Convective Outlook Valid for July 31st, 2019

Convective Discussion

 

This could be a very active day for much of the Atlantic Provinces with the main focus of energy being over New Brunswick and possibly spreading into western PEI. In general there will be a weak surface trough from western Labrador then through New Brunswick which will help aid in the thunderstorm initiation. For most of the Maritimes there are high CAPE values between 1000-2000 J/kg and very high levels of moisture, this will lead to a high probability that heavy down pours will occur. Over Newfoundland and Labrador updrafts will be much weaker however with the high moisture content of the airmass locally heavy rain is still a possibility. Over New Brunswick the wind shear is sufficient to organize some storms, longer lived thunderstorms can be expected with a low chance of supercell and bow echo formation. Should stronger storms develop strong wind gusts 70-90 km/h and hail of 2-4 cm is possible.

 

Over Nova Scotia dynamics are not as favorable however there is a chance that back building thunderstorms could develop along the spine of nova scotia.

 

Regional Impacts

 

New Brunswick… Heavy Rain 25-50mm in heaviest thunderstorms, Hail 2-4 cm and wind gusts 70-90km/hr.

 

Nova Scotia… Heavy Rain 25 mm, locally higher amounts in back building thunderstorms.

 

PEI… Heavy Rain 25-50mm in heaviest thunderstorms, Hail 2-4 cm and wind gusts 70-90 km/hr over western areas possible.

 

Newfoundland and Labrador… Locally heavy downpours 20mm, small hail possible over western Labrador.

 

 

 

 

Convective Outlook Valid for July 30th 2019

Convective Discussion

 

An upper ridge moving over the Maritimes will suppress the convection somewhat and may inhibit convective initiation till late in the day. Overall the CAPE values are quite favorable being greater than 1000 j/kg for most of the Region. 0 – 6 km Wind shear values are of 35-40 knots over NW NB and for Newfoundland this will increase the potential for organized convection over these areas. Over Newfoundland if convection occurs it will likely begin early this afternoon while the thermodynamics still remain strong. Over New Brunswick the probability of severe weather is low but it is possible that severe thunderstorms could advect from Maine late in the day.

 

Regional Impacts

 

New Brunswick…

A general risk of thunderstorms for most areas with a heightened risk of severe storms for northwest areas, local rain of 25mm. If severe thunderstorms develop they will be very late in the day as dynamics gradually become more favorable.

Nova Scotia…

A low risk of thunderstorms that could produce local rainfall amounts near 20mm. A slight risk of that multiple thunderstorms could move over the same area causing further amounts.  

 

Prince Edward Island…

A low risk of thunderstorms that could produce local rainfall amounts near 20mm.

 

Newfoundland…

A low risk of thunderstorms that could produce local rainfall amounts near 25mm and wind gusts of 50-70 km/hr. A slight risk of that multiple thunderstorms could move over the same area causing further amounts.  

 

Labrador…

There is a chance of thunderstorms embedded in the trough that is approaching from Quebec.

 

 

Mel Lemmon

 

 

 

 

Day 1 Convective Outlook for Atlantic Canada Valid for July 29th, 2019

Convective Discussion:


Convective activity expected today over much of the Atlantic Canada with small chance of some convection becoming severe.

Lots of low level moisture and solar insolation will kick off some thundershowers across much of the Maritimes today. Shear is around the 25 – 35 kt mark and there are no substantial synoptic features to kick start and/or organize things. There is also a mid level warm nose which should cap off some but not all convective activity. So generally speaking, thundershowers over the Maritimes should be non severe but over area with shear near 35 kts, there is a chance of longer lived thundershowers that could become organized and become severe. There is also a possibility of tstorm formation over or along the Annapolis valley that could become quasi-stationary and extend out towards Antigonish county. The main threat if severe thunderstorms develop is heavy rainfall but hail and winds near criteria are also possible.

An area of low pressure over Labrador and an associated trough will kick off mid level tstorms over the area. Generally speaking, these thundershowers are expected to be non severe but a line currently over then Northeast Gulf could bring down some heavy downpours over parts of western Newfoundland.

Regional Impacts:
Maritimes: Slight chance of heavy rainfall reaching 25mm/hr.

Newfoundland: Slight chance of heavy rainfall reaching 25mm/hr over parts of western Newfoundland.

Labrador: Severe thunderstorms not expected.

Marine areas: Heavy rainfall over northeast gulf. Winds possibly reaching ~35 kts in thunderstorms.

Barrie MacKinnon

Convective Outlook Valid for July 26 2019

Convective Discussion:


Thunderstorms are unlikely over Atlantic Canada today due to very dry conditions and subsidence in the mid levels over the Maritimes and Newfoundland. The subsidence inversion in the 700 to 600 mb layer should suppress any convection exceeding that layer. These conditions are the result of a large surface high over southern areas and an approaching upper level ridge today and tonight. Showers are likely later today over southeastern and central Newfoundland. However, the dry air and subsidence aloft should prevent any TCu’s that form from obtaining sufficient height to become CB’s.


Over Labrador, relatively warm air aloft and cool air in the low levels will give a profile too stable for deep convection. In addition, mid-level cloud and moisture will suppress solar insolation.


Regional Impacts:

Maritimes: none.

Newfoundland: Scattered showers, thundershowers unlikely.

Labrador: none.

Marine areas: none. 

Convective Outlook Valid for July 25 2019r

Convective Discussion:

A slight chance of thundershowers over northern Labrador and for the southern border between Labrador and the Quebec border. Over southernmost sections of the Scotian Shelf and the southern Grand Banks occasional thundershowers.

Today a broad trough will be moving into Labrador from the west as a trigger, with some associated cooling aloft and weak destabilisation. The main inhibitor is again a lack of moisture. From 850 mb and higher there is precious little moisture, and at the surface the dew points are near 10 C or less.  PWATs over and upstream of Labrador are only near 17 mm. Now there is some low to mid level cloud moving in , which may supply the necessary moisture. Topographic forcing may help a little north and south, as previously mentioned. Impacts will be mainly some gusty winds , followed by  some brief heavy showers,  Freezing levels are again below 9000 ft, so there is a slight chance for small hail.

For the Maritimes there is little upper forcing, low shear near 20-25 kts, PWAT less than 20 mm, and low to moderate dew points. For Newfoundland the shear is higher as is the PWAT in the southeast, but upper forcing  is again limited. Finally , Stephenville and St. John’s tephis, show a moderate cap in the west and a strong cap in the east.

For offshore waters, high SSTs near the North Wall of the Gulf Stream will trigger some thunderstorms, further north isolated embedded convection is possible,

Regional Impacts:

Maritimes and Newfoundland: none.

Labrador: low chance for non-severe convection for northern Labrador and the southern border.

Marine areas: occasional non-severe thunderstorms over the southern Scotian Shelf, as well as the southern Grand Banks.

Doug Mercer

Convective Outlook Valid for July 24 2019

Convective discussion:

Non-severe thunderstorms possible for Labrador, western New Brunswick, and most southern offshore waters. Severe is likely near Geroges Bank, where squall warnings are in effect.

Currently there is a trough extending over southwestern forecast waters, which currently have SSTs above 26 C.  This is giving CAPEs near 2500-3000 J/kg, and wind gusts in excess of 40 kts are likely. PWAT is in the 50 mm range. But 0-6 km Shear is low, near 20 kts. So these are multicells organised along the weak trough moving though. While SST’s drop gradually farther east, there are still SSTs near 20 C  for  southernmost parts of Laurentian Fan and the Grand Banks

For western New Brunswick the main limiting factor is moisture. PWAT is near 20 mm, at 850  mb dew points are near or less than 8 C, and surface dew points are less than 16 C. While there is a strong  upper jet over the province, it is not well placed for any significant lift. There is a weak trough over the southern part of the province, and some low level moisture is advecting in from southern Maine. Conditions are clear with come Cu setting up. Based on this there is a chance for isolated thundershowers this afternoon and ending this evening, with the highest chance in the south.

For Labrador there is a QS low near Ungava bay with a trough extending south crossing western areas moving towards the coast, giving weak lift enhanced a bit near the trough. A slowly approaching deep thermal trough from the west will help destabilise things,  and the aforementioned upper jet is over southernmost Labrador. The left exist is a bit too far east, but may enhance things along the border range in the south, and maybe south of Lake Melville near the coast. Limiting factors are again low PWAT amounts near 20 mm, and  low dew points. Excpect non severe thundershowers with some moderate wind gusts. With freezing levels generally below 8500 feet, small hail is possible.

Regional Impacts:

Labrador: non-severe thundershowers are expected this afternoon into this evening. These’s a chance of near severe cells near the southern border of Labrador.

Western New Brunswick: slight chance of thundershowers this afternoon.

Slope waters  extending to south of the Avalon Peninsula: For western slope waters just south of the main discussion area, squalls are likely for western areas. Elsewhere non-severe embedded thundershowers are expected.

Doug Mercer

Convective Outlook Valid for July 23, 2019

Convective Discussion.

 

There is a slight risk of TSRA across CNTRL LAB today in conjunction with an approaching upper area of low pressure, and associated troughing in the middle and upper-levels. The closest TEP to try and analyze was YVZ, but it’s likely too far downstream. However adjusting for a surface temperature of 24 and adding a little moisture in the low levels could produce and few hundred joules of CAPE. Very little in the way of shear so I would expect just some ISOL pulse cells. SAT pix is showing some clearing skies so would expect convection to initiate once the Tc has been reached…early to mid afternoon.

 

A nearly stationary trough of low pressure south of NS and NL will continue to produce some SCT TS through today and tonight. The TEP out of KCHH has a 50+ LLJ at 850 mb, which is a little discerning. It wouldn’t take much to mix that wind to the surface. The afternoon marine forecast for waters south of NS will included PSBL wind gusts near thunderstorms. The SE Avalon may get clipped with some embedded TSRA tonight (say from St. Shott’s up through Cappahayden)…but it’s a marginal risk at best. PW is in the order of 40 to 50 (from the YQI TEP) so areas where there are no TS could see very heavy rains today and tonight (NS and SE NL). OTZ quiet weather for the rest of the region.

 

Regional Impact.

 

CNTRL LAB: risk for non-severe TS this afternoon.

 

NS and SE NL: LCL HVY RA today and tonight…with slight risk of TSRA for the SE Avalon tonight.

 

Elsewhere: nil sig wx.

 

 

Jeremy

Convective Outlook Valid for July 22, 2019

Convective Discussion.

 

Not a whole lot on the go today after a day of storms across NS yesterday. There is a fairly stationary trough/cold front sitting south of NS that will produce the occasional TS through the course of the day. 12Z surface analysis shows a weak waves along the front SE of the Great Lakes. Guidance moves that feature towards SW NS later tonight…so there could be some ISOL elevated TSRA after midnight.

 

The feature worth mentioning is an area of vorticity (observed on WV imagery) currently to the NE of Anticosti Island. This lobe is moving generally eastward and could produce some ISOL convection today. This area is also in the vicinity of the left exit region of a strong 250 mb jet.

 

Regional Impacts.

 

Newfoundland: PSBL ISOL TSRA in association with the area of PVA at 500 mb.

 

Nova Scotia: ISOL elevated TSRA PSBL after midnight tonight down across portions of SW NS.

 

Elsewhere: NIL SIG WX.

 

 

Jeremy

Convective Outlook Valid for July 21, 2019

Convective Discussion

 

The focus for severe weather today will be regions adjacent to southeastern Maine, and also inland portions of western Nova Scotia where hot and humid conditions prevail. Strong thunderstorms have migrated from Quebec over Maine this morning and are now entering Charlotte county in southwestern NB. These clusters of thunderstorms have a history of producing hail the size of a ping pong ball. The latest radar presentation suggests that these clusters are becoming better organized and are beginning to look more like early stages of squall lines. One of these features extends from Oromocto Lake to St. Stephen, and another one stretches NE-SW upstream from Bangor.

 

Convection should initiate during the first half of the afternoon over inland areas of Nova Scotia. The best forcing is expected over western regions but any storms that form could migrate to other regions of the province during the later part of the day. Buoyancy will increase throughout the afternoon and some of the forcing mechanisms will become better aligned. Using a Ts of 34 and Td of 24 is enough generate CAPE values in excess of 1500 J/kg pushing the lifted index to -5 or less. These large cumulonimbus would then become long-lived in this moisture-rich environment where deep layer shear of 30-40 knots are expected.

 

Regional Impacts

 

New Brunswick…For southernmost regions, strong thunderstorms with clusters of frequent lightning, widespread downpours, hail and locally severe winds.

 

Nova Scotia…For western regions, strong thunderstorms with clusters of frequent lightning, widespread downpours, hail and locally severe winds.

 

Newfoundland and Labrador…Isolated non-severe thunderstorms over southeastern regions.

 

PEI…None

 

 

Convective Outlook Valid for Month Day Year

Convective Discussion

 

A strong upper level jet stream (150 knots) runs from the Southern Prairies-Northern Ontario-Central Quebec-and then drops southeastward over the Gulf of St. Lawrence and then south of Newfoundland. Cloudy and cool conditions prevail in the airmass northeast of this feature, while hot and humid conditions prevail southwest of it.

This mornings upper-air soundings from CAR GYX and YQI are showing strong capping around 600mb, and a definite lack of forcing mechanism in the upper levels. The hot humid conditions will not be enough to trigger surface-based convection this afternoon. For this evening and overnight, some airmass thunderstorm activity from the lower Great Lakes and Northern New England may reach Maine and spread into western NB.

Regional Impacts

 

New Brunswick…Risk of a thunderstorm with localized downpours this evening and overnight

 

PEI and Nova Scotia…None

 

Newfoundland and Labrador…None

 

 

Convective Outlook Valid for July 19th, 2019

Convective Discussion

 

A short wave trough is approaching New Brunswick from central Quebec today. An increasingly more hot and humid air mass is also approaching the region this afternoon over western New Brunswick as winds begin to shift to the southwest on the  backside of a ridge of high pressure. This trough is expected to bring showers and thundershowers to northern New Brunswick this afternoon and continue to track eastward towards Nova Scotia and western Labrador by tomorrow morning.

 

The air mass will become increasingly warmer in the low levels which will lead to further instability this afternoon. As the trough approaches northwestern New Brunswick, 0-6km wind shear will increase somewhat but remain moderate, with divergence aloft and the approach of a strong 250mb jet to help maintain convection. Only modest CAPE values of 200-500 J/kg are expected, except perhaps for extreme northwestern New Brunswick which could exceed 500 J/kg. It is expected that multicellular storms will be the dominant type of convection with brief heavy downpours and strong wind gusts possible with some cells possibly developing stronger lines of convection over northwestern New Brunswick this evening. Freezing levels remain high enough that hail is not expected to be a main threat with cells that develop today.

 

Regional Impacts

 

New Brunswick…Lightning, locally heavy rainfall amounts, and brief strong wind gusts are possible for northern and central New Brunswick this afternoon and evening.

 

PEI and Nova Scotia…Scattered showers with the slight risk of a thundershower maintaining into the late evening possible.

 

Newfoundland and Labrador…None

 

 

Roberta McArthur

 

 

Convective Outlook Valid for July 18th, 2019

Convective Discussion

 

We are in for a mainly quiet day convective wise for Atlantic Canada. Two upper level lows had continued to trigger some non-severe elevated convection this morning over Funk Island Bank and the northwestern Labrador Sea. These features will continue to slowly pull further to the northeast today. Some towering cumulus in showers will remain over coastal regions of Labrador toward the northern peninsula in Newfoundland in an unstable NW flow.

 

 

Regional Impacts

 

None

 

 

Roberta McArthur

Convective Outlook Valid for July 17th, 2019

Convective Discussion

 

There is the potential for marginally severe thunderstorms to develop for parts of Atlantic Canada as a trough of low pressure swings through the region today and overnight.

 

A low pressure system over northern Quebec will move into Labrador by this evening. A cold front extends southward from this low and will track through all of the Atlantic provinces today into tomorrow morning. The primary concern for severe weather today will be ahead of and along the cold front as it moves over parts of central Labrador and central New Brunswick this afternoon and evening.

 

For New Brunswick, there will be plenty of low level moisture with dew points already reaching 20C and precipitable water values approaching the low 40s in southern Maine and over southwestern Nova Scotia. There is an area of showers starting to push into western New Brunswick but the cloud already over the area may inhibit some daytime heating. Looking at areas father north which have had clearer conditions as well as the Caribou 12Z sounding, convective temperatures near 28C are expected to be reached. CAPE values could reach the  1000-1500 J/kg range. Wind shear is mainly unidirectional but moderate enough to sustain potentially severe lines of convection with strong wind gusts possibly reaching 90 km/hr and heavy downpours. Freezing levels are quite high at 14,000ft but given the high CAPEs there could also be the risk for small hail <2cm.

 

Convection has also begun to initiate over northern Quebec and is expected to continue into central Labrador. The precipitable water values are not as high nor is the mid level shear but the freezing levels are lower so there is the risk for small hail.

 

 

Regional Impacts

 

 

New Brunswick…Locally heavy rainfall, frequent lightning, small hail and strong wind gusts possible early this afternoon into this evening.

 

Nova Scotia and Prince Edward Island…Locally heavy rainfall and  brief wind gusts possible this afternoon and evening.

 

Labrador… Locally heavy rainfall, frequent lightning, small hail and strong wind gusts possible early this afternoon into this evening.

 

Roberta McArthur

 

 

 

 

 

Convective Outlook Valid for July 16th, 2019

Convective Discussion

 

A broad upper low over Newfoundland and eastern Labrador will slowly drift to the northeast today. A more concentrated area of convection this morning over the southeastern Grand Banks will continue off to the north and east this afternoon. With some partial clearing this morning over central and eastern Newfoundland and Labrador, convective temperatures are expected to be reached along with a bit of cooling aloft which will further destabilize the atmosphere and help to generate some convection this afternoon. CAPE values in to 200-500 J/kg range along with some weak to moderate shear and sufficient low level moisture will help to sustain convection. With freezing levels  below 10,000ft, some small hail along with locally heavy rainfall is not out of the question.

 

Meanwhile, a more potent low pressure system currently over James Bay will be advancing eastward over northern Quebec today with a trough of low pressure extending southward. A warm front will begin to affect parts of western Labrador this evening and overnight with some embedded thundershowers along it. Some embedded thundershowers are also possible early tomorrow morning for western Labrador with a very slight risk over western New Brunswick as the trough of low pressure associated with the low pressure system continues to advance eastward.

 

 

Regional Impacts

 

Labrador…

Locally heavy downpours, small hail and brief strong wind gusts are possible this afternoon over parts of central and eastern Labrador.

 

Newfoundland…

Locally heavy downpours, small hail and brief strong wind gusts are possible this afternoon over parts of central and southeastern Newfoundland.

 

Maritimes…

No convective weather expected today. However, a very slight risk of an embedded thundershower is possible early tomorrow morning over western New Brunswick with locally heavy downpours.

 

Roberta McArthur

 

 

Convective Outlook Valid for July 15th 2019

Convective Discussion

 

A chance of thunderstorms over much of Atlantic Canada.

 

There a few distinct areas for potential thunderstorm development today for the Atlantic Provinces. Overall we are looking a moderate amount of moisture with greater than 25 mm of precipitable water with weak cape (< 300 J/kg) and giving weak vertical velocities. The potential for severe weather is quite low, however, some locally heavy showers are possible giving 15 to 20mm of rain. There a small chance that Maritime thunderstorms could become organized giving a slightly higher potential for heavy downpours, due to training or clustered convection.

 

Longer lived storms are possible over eastern Newfoundland where the dynamics are more favorable with moderate shear and decent dynamics. These thunderstorms will not be surface based and this will limit the potential for severe weather there is a high amount of moisture but the storms will be moving quickly. 15 – 20mm is possible.

 

Regional Impacts

 

Labrador…

Low risk of garden variety thunderstorms though the interior regions. A higher potential area of convection will move into western Labrador this evening. Small hail < 10mm and wind gusts near 30 knots are possible.

 

Newfoundland…

Garden Variety thunderstorms with a possibility of 15-20mm should higher topped storms develop. Embedded thunderstorms east are unlikely to produce any severe weather however

 

New Brunswick and Nova Scotia …

Garden Variety thunderstorms with a possibility of 15-25 mm should organized  storms develop.

 

 

 

 

 

Mel Lemmon

Convective Outlook Valid for July 14th, 2019

Convective discussion

 

Severe thunderstorms expected across New Brunswick today and possibly over parts of Nova Scotia and western PEI. 

 

Conditions are lining up nicely today for thunderstorms, some of which could be severe.  Diffluence aloft will help enhance convective activity.  An upper trough tracking over western New Brunswick will bring PVA to the area and a bit more cooling aloft to an already rather cool upper atmosphere.  Good moisture at the lower levels will help fuel thunderstorms.  0-6 km wind shear is around 30 to 35 knots which should be enough to help maintain longer lived storm cells.  The limiting factor today is that there is a lot of mid level moisture which could inhibit some stronger cell growth.  Satellite shows partial clearing in the area so CAPE values of 500-1000 J/kg are possible with higher amounts possible over the orange threat area where the timing of the trough this afternoon coincides with max heating.  The trough will help kick these thunderstorms and it is slow moving so heavy local rainfall is the main threat.  Strong, gusty winds and small hail are also possible.  The threat weakens this evening with the setting of the sun.

 

Regional impacts

 

New Brunswick: Heavy local rainfall is the main threat but strong, gusty winds and small hail also possible.

 

PEI: Western areas -> Heavy local rainfall is the main threat but strong, gusty winds and small hail also possible.

 

Nova Scotia: heavy local rainfall possible along the valley and east.

 

Newfoundland and Labrador: non severe expected over western Labrador.

 

Barrie MacKinnon

 

Convective Outlook Valid for July 13th, 2019

Convective discussion

 

Risk of non-severe thunderstorms over New Brunswick with small possibility of a severe thunderstorm. 

 

Partially clearing skies over New Brunswick with decent low level moisture  and weak surface convergence could produce thunderstorms over the area this afternoon and early evening.  Slight cooling aloft during the afternoon with marginal shear at around 30 kts and  some upper diffluence could be enough to maintain isolated severe thunderstorms with locally heavy downpours and strong, gusty winds but this threat is marginal. 

 

Regional impacts

 

New Brunswick: Thundershowers with small risk of a severe thunderstorms producing locally heavy downpours and strong, gusty winds.

 

PEI: Risk of non-severe west.

 

Nova Scotia: No thunderstorms expected.

 

Newfoundland and Labrador: No thunderstorms expected.

 

 

Barrie MacKinnon

 

Convective Outlook Valid for July 12 2019

Convective discussion

 

A frontal trough is advancing over the Maritimes. Area soundings from this morning are showing moisture extending from the low levels to 7,000-10,000 m. A southerly 40kt low-level-jet is feeding moisture, but the air mass is stable in the mid-levels limiting any thunderstorm activity to areas where Dew point temperatures are 20 degrees or more  (south of a line from northern Gulf of Maine to Lurcher to NS South Shore). The low pressure centre will move out of the Maritimes late Saturday, and at that point it will begin to impact NF.

 

Further west, over southern Quebec/Townships and Maine Highlands, the residual low-level cloud deck is starting to break up. This general area will be the focus for surface-based convection this afternoon. This is also where a surface-based moisture tongue is aligned with the 500 mb thermal ridge. Large CAPE values in excess of 1000 J/kg are indicated by the forecast guidance but are likely over-done due to the extent of the cloud cover. However, once the mid-level destabilize numerous clusters of thunderstorms could initiate. Slow eastward moving storms could produce brief heavy downpours and wind gusts. This activity could potentially reach westernmost areas of NB late this afternoon or early this evening.

 

Regional impacts

 

Newfoundland and Labrador: No thunderstorms expected.

 

New Brunswick: Risk of late-day thunderstorms brief downpours and high wind gusts possible.

 

PEI: No thunderstorms expected.

 

Nova Scotia: Isolated elevated non-severe thundershowers.

 

 

 

Convective Outlook Valid for July 11 2019

Convective discussion

 

No thunderstorms forecast today. Gradual clearing is expected over Newfoundland with the upper low departing to the southeast. Upper ridge continues to build over the Maritimes.

 

Moisture ahead of a trough extending from northern Quebec to the Great Lakes is starting to spill over Maine/NB. Rain with a risk of thunderstorms will spread across western Lab, NB, PEI and mainland NS Friday.

 

 

Convective Outlook Valid for June 10th, 2019

Convective discussion

This morning’s analysis is showing an upper cold low over the northeast coast of Newfoundland with a vast cloud deck extending southward to the south coast of the island. The upper air sounding indicates plenty of instability in the low to mid levels to produce widespread towering cumulus and showers. Limited daytime heating will produce enough energy (CAPE values between 250-500 J/kg)  to generate an isolated cumulonimbus over the areas where the southern edge of the cloud deck lies.

Regional impacts

Newfoundland and Labrador: Risk of isolated non-severe thunderstorms over Connaigre, Burin Peninsula, Clarenville and Terra Nova. Brief downpours, small hail and wind gusts 50 km/h.

New Brunswick: No thunderstorms expected.

PEI: No thunderstorms expected.

Nova Scotia: No thunderstorms expected.

Jean-Marc Couturier

Convective Outlook Valid for July 9, 2019

Convective Discussion

 

Only one area for potential TSRA is over NL and waters to the NE of the island. Upper level low and some PVA gave some elevated ISOL TSRA to parts of Newfoundland early this morning. Skies are beginning to clear somewhat, which could give way to some ISOL cells this afternoon. Modifying the 12Z tep from YJT could give between 200 and 300 CAPE, but the upper dynamics are weak. There could be slight 500 mb height falls which could lead to some cells. Freezing levels are low, so some small hail is a possibility if they develop. OTWZ nil sig wx for the rest of the region.

 

Regional Impacts

 

Newfoundland: ISOL cells are PSBL this afternoon.

 

Elsewhere: nil.

 

 

Jeremy

Convective Outlook Valid for July 8, 2019

Convective discussion

 

A couple areas show some potential for thundershowers/storms today. The first is a over the Quebec Lower North Shore. A weak trough near the surface could produce some TCU and am ISOL CB that could trickle into portions of the Great Northern Peninsula this afternoon.

 

The better area for possible storms is across SE QC this afternoon. WV imagery shows a good area of PVA east of James Bay that is advecting to the SE. Upper level troughing at 500/250 mb will give some weak divergence. There is also a decent jet at 250 upstream moving south of James Bay, and eventually curving towards the east, putting NRN NB/Gaspe in the left exit region (however the timing appears to be off just a little). Looking at KCAR and YZV, FZLVLs are below 10,000 feet, but PW is low as too the low level moisture. Shear, on the other hand, is pretty good. Expect strong gusty winds and small hail with the stronger storms this afternoon and into this evening. Given the decent dynamics, some cells will propagate over the GLFSTLAWR tonight.

 

Regional impacts

 

Newfoundland and Labrador: Risk for ISOL TSRA advecting from the Lower North Shore into the Northern Peninsula.

 

New Brunswick: SCTD non-severe storms are likely later today and into this evening associated with the PVA and upper level trough. Small hail and gusty winds are quite possible (conditions look ripe for some SVR storms in QC).

 

PEI: PSBL TSRA affecting portions of the island this evening as they move across ERN NB (good upper level forcing).

 

Nova Scotia: nil

 

 

Jeremy

Convective Outlook for Atlantic Canada Valid for July 7th, 2019

Convective Discussion

A quiet day across the Atlantic Region today as the cold front that produced the severe weather yesterday has moved out of the area. There will be some embedded thunderstorms along the cold front over the marine area that is quickly tracking eastward.

 

 

Regional Impacts

Non Expected.

 

 

Convective Outlook Valid for July 6, 2019

Convective Discussion

Non-severe thundershowers possible for much of Atlantic Canada, with possibly near severe impacts for northern and western Labrador this evening, for central New Brunswick for this afternoon possibly into this evening, and for northwestern Newfoundland.

All of this is related to an occluded low south of Ungava Bay, and a frontal system extending southwest from Labrador southwest into Maine. This is giving some dynamic support, mainly for New Brunswick for Today and Labrador for tonight. There’s some convection over Labrador ahead of the occluded low, and some insolation over the west. Dewpoints are a bit on the low side (10-15 C), but PWAT is in the 30 mm range, which isn’t bad. The upper jet approaching has some PVA, and when it sinks southeast there will be some enhanced lift from the Left Exit to the northwest. Shear is on the high side at 50+ kts, which isn’t likely to drop with the approaching jet, and will reduce local rainfall amounts, and may be too high relative to the CAPE to produce supercells.. The basic idea is that convection will persist into tonight.

For New Brunswick. Ingredients are healthy for convection, which may near severe status. Currently there is scattered convection in the clearer air ahead of the front, which may argue for more moderate cells. Moisture is good as the surface with 20C dewpoints, and at 850 mb  near 14C dewpoints. PWAT is near 50 mm. Instability is okay with CAPEs currently near 3-400 J/kg, and possibly a bit higher this afternoon. Later this afternoon CAPEs may near 500-1000 J/kg, which may be enough to near severe. The shear is currently near 30 kts, which is marginal for severe conditions,  but will increase a little this afternoon.

For Newfoundland the approaching front will act a bit like the conditions for New Brunswick, with marginal shear (30-40 kts) , probably lower CAPEs, slightly lower dewponts (near 16 C), and PWAT near 35 mm. Because of the timing and orientation of the trough, things should max out later in the afternoon roughly near the Deer Lake region.

Regional Impacts

Labrador: Non-severe thundershowers for most areas developing this afternoon with high intensity beginning this evening, with stronger cells north of the Labrador Highway and west of the mid Labrador coast. Impacts will be mainly local heavy downpours and some gusty winds. There may also be some hail further north.

Newfoundland: Non-severe thundershowers beginning early in the afternoon. Impacts will be local heavy downpours, followed by gusty winds. The Deer Lake region and points north on the Great Northern Peninsula should have more significant impacts.

Maritimes: Non-severe thundershowers today for New Brunswick and a chance for Prince Edward Island, with the most significant impacts for the southern half of New Brunswick  except for the Fundy Coast. For this evening a risk of thundershowers Nova Scotia. Impacts will be local heavy downpours and gusty winds.

Marine waters: Embedded convection possible for all Maritimes waters today and tonight, with stronger cells over southernmost waters. Also a slight chance near the Labrador Coast, and the Northeast Coast of Newfoundland.

Doug Mercer

Convective Outlook Valid for July 5, 2019

Convective Discussion

Near severe thundershowers  possible for  northern New Brunswick, with non-severe thundershowers possible for much of the Maritimes. Thundershowers possible for western Labrador and the Maritimes.

Maritimes: These will be mostly air mass driven by daytime heating up to the low thirties and dew points near 15-20 C . A deep ridge will move though New Brunswick this afternoon and over eastern Nova Scotia by this evening, having generally sunny conditions. CAPEs near or possibly exceeding  500 J/kg range are reasonable for the Maritimes provinces, with New Brunswick possibly in the 500-1000 J/kg range, and possibly higher central and north. The highest risk are for heavy downpours and high wind gusts. The main factors against these cells developing is a lack of moisture aloft, as well as a lack of upper support. 0-6 km shear is near 30 kts, and will diminish a bit this afternoon. Freezing levels near 13 to 15 thousand feet make significant hail unlikely.

Labrador: For western Labrador  there are two factors that may spawn some weak cells this afternoon, that may become healthier into early this evening. . Near or just east of Churchill falls there is a  north-south trough with some sunny breaks to the west. Farther west there is a weak diffluent upper jet approaching from Quebec.  These, combined with daytime heating may produce some cells with CAPEs up to 500 J/kg, with PWAT near 33 mm, and dew points near 14 C in the west. Wind shear is near 25 kts and will increase from the west into this evening to near 35-40 kts.

Regional Impacts

New Brunswick: : Near severe thundershowers possible this afternoon into this evening with heavy downpours and gusty winds possible.  Highest risk for severe in the north this afternoon.

Nova Scotia: Non-severe thundershowers possible this afternoon into this evening with heavy downpours and gusty winds possible.

Prince Edward Island: Non-severe thundershowers possible this afternoon with gusty winds and occasional heavy downpours.

Labrador: Non-severe thundershowers giving occasional downpours. A slight chance for small hail.

Newfoundland: None

Doug Mercer

Convective Outlook for Atlantic Canada valid for July 4th, 2019

Convective Discussion

 

Thunderstorms expected over eastern New Brunswick and parts of eastern Nova Scotia as well as western Labrador today.

 

The thunderstorms over the Maritimes will be primarily thermodynamically driven.  Lots of solar insolation today combined with good low level moisture will generate moderate CAPE values of around 500 J/kg however the lack of a triggering mechanism should restrain convective development to coastal areas where it will be influenced by a sea breeze and coastal convergence which should act as the kicker.  If thunderstorms develop along the coast, they will likely be slow moving so heavy local downpours will be the main threat.  Looking at satellite this morning, there seems to be a lot of forest fire smoke in the upper atmosphere.  This could impede convection as it will reduce solar insolation. 

For western Labrador, good low level moisture and solar insolation combined with cool temperatures aloft will bring CAPE values of around 500 J/kg.  There is a small possibility of severe thunderstorms being initiated; however, wind shear is quite insignificant, therefore thunderstorms cell will have difficulty maintaining themselves.

 

Regional Impacts

 

New Brunswick

 

Slow moving thunderstorms along the coast which could bring local heavy downpours.  Small hail and moderate winds also possible.

 

Nova Scotia

Slow moving thunderstorms which could bring local heavy downpours.  Small hail and moderate winds also possible.

 

PEI

None

 

Newfoundland & Labrador

For western Labrador,  local heavy downpours and moderate winds with a small chance of cells producing damaging winds. No impacts elsewhere.

 

 

Barrie MacKinnon

 

Convective Outlook for Atlantic Canada valid for July 3rd, 2019

Convective Discussion

 

Risk of thundershowers over western New Brunswick this afternoon and early this evening with no convective activity expected elsewhere.

 

Clearing skies over western New Brunswick will increase solar insolation which may be enough to trigger a few non severe thundershowers.  An approaching ridge  from the west brings subsidence to the area, so any convection that could get triggered should be  moderated due to the mid level stability.  Anywhere from 100 to 500 J/Kg can be expected over the area but, again, positive buoyancy should be limited to mid levels which should limit CB development.

 

Regional Impacts

 

New Brunswick

 

Scattered thundershowers possible over western NB but severe thunderstorms not expected.

 

Nova Scotia

None

 

PEI

None

 

Newfoundland & Labrador

None

 

 

Barrie MacKinnon

 

Convective Outlook for Atlantic Canada Valid for July 2nd, 2019

Convective Discussion

 

The main area of focus will be over Maine with surface based convection having already begun, this convection will spill into New Brunswick this afternoon. Overall dynamics for severe thunderstorms are not overly favorable however there weak surface trough with moderate amount of CAPE > 1000J/kg and high moisture. The main concern will be heavy downpours possibly exceeding 25mm hour and with the low freezing levels 2-3 cm hail is also possible. It is unlikely but some of this convection could move across weather Nova Scotia this evening.

 

Over Newfoundland some embedded CB’s ahead of the surface low pressure system will generate locally heave rainfall amounts.

 

Regional Impacts

 

Nova Scotia

Locally heavy downpours, 15 - 20 mm possible if thunderstorms move into Southwestern parts of the province this evening.

 

New Brunswick

Main concern will be over western regions with heavy downpours 20-25mm and moderate sized hail possible.

 

Newfoundland

Embedded thunderstorms ahead of the surface low could give locally heavier rainfall of 15 – 20mm. Over western Labrador very low topped thunderstorms could develop with some rain and small hail.

 

PEI

None

 

 

Convective Outlook Valid for July 1st, 2019

 

Convective Discussion

 

There are a few areas of convective potential for today into tomorrow morning. A slow moving upper low currently near Sable Island will continue to track eastward and stall just east of Cape Breton by this evening. Meanwhile, a trough currently over Hudson Bay will track eastward towards central Quebec and western Labrador this evening and reach northwestern New Brunswick by tomorrow morning.

 

Under the upper level feature south of Nova Scotia, most of the convection should remain over eastern coastal regions of Nova Scotia, Eastern Shore, Sable and marine waters farther east this afternoon and evening near the vicinity of the low centre. Due to the slow nature of this system, some areas are expected to get locally heavy downpours. A rainfall warning is in effect for Victoria county due to upslope enhancement in easterly winds. Precipitable water values remain in the 30-35mm range looking at the Yarmouth and Sable Island morning soundings. Winds should remain quite stable over the marine waters but any convection that makes it onshore may see brief wind gusts reaching 30kts. Rain could be heavy at times over southern Newfoundland today as the low continues to drift closer but the threat of convection is low.

 

Areas of western Labrador will see an increasingly unstable air mass this afternoon as weak troughing moves into the area and convective temperatures are expected to be reached to initiate surface based convection, especially over areas that have cleared out of the stratus early this morning. CAPE values could reach the 500-700 J/kg range but with weak shear this morning, generally pulse type storms are expected. Into late afternoon, however, the 0-6KM shear is forecast to increase from 20 to 30KT which may allow some thunderstorms could be maintained or possibly organize into small squall lines. This along with fairy low freezing levels may produce small hail, brief heavy downpours and strong gusts. Conditions are not expected to reach severe warning criteria.  The upper flow may hinder initially some of the surface based convection as well due to warming aloft as a warm front approaches the region from central Quebec. An extension of this trough will also make its way farther south toward Maine and northwestern New Brunswick by early tomorrow morning.

 

 

Regional Impacts

 

Nova Scotia…

Locally heavy downpours over eastern mainland Nova Scotia and Cape Breton

 

New Brunswick…

Isolated thunderstorms may affect northwestern New Brunswick early tomorrow morning.

 

Labrador…

Small hail, strong winds and locally heavy downpours are possible for western and central Labrador late this afternoon and overnight.

 

 

HAPPY CANADA DAY!

 

Roberta McArthur