Convective Outlook Valid for Today and Tomorrow

Regional Impacts

For the Maritimes: Scattered TCU/CBs will develop after lunch in association with an trough of low pressure. Non-severe but some gusty winds are possible over NS and small hail in NB.

For Newfoundland: scattered CBs are occurring now in the southwest and these pulses of precipitation will continue to track northeastward, with likely a weakening trend in the lightning. Heavy downpours can be expected.

 

Convective Discussion

The same upper low that was responsible for the severe weather in the Maritimes yesterday is still kicking around, and is located near the Gaspe Peninsula. The morning activity is a result of PVA/vort max noted in SAT imagery. There were some good winds with the cells over portions of the MRTMS but there is a weakening trend in that. Locally heavy downpours for Newfoundland today with 20+ mm possible in one hour or less. I don’t think there will be much of a wind gust based on the 12Z YJT tephi…maybe some gusts to 60 km/h.

 

As skies are clearing over the MRTMS expect scattered TCU/CBs to begin forming, though severe weather is not anticipated. If the timing was 3 hours different we could be looking at isolated severe storms across Nova Scotia. Both the YQI and YAW tephi has around 50 knots of shear, good lapse rates, and CAPE between 750 and 1000. However, the upper trough is sliding southward, so the shear is diminishing which should negate the severity of the CBs. KCAR tephi has only 15 knots of shear, so that will give one an indication of the weakening of winds aloft. All in all we expect SCT TCU/CBs across the MRTMS giving locally heavy downpours (PWAT roughly 30 mm) and small hail in the stronger cells. We could have gusts to 70 km/h across NS in the stronger cells.

 

For Saturday: a slight risk of a thundershower across northern and eastern NS, as well as Cape Breton. Newfoudland looks to have potential for numerous, small TCU/CBs (short-lived given the very weak flow). Heavy downpours and small hail are likely…for south/central regions, as well as the Avalon Peninsula.

 

Thunderstorm Outlook for Day 1

 

Thunderstorm Outlook for Day 2

 

Jeremy

Convective Outlook Valid for Today and Tomorrow

Regional Impacts

New Brunswick, PEI, valley and northern Nova Scotia: There is a risk of severe thunderstorms today giving heavy rainfall, strong winds and small hail. Currently some storms producing heavy rain across northern NB. A few thunderstorms should form early this afternoon across the south. Scattered thunderstorms should develop later this afternoon across NS that could advect into PEI .

Southwestern Labrador: slight risk of a thundershower this afternoon and evening.

East of the Avalon: isolated elevated thundershowers.

 

Convective Discussion

There is a fairly decent chance in seeing some severe thunderstorms today across New Brunswick, Nova Scotia and PEI today giving heavy rain, strong winds and hail. There is a strong 250 jet placing the favourable areas in the left exit region, as well as some divergence. Divergence is also evident at 500 mb as the upper trough slowly approaches from the west, so heights will be falling a little as well. There is not as much low-level moisture as yesterday but still enough to add to the buoyant atmosphere. The 12Z KCAR tephi has a decent unstable profile, PWAT of 36 mm, a relatively low FZLVL (around 10,ooo feet) and about 35 knots of shear. The current storms affecting the northern half of NB is giving locally heavy rainfall. Modifying the sounding gives a mixed layer CAPE of around 1000. Mind you the shear will be decreasing through the day across northern NB, it will remain across southern NB, so strong storms giving wind gusts of around 80 km/h, heavy rain and hail of up to 2 cm are possible. For Nova Scotia, the issue right now in the favourable zone (valley and northern areas) is the mid level cloud cover. The 12Z YQI tephi has decent low-to-mid level lapse rates and shear of up to 35 knots. PWAT is the same as KCAR. Modifying it for a temperature of 31 degrees gives close to 1000 CAPE. So, much like NB there is a decent chance in seeing severe storms. The issue, as mentioned above is the current cloud cover. There is a back edge moving into the Gulf of Maine so I would expect cells to develop later this afternoon. Again heavy rain, strong winds and small hail are possible in the stronger storms. Some of these cells across southern NB and NS should progress into PEI later today.

 

A slight risk of a thundershower this afternoon and evening near Wabush/Labrador City  in the vicinity of the upper low.

 

Thunderstorm Outlook for Day 1

 

Thunderstorm Outlook for Day 2

 

Jeremy

Convective Outlook Valid for Today and Tomorrow

Regional Impacts

For Nova Scotia: there is a slight risk of a severe thunderstorm across portions of the eastern mainland into early this evening. The main threat is heavy rainfall. Some gusty winds are also possible but below warning threshold (90 km/h).

For New Brunswick: scattered thunderstorms are expected to develop this afternoon.

For Newfoundland: there is a risk of isolated elevated/nocturnal  thundershowers tonight

 

Convective Discussion

As mentioned above, there is a slight risk of a severe thunderstorm across the eastern mainland of Nova Scotia this afternoon. Looking at the parameters (MIST): we have the moisture with dewpoint temperatures into the low 20’s and a moist tongue at 850; the instability is there with model LI’s in the minus 5 to minus 8 range; analysis from the 12Z YQI and YAW tephis show 30-40 knots of shear in the 0-6 km level; and lastly a weak trough offering up a trigger mechanism once the convective temperature is reached early this afternoon. Upper air analysis doesn’t show much at 250 mb as the main jet is well to the north of NS. There is a 40 knot jet at 500 mb, but not really an indication of at least minimal falling atmospheric heights. The upper level trough at 500/700 is well to the west and won’t be a factor until D2 as it approaches Maine and New Brunswick. One thing noted on the 12Z tephis is the warm, stable air aloft. This will be the determining factor. Modifying the 12Z soundings for temperatures of 30, and dewpoints of 22 gives about 1000 mixed-layer CAPE. The MUCAPE is way overdone and ignored. I expect TCUs to form shortly after the lunch hour with isolated-to-scattered TS not long thereafter. Once again, the stability aloft may prevent any potential cells from becoming severe (25+ mm of rain in one hour).

 

Scattered cells are likely to develop across northern New Brunswick this afternoon…there is a very little chance in seeing anything close to severe limits. Locally heavy downpours can be expected.

 

Lastly, there is a risk of elevated convection tonight across southern Newfoundland.

 

Thunderstorm Outlook for Day 1

 

Thunderstorm Outlook for Day 2

Convective Outlook Valid for Today and Tomorrow

Thunderstorm Outlook for Day 1

 

Regional Impacts

New Brunswick: Heavy downpours for most of the province likely, with strong downdrafts and possibly a wet microburst. The main threat area is the southwest.

Nova Scotia: Poissibly a similar situation to New Brunswick, but mainly for the Cobequids and the west inland for the worst impacts.

Prince Edward Island: Scattered thundershowers possible, with local heavy showers and gusty winds.

 

Convective Discussion

There’s a cold front from north of the Gaspe and extending southwest over northwestern Maine, slowly moving in this afternoon . There’s ample low moisture in the warm sector with PWATs near 45 mm, a moist tongue over southern New Brunswick, and a dry layer at 700 mb near and behind the cold front. Bulk shear is 40+ kts, but there is little storm relative helicity. This argues for multicells with the front as an organising feature.  There’s already some weak prefrontal lines approaching the northwest, and conditions should intensify this afternoon, with some cooling aloft as a thermal ridge moves east of the porvince and we get some daytime heating. A diffluent flow aloft associated with an upper low to the northwest should also help.

 

For Nova Scotia conditions will occur later this afternoon or this evening with the approach of the low. Conditions should moderate into this evening.

 

 

 

Thunderstorm Outlook for Day 2

 

 

Convective Outlook Valid for Today and Tomorrow

Thunderstorm Outlook for Day 1

 

Regional Impacts

New Brunswick and western Nova Scotia: Depending on cloudiness, possibility of thunderstorms east and severe thunderstorms west, with heavy downpours the greatest threat, followed by gusty winds.

Northern Newfoundland and southeastern  Labrador: chance for non severe thunderstorms,

 

 

Convective Discussion

The synoptic situation is similar to yesterday, with a low near Hudson Bay and a second over the Labrador Sea, with an extended east-west trough between them and over Labrador. This also produces slight ridging over Quebec and New England.  For Newfoundland and Labrador there is some support for non-severe convection near the Strait of Belle Isle.  Some weak PVA from a jet right exit, combined with daytime heating may give a few cells. PWAT is only about 20 mm., but CAPEs in excess of 200 J/kg with a slight chance of 500 J/kg are possible.  Gusty winds and brief heavy showers are the main issues, with a slight chance for hail with YYR having freezing levels below 8000 ft.

 

For the Maritimes things are trickier. Cloudiness will be the key. There’s some upper support from a 500 mb jet near southwestern New Brunswick with some associated lift, with plenty of moisture below 700 mb. PWATs range from 40-60 mm, with surface dewpoints near 20 C,  and 850 dewpoints up to 15 C , with a moist tongue poking into southern New Brunswick. If things clear, CAPEs of up to 1000 J/kg or maybe higher are possible. Freezing levels near 15,0000 ft suggest large hail is unlikely. Very heavy rainfall is the largest risk, followed by gusty winds that may reach warning level, and finally some small hail. For the rest of New Brunswick and parts of Nova Scotia, the impacts will be somewhat weaker, but rainfall followed by winds as the main risks.

 

 

Thunderstorm Outlook for Day 2

 

Convective Outlook Valid for Today and Tomorrow

Thunderstorm Outlook for Day 1

 

Regional Impacts

New Brunswick: Possibility of non-severe thundershowers in the northeast if the thick cloud there burns off this afternoon. Possibility of Severe thundertorms in the extreme southwest if the cloud deck moves away or burns off,  with high wind the largest risk, followed by heavy downpours.  

Newfoundland: thunderstorms beginning this afternoon with possible heavy downpours, especially with the slow movement of the cells.

 

Convective Discussion

 

For Newfoundland: there’s a low of the coast of Labrador  from 250 mb down, with some upper dynamic support with PVA approaching western Newfoundland.  There’s some good moisture with dewpoints of up to 17 C and PWATs near 24 mm, with most of it below 850 mb, Shear and storm motion is relatively low,  suggesting plenty of time for rain to accumulate, and mean layer CAPEs suggest possibly reaching or exceeding 500 J/kg near and west of Gander, if they can get some clearing. Small hail is also possible, with freezing levels around 10-11,000 ft.

 

For New Brunswick:  there are some good ingredients, especially in the far southwest, but the big inhibitor is cloudiness.  The most likely place for convection is in the northeast, where things may start clearing this afternoon, but with non-severe cells likely. The general ingredients are near 50 kts of shear, PWATs in the 30-45 mm range, with surface dewpoints near 19 C and 850 dewpoints near 13 C moving in from the west.  If things clear in the north, CAPEs could reach 200-500 J/kg.  Gusty winds and local heavy downpours are the main threats, but the cells should move fast enough to limit therainfall from any given cell.

 

For the southwest the main risk would be wind gusts possibly reaching warning level, followed by local heavy downpours. Again, this is assuming some surface insolation this afternoon.

 

 

Thunderstorm Outlook for Day 2

 

Convective Outlook Valid for Today and Tomorrow

Regional Impacts

Maritimes – Heavy rainfall with small hail and strong gusts with the strongest likelihood along coastal NS but eastern inland NS and eastern NB also possible.

Newfoundland and Labrador – risk of thundershowers with slight chance of severe over central and northeast.

 

Convective Discussion

Potential for thunderstorms today for some regions.  Upper dynamics will become favourable for tstorm formation today as the Maritimes enters the left exit area of an upper jet and area of diffluence.   Cooling aloft through the first part of the day will help destabilize the upper atmosphere.  Closer to the surface, there is quite a bit of moisture at the surface but it does not extend significantly up to 850mb.  There is some higher moisture values moving in today but again…not significantly high.  Precipitable water values of around 25 to 30 mm are expected.  0-6 km shear values as high as 35 kts so this will be enough to maintain tstorms if/when they form.  500 to 1000 J/kg of CAPE can be expected today for the Maritimes.  The one thing that seems to be lacking is a significant synoptic feature to kickstart tstorms.  What we will have is coastal convergence along sea breeze fronts that are expected to develop this afternoon.  That will be the main area of concern but inland areas could get tstorms if there are some weak areas of convergeance in the area or if coastal storms advect.  The highest impact would be heavy rainfall as storms along the coast will likely be moving slowly and/or training could develop. Newfoundland is farther from the favourable dynamics today but still have a risk of thunderstorms especially over central and northeast.

 

Thunderstorm Outlook for Day 1

 

Thunderstorm Outlook for Day 2

 

Barrie MacKinnon

 

Convective Outlook Valid for Today and Tomorrow

Regional Impacts

Southeastern Labrador could experience strong thunderstorms this afternoon - the main threat is damaging wind gust, brief downpours and small hail – into the evening.

 

Convective Discussion

This morning, a frontal wave was located south of Newfoundland. The elongated front has an history of producing locally heavy rain as far back as NB (reports of rainfall rates of 20-40 mm). Earlier lightning activity has faded during the past two hours. This feature will continue to move eastward – out of the region - throughout the afternoon.

The main are of focus for the afternoon is Labrador where an upper cold low prevails. The cold pool would be sufficient to trigger isolated thunderstorms, but this likelihood will be enhanced by an approaching vorticity rotating around the low. The moisture available in this airmass is not tremendous, but the energy available is high enough to anticipated the development of fairly robust eastward moving storms capable of producing small hail, damaging wind gusts and localised downpours.

 

 

Thunderstorm Outlook for Day 1

 

 

 

Thunderstorm Outlook for Day 2

 

 

Convective Outlook Valid for Today and Tomorrow

Regional Impacts

Strong clusters of thunderstorms could produce localized heavy downpours early this afternoon over southwestern Nova Scotia.

Later this afternoon, thunderstorms formation over central and southern Maine could spread robust clusters over southwestern New Brunswick, the main threat would be brief heavy rain and damaging wind gusts.

 

Convective Discussion

 

An upper trough along with a weak cyclonic upper jet over northern Quebec could trigger an isolated thunderstorm over western Lab, in the east Goose is showing stability in the mid-levels so convection will be limited to fair weather cumulus. For the Maritimes, two distinct air mass present different threat. For Nova Scotia a surface front extends from the New England coast to Northumberland Strait, a southwesterly low-level jet is feeding moisture over the area with moderate to heavy rain expected at times. For New Brunswick, a surface feature to the west will provide the forcing necessary for thunderstorm initiation over the Maine Highlands. A 100kt upper level jet could help sustain these individual storms long enough for them to propagate eastward into western NB.  Although the main threat with these storms would be brief downpours and damaging wind gusts - none of the severity indicators are particularly high at this point.

 

Thunderstorm Outlook for Day 1

 

 

 

Thunderstorm Outlook for Day 2

 

Convective Outlook Valid for Today and Tomorrow

Regional Impacts

 

NS/NB/PEI: None

Nfld & Labrador:  A risk for offshore waters.

 

Convective Discussion

 

A weakening cold front is moving across Newfoundland today.  There is a very small chance of thundershowers this afternoon over eastern Newfoundland but should be confined to offshore waters.  

 

 

Thunderstorm Outlook for Day 1

 

 

 

Thunderstorm Outlook for Day 2

 

Convective Outlook Valid for Today and Tomorrow

Regional Impacts

 

New Brunswick: Severe thunderstorms possible giving local heavy downpours, strong wind gusts, and small hail this afternoon in central and southern New Brunswick.

 

Labrador: Locally heavy downpours, moderate to strong wind gusts, and hail are possible today and this evening over central and western Labrador.

 

Newfoundland: Isolated embedded thunderstorms giving locally heavy downpours and moderate winds gusts are possible today over western Newfoundland and surrounding marine waters.

 

 

Convective Discussion

 

There are a few areas of interest to keep an eye on today. A strong area of low pressure currently over northern Quebec will move over northern Labrador this evening. Meanwhile, a short wave with a warm front has been moving over the Gulf of St. Lawrence this morning and into western Newfoundland, firing off some embedded thundershowers this morning which may continue into the early afternoon and possibly into the overnight period. Thirdly, the cold front currently over southern Quebec will track through New Brunswick this afternoon and into Newfoundland overnight.   

 

The highest areas of concern are over central/southern New Brunswick and Labrador this afternoon. The upper dynamics are favourable over Labrador as they are within the left exit of an upper jet with ample diffluence and cooling aloft at 500 mb. Precipitable water values are in the high 20s. The main thing holding any cells the develop is the lack of strong wind shear.  There could still be enough energy that some cells could form strong lines with moderate to strong wind gusts and small hail given freezing levels near 12,000 ft.

 

For New Brunswick, there is the potential for severe thunderstorms with some favourable upper dynamics and the cold front being the trigger ahead and along it this afternoon for central and southern areas. There is ample moisture with precipitable water near 50 mm, and 0-6km shear in the low 40s but shear will be decreasing into the afternoon.  The main inhibitor is a current capping inversion seen on the 12Z Caribou sounding at 750mb and some additional warming between 500-700mb. Therefore, daytime heating and any additional low-level moisture will be the key in if this area sees only 500 J/kg CAPE values, or over 1000 J/kg. There is enough clearing over northwestern New Brunswick that cloud cover does not look to be an issue. Should this cap break, some stronger squall lines could develop with heavy rain (25+mm/h) and strong winds ( 70-90 km/h) as well as a slight possibility of supercells ahead of the front. Small hail (<2 cm) is also possible but freezing levels near 15,000ft should prevent any large hail from developing.

 

Thunderstorm Outlook for Day 1

 

 

 

Thunderstorm Outlook for Day 2

 

Convective Outlook Valid for Today and Tomorrow

Thunderstorm Outlook for Day 1

 

Regional Impacts

New Brunswick: Scattered thundershowers beginning by early to mid afternoon, with some heavy downpours and gusty winds.

Labrador: Isolated to scattered thundershowers with some gusty winds and brief heavy showers.

 

 

Convective Discussion

 

There’s a deep upper low over northern Hudson Bay , with a deep upper trough extending southeast over western Labrador into the eastern Gulf of St. Lawrence. There is also a deep upper thermal trough west of Labrador. Weak to moderate 250 and 500 jets have Right Exits near and north of the Gaspe Peninsula and all of this is slowly moving east. There is a reasonable chance for near severe thunderstorms for New Brunswick, with a slight chance for severe. Upper dynamic support is limited to the extreme north of the province, but there is healthy shear near 40 kts, moderate PWAT around 30-35 mm,  but with no really significant amounts from the surface to 700 mb, then with some drying. The main mechanism will be daytime heating, and some extra moisture from low stratus over New Brunswick, and a surface trough from western Labrador to just northwest of New Brunswick along the St. Lawrence as a possible organising feature. The main impacts will be locally heavy downpours and some gusty winds. Significant hail is unlikely, with freezing levels near 115 to 145 hft for Caribou and Gray.

 

For Labrador TCus have started, associated with the trough over western Labrador, and some thundershowers should start soon. This and daytime heating are the triggers and organising features. PWAT is 15 mm near YYR and 30 near YWK,  And shear is near 15 kts east and 25 west. The stability will inhibit things somewhat with a weak inversion from near 800 mb upwards. All this suggests the western cells will be a bit more  intense. Maximum CAPEs should be near 250 J/kg. So the major impacts are some intense but brief showers, some gusty winds, and a slight chance for hail.

 

 

 

Thunderstorm Outlook for Day 2

For day two a deep upper ridge starts to move in, and upper  dynamic support is minimal. However weak low level troughs approach western Labrador and the western Maritimes, and there’s a chance for some thundershowers, with a bit more support for New Brunswick with higher moisture, shear, and potential moderate CAPE.

Convective Outlook Valid for Today and Tomorrow

Regional Impacts

 

Southern Grand Banks may see some elevated thundershowers today and overnight. No other regional impacts are expected.

 

Convective Discussion

 

An upper-level low is slowly tracking over the southern marine district and will stall over the Grand Banks today and tomorrow. Most convection associated with the low is now south of the Maritimes marine waters, however, a strong southerly push over the eastern Grand Banks and upper level jet over the area will help lift. The highest risk for embedded convection will be in the overnight hours into Friday morning, when cloud top cooling will also help to enhance the destabilisation aloft.

 

Thunderstorm Outlook for Day 1

 

 

 

Thunderstorm Outlook for Day 2

 

A large trough will approach Atlantic Canada from central/northern Quebec on Friday and a secondary trough further south over southern Quebec. At this time, the dynamics appear more favourable further west over Quebec as the air aloft over New Brunswick remains too warm and would need a good amount of surface based heating in order to break the cap. Showers are expected to move into western New Brunswick in the mid afternoon so cloudiness out ahead in the morning could be key factor for anything getting going other than showers. Low risk has been added for now.

 

 

Convective Outlook Valid for Today and Tomorrow

Regional Impacts

 

Eastern Nova Scotia, southeastern Newfoundland, and the southern marine district will see locally high rainfall amounts with embedded thunderstorms possible mainly over the southern marine waters as an upper level features slowly moves eastward south of Nova Scotia today.

 

Convective Discussion

 

An upper-level low south of Nova Scotia will move eastward toward the Grand Banks today and stall over the area into Friday. For today, the primary threats for embedded convection will remain offshore near and ahead of the low centre, but there could be some enhancement this afternoon over eastern parts of Nova Scotia including Cape Breton as the low drifts further east. This system had a history of dropping high rainfall amounts over parts of southwestern Nova Scotia with precipitable water values of near 40 mm were and this may be the case today over eastern portions.

 

Thunderstorm Outlook for Day 1

 

 

Thunderstorm Outlook for Day 2

 

The upper-level low will stall over the southeastern Grand Banks where some embedded convection may develop in the overnight hours into Friday morning.

 

Convective Outlook Valid for Today and Tomorrow

Regional Impacts

 

Nova Scotia.. A stationary area of thunderstorm development over southwest Nova Scotia could produce locally heavy rainfall amounts of 20 to 30mm.

 

New Brunswick.. A low probability of isolated thundershowers late this afternoon or this evening.

 

Convective Discussion

 

Thunderstorm development is expected to continue ahead of and near an upper low that is slowly progressing towards the Maritimes. Most of the convection will be triggered aloft but daytime heating could contribute to increased updraft strength this afternoon. There is some indication that a quasi-stationary feature could set up possible giving heavy rainfall amounts to some parts of southwest Nova Scotia.

 

Thunderstorm Outlook for Day 1

 

 

Thunderstorm Outlook for Day 2

 

Convective Outlook Valid for Today and Tomorrow

Regional Impacts

 

Isolated Thunderstorms could develop over New Brunswick. No Severe weather expected.

 

Convective Discussion

 

There is a slight potential for thunderstorms to develop over New Brunswick today. Overall cape values are low at less than generally 500 j/kg but with high dew point temperatures. The approaching trough moving from the north may provide a sufficient trigger for storms to initiate. However with weaker updrafts severe storms are unlikely.

 

Thunderstorm Outlook for Day 1

 

 

Thunderstorm Outlook for Day 2

 

Convective Outlook Valid for Today and Tomorrow

Regional Impacts

For New Brunswick.. Heavy Downpours and winds gusting to 70km/hr are possible in thunderstorms.

 

For Labrador.. In addition to the heavy rain, downpours in thunderstorms and gusts to 50 km/hr are possible in thunderstorms.

 

Convective Discussion

The amount of available moisture available today is very high with precipitable water values between 40 and 50mm for most of the region. The main synoptic feature is the trough of low pressure that is moving through Labrador and eastern Quebec today. The trough should be sufficient to trigger some thunderstorms over Labrador but updrafts should remain weak enough that severe thunderstorms are unlikely, however there is still a slight possibility of severe storms and the situation should be monitored. Over New Brunswick slightly stronger updrafts will increase the potential for severe thunderstorms with mean layer capes between 1000 – 1500 j/kg. Thunderstorms are likely to move into the area this afternoon, and with low level shear values exceeding 30 knots there is some potential for organized convection. Watches may be required.

 

Thunderstorm Outlook for Day 1

 

 

Thunderstorm Outlook for Day 2

 

Convective Outlook Valid for Today and Tomorrow

Regional Impacts

Thunderstorms likely in western Labrador giving heavy downpours of rain and possible small hail. Gusty winds up to 40 knots are possible.

Non-severe thundershowers possible in western New Brunswick.

 

Convective Discussion

There is lots of low-level heat and moisture to give energy for convection in Atlantic Canada. However, cloud cover and low CAPEs are limiting factors in the Maritimes.

 

The best chance for significant convection today is in western Labrador. There is upper level dynamics with a 50-60 knot jet at the 250 level. The 0-6 km shear if about 40 knots. If there is sufficient sunshine as a trigger, the CAPE is between 1000 and 1500 J/kg in the extreme west and about 500 J/kg east of Churchill Falls.

 

Thunderstorm Outlook for Day 1

 

 

Thunderstorm Outlook for Day 2

 

Convective Outlook Valid for Today and Tomorrow

Regional Impacts

Western Labrador: risk of afternoon and evening thundershowers.

Northern New Brunswick: Risk of afternoon and evening thundershowers.

 

Convective Discussion

Isolated thundershowers are expected to form over western Labrador this afternoon in association with a trough of low pressure moving into the region from Quebec. La Grande tephi shows decent shear but somewhat of a cap in the mid-upper levels. PWAT is around 36 mm. Expected non-severe cells to develop with locally heavy rainfall and gusty winds.

 

There is also the risk of a thundershower this afternoon and evening across northern New Brunswick. KCAR tephi shows 500+ CAPE but very little shear. There is also the lack of a trigger so if cells do develop they will be slow moving. PWAT is around 35 mm so heavy downpours would be the main concern. Looking at both the YQI and YAW soundings it will be quite difficult to generate CBs in NS. However local areas of convergence could generate an isolated cell.

 

Thunderstorm Outlook for Day 1

 

Thunderstorm Outlook for Day 2

Convective Outlook Valid for Today and Tomorrow

Thunderstorm Outlook for Day 1

 

Regional Impacts

New Brunswick and Prince Edward Island: Slow moving non-severe thunderstorms developing this afternoon, with local heavy downpours and gusty winds. Near the Bay of Chaleur a slight chance for severe wind gusts, and a possibility of 2 cm hail this afternoon.

Labrador: continuing non-severe thunderstorms, tapering off this evening, with local heavy downpours and gusty winds.

 

Convective Discussion

A deep upper low over the northern Labrador Sea has two associated troughs, on extending from the low southwest to southwest of  Labrador, with some associated PVA. And a second roughly north-south trough over the eastern Gulf of St. Lawrence, again with some PVA. For the second trough there is a deep inversion, inhibiting significant convection for Newfoundland.  For Labrador the profiles are good for CAPE maxing between 500-1000 J/kg this afternoon, and reasonable PWAT possibly exceeding 25 mm, but with shear on the low side around 15-25 kts. While freezing levels are near 9500 ft at Goose Bay, the low shear argues against a separation of updraft and downdraft, possibly inhibiting hail growth. The main impacts should be heavy downpours and some brief strong gusty winds.

 

For most of New Brunswick there will be airmass convection, with decent moisture (PWAT near 30 mm and surface dewpoints in the 17-20 C range and some low level strauts burning off), good insolation after the cloud clears, shear in the 25-35 kt range, and surface based CAPEs possibly nearing 1000 J/kg this afternoon. Freezing levels in the south are too high for hail at about 15,000 ft, but in the north they are about 11,500 ft, which given the CAPE and the shear, gives a possibility for hail. In the Bay of Chaleur a weak jet and PVA may enhance conditions enough for near severe gusty winds, and a slight chance for 2 cm hail.

 

 

 

Thunderstorm Outlook for Day 2

 

 

 

Convective Outlook Valid for Today and Tomorrow

Regional Impacts

New Brunswick: mainly non-severe thundershowers this afternoon into this evening for most of the province. In the northwest marginal severe thundershowers with the highest threat for gusty winds and local heavy downpours.

Nova Scotia: non-severe thundershowers this into this evening and overnight for most of the province.

Labrador: non-severe thundershowers this afternoon into this evening, with a second batch possible overnight.

 

 

Convective Discussion

 

There is currently a deep upper ridge east of Labrador with a trough just west of it over Labrador. This will move east this afternoon into this evening, just west of the trough there will be a jet approaching  with the left exit region over northwestern New Brunswick by this evening. Finally there is a surface frontal  trough moving in from the northwest this afternoon and then moving across Nova Scotia tonight.  There’s also weak destabilisation aloft between a thermal ridge over Labrador and a weak thermal trough east of James Bay. We have some good insolation this afternoon and ample low level moisture, with 850 dew points 12-14 C, surface dew points in the 16-20 C range and PWAT in the 30-40+ mm range being maintained by a southwesterly flow. The shear is fairly low, around 20-25 kts currently.  

 

So mainly multi-cells getting organised eventually along the approaching frontal trough, some heavy downpours with gusty winds likely, and a low chance of hail with freezing levels in the 12,000 ft range. The chance for severe wind gusts may be enhance if a squall line or derecho forms this evening. The trough will also probably keep convection going well into the evening.

 

Thunderstorm outlook for day 1

 

 

 

 

Thunderstorm Outlook for Day 2

 

 

 

Convective Outlook Valid for Today and Tomorrow

Regional Impacts

 

Isolated non-severe thunderstorms may develop over eastern parts of Labrador.

 

Convective Discussion

 

For the most part today looks fairly quiet as an upper ridge progresses slowly eastward towards the region today. This building ridge will suppress most deep convection today with most of the thunderstorm activity remaining over Ontario and Quebec. A weak surface tough along with most unstable cape values 500-1000 j/kg could be sufficient to trigger some isolated thunderstorms over eastern Labrador this afternoon however no severe storms are expected.

 

For tomorrow we will begin to see the breakdown of the upper ridge, this along with increasing low level moisture could help trigger thunderstorms over western New Brunswick and western Labrador tomorrow afternoon.

 

Thunderstorm Outlook for Day 1

 

 

Thunderstorm Outlook for Day 2

 

Convective Outlook Valid for Today and Tomorrow

Regional Impacts

Isolated non-severe thunderstorms over central and eastern NB to the Bay of Fundy, Annapolis Valley and northwestern NS, also southeastern Labrador.

 

Convective Discussion

This morning an upper trough extends over the Gulf of St. Lawrence and eastern portions of the Maritimes, with extensive cloud&rain detected on Sat and Rad. A northerly jet streak and some other upper support will maintain unstable conditions and trigger the development of isolated thunderstorms just behind the trough. Further to the west, conditions will generally begin to dry out as a ridge continues to build over Ontario and western Quebec – this is a prelude to the arrival of the next warm airmass.

Another area for potential thunderstorm development is over southeastern Labrador where a surface trough currently over the mid coast will continue to progress southward. Sat imagery is already indicating the presence of glaciated towering cloud tops over the mountains east of Goose Bay. These storms may become somewhat organised (along the trough) and present the appearance of a solid line. Winds may gust between 50 to 70 km/h ahead of these storms.

 

 

Thunderstorm Outlook for Day 1

 

Thunderstorm Outlook for Day 2

Convective Outlook Valid for Today and Tomorrow

Regional Impacts

Isolated non-severe thunderstorms over New Brunswick and Southern Labrador. Stronger storms will likely occur over Maine, and could move close to western New Brunswick.

 

Convective Discussion

There are a couple of upper features this morning supporting convective development throughout the day.  An upper low just west of Labrador with its associated cold pool will maintain unstable conditions over areas from Wabush to Churchill Falls and Goose Bay. Spotty lightning has been detected throughout the morning especially in the area between Wabush and Sept-Isle, and also between Smallwood reservoir and Goose Bay. MLCAPE in the order of 300 to 500 J/kg will support development of individual cells capable to produce brief downpours - small hail - and gusts of around 60 km/h.  

A thermal trough extends southward from the cold pool to Maine and then to Long Island. Two jet branches will intersect with the trough, one of those is oriented west to east along the lower Quebec North Shore, and the second branch is pushing southward over the St. Lawrence Valley moving into Maine where the most unstable upper air profiles were found this morning. Gray, Maine shows MLCAPE values of around 1000 J/kg and lifted index of -2 to -4. This is an area were multi- cell development is likely during the afternoon due to the incoming northwesterly jet intersecting with the trough, providing extra support to these storms sustained by deep-layer shear values of about 30 knots. While the bulkier action will remain west of New Brunswick, weaker non-severe storms will likely develop over the province.

 

Thunderstorm Outlook for Day 1

 

 

Thunderstorm Outlook for Day 2

Convective Outlook Valid for Today and Tomorrow

Regional Impacts

 

A risk of thundershowers for western Labrador today. Thundershowers have already popped up northeast of Sept-Iles.

 

Convective Discussion

 

Marginal cape values of 400-500 J/kg and shear of 20-30 kts are expected for western Labrador today. Supportive upper flow and vorticity will yield a risk of thundershowers with some daytime heating this afternoon/evening.

 

 

Thunderstorm Outlook for Day 1

 

 

 

Thunderstorm Outlook for Day 2