possible, some locally heavier rainfall could occur.

 

Convective Discussion

 

Today the vertical velocities should not be overly strong but despite this there is still a decent amount of moisture available with 30 + mm of precipitable water from the Sept-Iles and Caribou soundings. For today some locally heavy downpours and training of thunderstorms is possible and stronger returns are already showing up in Maine this morning. With daytime heating this should intensify further for western areas of New Brunswick into the afternoon.

 

Thunderstorm Outlook for Day 1

 

 

 

For tomorrow falling heights and increasing shear along with lowering freezing levels could lead to a larger hail potential and gusty surface winds.

 

Thunderstorm Outlook for Day 2

 

Convective Outlook Valid for Today and Tomorrow

Regional Impacts

 

No impacts due to thunderstorms are expected today.

 

Convective Discussion

 

Most of the deep convection today will remain to the west and to the south as an upper thermal ridge will suppress the deeper thunderstorm for the Atlantic Region. Solar insolation will kick in over new Brunswick and TCUs will quickly develop but the storms should not be deep enough to generate thunderstorm activity, although intense showers may be possible. Over the marine area large, heavy rain producing storms can be expected, with respectable deep shear of about 30 knots and CAPE values > 1000 j/kg some organised storms could develop.

 

Thunderstorm Outlook for Day 1

 

 

Thunderstorm Outlook for Day 2

 

Convective Outlook Valid for Today and Tomorrow

Regional Impacts

Slight risk of a thunderstorm giving brief moderate downpour for Valley and Central NS, PEI, and southern NB.

 

Convective Discussion

Some instability is expected this afternoon but it will manifest itself mostly in the low levels (below 3000m). Precipitable water range from 25-32 mm over southern portions of the Maritimes – hence the possibility of a brief downpour from towering clouds. Some regions have slightly higher dewpoints, and some will experience more surface heating from the sun - this greater instability could lead to the development of isolated thunderstorms.

 

Large high pressure cell over northern Quebec giving stable and dry air mass over Newfoundland and Labrador. Available energy is 0, and the precipitable water is an anemic 9mm at Stephenville.

 

 

Thunderstorm Outlook for Day 1

 

Thunderstorm Outlook for Day 2

 

Convective Outlook Valid for Today and Tomorrow

Regional Impacts

 

NS/NB/PEI/NFLD: Chance of a thundershower this afternoon.

Labrador: None.

 

Convective Discussion

 

Afternoon, surface based convection is possible today. Especially in areas where offshore northeast winds give convergence with onshore sea breezes. Precipital water is 20-30 mm so local downpours are likely. Dry mid layers will allow possible wind gusts and low freezing levels of 10,000 feet may allow small hail. The cape is generally low (300-400 J/kg) and the sheer is 20-30 kts so any storm develop will be mostly pulse in variety.

 

Thunderstorm Outlook for Day 1

 

 

Thunderstorm Outlook for Day 2

 

Convective Outlook Valid for Today and Tomorrow

Regional Impacts

 

NS/NB/PEI: None

NFLD: A chance of severe wind gusts and downpours this afternoon.

Labrador: Elevated convection giving downpours.

 

Convective Discussion

 

Elevated convection giving downpours is possible in Labrador. Precipital water is 30 mm there and it is in the region of the left exit of a 100 kt jet which is giving it support. Over eastern regions of Newfoundland surface based convection will initiate this afternoon. Precipital water is 40 mm and dry mid layers will allow possible wind gusts to 80 km/hr. A high freezing level of 13,000 feet will limit possible hail size. The sheer is a relatively low 20 kts or less so storms will be mostly pulse in variety.

 

Thunderstorm Outlook for Day 1

 

 

Thunderstorm Outlook for Day 2

 

Convective Outlook Valid for Today and Tomorrow

Regional Impacts

There is a slight risk of an isolated severe thunderstorm or 2 across central areas of New Brunswick this afternoon into this evening giving torrential rainfall and strong winds. Small hail is also a possible in the stronger cells.

Scattered thundershowers are likely for southeastern Labrador and western Newfoundland today and into tonight. This is mostly elevated precipitation so just some heavy downpours are expected.

There is a slight risk of a thundershower this afternoon and early this evening across the valley and northern Nova Scotia.

Lastly isolated thundershowers are possible for western Labrador later today.

 

Convective Discussion

The same front that produced some severe weather in Quebec yesterday is now situated across central areas of New Brunswick (though in a somewhat weakened state). The 12Z KCAR profile does support MLCAPE of 800-1000 j/kg, PWAT around 44 mm and good shear at around 40 knots. And also good low level instability. There are 2 warm noses that could prevent things from firing. However given enough buoyant energy, a diffluent flow at 500 mb observed at 12Z and a jet streak at 250 mb placing the region in the left exit region, isolated severe storms are a possibility.

 

An upper level feature will give some scattered thundershowers to SE LAB and WRN NL but all non-severe.

 

For the valley and northern NS there is a slight risk of a thundershower this afternoon and evening…but the limiting factor will be the upstream cloud cover now entering the region and lack of any trigger. Expect mostly TCU giving locally heavy downpours.

 

An approaching upper-level trough over north-central Quebec will give some isolated non-severe cells to western LAB later today.

 

Thunderstorm Outlook for Day 1

 

Thunderstorm Outlook for Day 2

 

Jeremy

Convective Outlook Valid for Today and Tomorrow

Regional Impacts

There is a risk of thundershowers this afternoon and evening across western and central Labrador. These could advect eastward affecting portions of the LAB coast tonight as well. Brief heavy downpours and gusty winds are possible.

There is a slight risk for a severe thunderstorm across the far northwest of NB. The main threat would be torrential rainfall…however strong wind gusts are also a possibility.

Lastly, there is a risk of isolated thundershowers this afternoon across the valley and northern NS. Torrential rainfall is the main threat.

 

Convective Discussion

The main focus today will be to see what forms upstream across southern Quebec and northern Maine. What will be a moot point today is a trigger. The KCAR tephi has ~ 25 knots of shear, PWAT of around 40 and MLCAPE of 1000-1200 j/kg. There is a moist tongue near the surface which would add to the buoyancy as the day progresses. The deep layer trough at 500 mb is further upstream at 12Z, but that should propagate eastward today, resulting in an increase in wind shear across NW NB. If cells do make it to the region, torrential downpours and gusts to 70-80 km/h would be expected. Will have to monitor the upstream development this afternoon and the evolution of movement.

 

For Labrador, where shear is 40-45 knots, and closer to the surface and upper trough, scattered cells are likely. Then only issue would be warm air aloft…however given the dynamics that would be broken fairly easily. Brief heavy downpours and gusty winds are possible with the storms.

 

There is a risk of isolated non-severe thunderstorms across the valley and northern NS this afternoon. There is very little shear (YQI and GYX showing 20 knots), but the PWAT is 40+. CAPE looks to be in the 500-1000 range. Locally torrential downpours will be the threat.

 

Thunderstorm Outlook for Day 1

 

Thunderstorm Outlook for Day 2

Convective Outlook Valid for Today and Tomorrow

Regional Impacts

 

NB/NS/PEI/Labrador:  No significant impacts expected.

 

Newfoundland: Slight risk of short lived thunderstorms over central and eastern Newfoundland.  Main threat is local heavier showers and gusty winds. 

 

Convective Discussion

 

An area of PVA is currently bringing some showers and thundershowers just southwest of Newfoundland.  This area of PVA along with cooler upper atmosphere temperatures and high insolation will bring some thundershower activity to parts of Newfoundland today.  Wind shear is low so long lived severe thunderstorms is not expected.  Precipitable water is low as well so torrential downpours are not expected.  Still, there is a low potential for short lived severe storms bringing localised heavy rainfall and gusty winds mainly over eastern Newfoundland.  Prog tephis over eastern Newfoundland showing between 500 to 1000 J/kg with low shear and low precipitatble water.

 

Thunderstorm Outlook for Day 1

 

Thunderstorm Outlook for Day 2

 

 

Barrie MacKinnon

 

 

Convective Outlook Valid for Today and Tomorrow

Regional Impacts

 

For Labrador.. Small hail and gusty winds in thunderstorms this afternoon and this evening. Heavy downpours may occur.

 

For New Brunswick.. Isolated thunderstorms possible over norther New Brunswick this afternoon. No Severe Weather expected. Small Hail possible.

 

Convective Discussion

 

Labrador continues to be a main threat area today with an upper trough progressing eastward through northern Quebec. Aloft at 250 there isn’t strong support but the dynamics are somewhat more favourable as you move down through the atmosphere. Good low level shear below 500 mb could favour the development of organised thunderstorms this afternoon, possible affecting western Labrador late this afternoon and early in the evening.

 

Not much is expected southward in New Brunswick with somewhat dry, relatively speaking,  lower levels and upper lapse rate that are not overly conducive to deep convection. However an upper trough may act to destabilize the atmosphere allowing for daytime heating and surface convergence near the northern coastlines to trigger some convection.

 

Thunderstorm Outlook for Day 1

 

 

Thunderstorm Outlook for Day 2

 

Convective Outlook Valid for Today and Tomorrow

Regional Impacts

 

NS/NB/PEI/NFLD/Labrador: None

 

Convective Discussion

 

Lower dew points and a stable airmass has moved into the area. There is a thundershower risk for southern Maritime marine areas today.  On Saturday there is a thundershower risk for NW New Brunswick and parts of Labrador as separate surface troughs move across those regions.

 

Thunderstorm Outlook for Day 1

 

 

Thunderstorm Outlook for Day 2

 

Convective Outlook Valid for Today and Tomorrow

Regional Impacts

 

NS/NB/PEI/NFLD: None

Labrador:  A risk for most regions and a chance of gusty winds and hail southeast.

 

Convective Discussion

 

A low pressure system will track across Labrador today. Ahead of the low, daytime heating will allow temperatures to reach 27 degrees. Modifying the upstream sounding at Sept-Iles yields precipital water of 25- 30 mm, cape of 1000 J/kg and unidirectional shear of 30 kts. Additionally the freezing level is fairly low at 9,000 feet.  An upper level jet will approach this afternoon and southeastern Labrador will be in a favourable area of enhanced lift (left exit). The low freezing levels and decent cape above -10 C will support hail growth. The dry mid levels will support possible wind gusts.

 

Thunderstorm Outlook for Day 1

 

 

Thunderstorm Outlook for Day 2

 

Convective Outlook Valid for Today and Tomorrow

Regional Impacts

Risk of  thunderstorms over Northern and Western NB this afternoon, main threat is gusty winds and brief downpours.

Some thunderstorm activity is expected over central Quebec this afternoon and evening, some of these storms may propagate to western Labrador late evening and after midnight

Convective Discussion

This morning, an upper ridge with stable dry conditions prevails over NF, while a cold trough extends from an upper low south of James Bay to southern Quebec. The area with the highest potential for convection is central and southern Quebec and northern Maine. Convective initiation should be fairly easy to attain given the buoyancy of this airmass. Using the most recent Maniwaki sounding, mean layer energy should easily reach 750-1000 J/kg - and with deep layer shear values of about 25kt – this will be adequate to sustain more robust isolated storm cells. Behind the remnants of Isaias, there is a marked drop in moisture content, so the main threat with these storms would be moderate to strong wind gusts.

Thunderstorm Outlook for Day 1

 

Thunderstorm Outlook for Day 2

Convective Outlook Valid for Today and Tomorrow

Regional Impacts

Chance of an afternoon thunderstorm – producing brief downpour and moderate wind gusts - over southern NF.

Convective Discussion

Very moist airmass prevails over NF this morning with a fair amount of potential energy, however mid-level lapse rate continue to be unfavorable for the development of deep convection. The area to focus would be over the southern third of the island where sunshine could help boost surface temperatures to values required for convective initiation, at this point the likelihood remains very low. Having said that, the upper jet (100+kt) may be too strong, shredding any developing towers. Elsewhere across the Atlantic provinces, fair conditions are expected under an upper ridge.

Thunderstorm Outlook for Day 1

Thunderstorm Outlook for Day 2