Convective Outlook Valid for Today , Tonight and Tomorrow

 

Regional Impacts:

 

Today

Labrador/NB/NS/PEI/Magdalen: A chance of non-severe thundershowers.

NL: None

 

Tonight

Labrador/NS/NL/PEI/Magdalen: A chance of non-severe thundershowers.

NB: None.

 

Tuesday

Labrador/NL/ Magdalen: A chance of non-severe thundershowers.  

NS/PEI/NL: None

 

Convective Discussion:

The base of an upper trough will gradually move eastward today. MLCAPEs will build into the 200-500 J/Kg range by the later afternoon hours with bulk shears ~ 30 kts, however low level shear is expected to be on the low side given the lack of any significant surface feature or jets, which should limit storm organization. The most frequent lightning activity is expected to be across west-central Labrador today, where vorticity advections will be strongest aiding ascent in addition to general instability. In the Maritimes initiation will be limited until there is sufficient surface heating in combination with cooler air aloft slowing moving into the region with the upper trough.

 

Tonight into tomorrow morning thunderstorms will be focused mainly across the gulf, reaching western NL by the morning hours. In the southern Maritimes shears of ~50kts are expected to be too strong for the weak instability (200-400 J/Kg) to yield any storms. Further north/east into NL and Labrador this is not expected to be a problem with bulk shears lower in the range of 20-35 kts, which should once again yield non severe storms mainly focused near the upper trough. It is possible some an isolated storm may move into northern NB from the Gaspe late in the afternoon, however probability is to low to consider at this time.

 

Thunderstorm outlook for today:

 

Thunderstorm Outlook for Tonight:

 

Thunderstorm Outlook for Tomorrow:

 

Convective Outlook Valid for Today , Tonight and Tomorrow

Regional Impacts:

 

Today

Labrador: A chance of non-severe thundershowers.

NB/NS/PEI/NL: None.

 

Tonight

Labrador: A chance of non-severe thundershowers.

NS/PEI/NL NB: None.

 

Monday

NB/PEI/Labrador: A chance of non-severe thundershowers.  

NS/NL: None

 

Convective Discussion:

Finally the warm and humid air mass has departed region.  A supportive upper trough and a weak surface trough will give a potential for thundershowers in western Labrador today and Monday. The same lingering trough set-up will give potential thundershowers over New Brunswick and western PEI on Monday. MLCAPE values near 500 J/kg are expected over Labrador today and over Labrador/New Brunswick on Monday. Shear values near 20 kts will limit the thunderstorm impacts to non-severe. Gusty winds to 60 km/h are possible.

 

Thunderstorm outlook for today:

 

Thunderstorm Outlook for Tonight:

 

Thunderstorm Outlook for Tomorrow:

 

Convective Outlook Valid for Today , Tonight and Tomorrow

Regional Impacts

 

Today

Central NL: likely some scattered  thunderstorms giving gusty winds and locally torrential downpours this afternoon and into early this evening.

 

Sunday

Western Lab: slightest risk of an afternoon thunderstorm in the Lab City/Wabush area giving heaving downpours.

 

Convective Discussion

 

The only area to watch today is in Newfoundland where a short wave trough and surface frontal trough will be pushing through this afternoon. While some things look good for near severe storms, others look to perhaps limit them – one of those is being the very strong shear (close to 60 knots from 0-6 km at YJT)...which could be too high. There is a good moisture in the low levels with a trigger in the form of a short wave trough and associated surface cold front. The instability is nothing to write home about, so that too could act as a caveat. Skies are beginning to clear in the favourable upstream region where thunderstorms typically form then advect east-northeastward. For now expect gusty winds to 70 km/h and locally torrential downpours. The fast-moving nature of the cells should limit excessive rainfall. Although not mentioned in the graphic, small hail is also possible given the FZLVL is just above 10kft at YJT. OTWZ nil sig wx expected in the region.

 

There is the slightest risk of a thunderstorm Sunday afternoon in the Lab City and Wabush area as a large scale upper trough slowly approaches from Quebec.

 

Thunderstorm Outlook for Today

 

Thunderstorm Outlook for Tonight

 

Thunderstorm Outlook for Sunday

 

Jeremy

Convective Outlook Valid for Today , Tonight and Tomorrow

Regional Impacts

 

Today

NB: risk of a severe thunderstorm producing strong winds, hail and torrential rainfall this afternoon and evening.

Western Lab/PEI: scattered thunderstorms possible later today giving gusty winds, small hail and torrential downpours.

 

Tonight

Western NL/NB/PEI/western Lab: scattered thunderstorms possible giving mainly torrential downpours.

 

Saturday

Central NL: scattered thunderstorms possible in the afternoon and evening giving gusty winds, small hail and torrential downpours.

 

Convective Discussion

The main area of focus today will be across parts of NB as a short wave trough slowly approaches from the southern Quebec area. The timing of this feature will be important to maximize the full extent of day time heating. However, the dynamics later today are really good, so any storms that form and move into the region could last for a number of hours. The 12Z KCAR tephi has 2 strong warm noses above the surface, but does show close to 50 knots of mean shear from the surface to 6 km. it’s likely the Maniwaki profile further upstream would be more representative of the air mass that will be approaching NB later this afternoon. Adjusting for a surface temperature of 28-29 yields over 1000 CAPE. Much like the KCAR sounding the wind shear is high. And there is no lack of low level moisture as the Tds are in the high teens. Once the surface front/500 mb short wave makes its way in numerous thunderstorms will form in southern QB/northern ME, and will be monitored as they get close to NB. Based on current SAT imagery the timing for the potential severe storms will be later this afternoon and into the evening hours. As already mentioned, the dynamics appear good so even with the sun setting individual cells could last well into the night. Elsewhere some scattered thunderstorm possible for western Labrador and a portion of the Maritimes that is further downstream from the more buoyant atmosphere.

 

Nighttime activity is likely across western NL and a portion of the Maritimes as some of the cells that develop today maintain themselves and continue moving generally eastward (aided with cloud top cooling). The main concern would be torrential downpours at this time.

 

The same short wave could give a strong storm or 2 across central NL Saturday.

 

Thunderstorm Outlook for Today

 

Thunderstorm Outlook for Tonight and Saturday morning

 

Thunderstorm Outlook for Saturday

 

Jeremy

Convective Outlook Valid for Today, Tonight and Tomorrow

Regional Impacts

 

Today:

NB: Scattered thunderstorms possible this evening over southern regions giving lightning, locally heavy downpours of 10-20 mm.

NS: Scattered thunderstorms possible this evening for western regions giving lightning, locally heavy downpours of 25-50 mm, small hail and 70-90 km/h wind gusts .

NL and LAB: Scattered thunderstorms possible through Labrador and parts of central NFLD today giving lightning, 1-2 cm hail, 70km/h wind gusts, and locally heavy downpours of 20-30 mm.

 

Tonight:

NB/PEI/NS: Scattered thunderstorms possible tonight giving locally heavy downpours of 20-30 mm.

LAB: Isolated thunderstorms for eastern area giving locally heavy downpours.

 

Friday:

NB: Scattered thunderstorms giving lightning, locally heavy downpours, small hail, and strong wind gusts.

LAB: Isolated thunderstorms giving lightning, locally heavy downpours, small hail, and strong wind gusts.

 

Convective Discussion

There are a couple of different features to track of interest today. An intense short wave trough that affected southern Ontario yesterday is moving over New England today and eastward towards the Maritimes tonight. Ahead of this trough, afternoon instability will increase along with moisture over southern New Brunswick and Nova Scotia. Although the main threat of severe weather remains west over New England given the dynamics and the timing of this feature, convection could persist into the overnight hours. An approaching 30KT 850mb jet, moderate 0-6km shear, and cloud top cooling will also aid in continued risk of convection overnight, giving the risk of lightning and heavy downpours into Friday morning as the trough axis exits east of Cape Breton.

 

An upper low over northern Quebec will shift southeastward across Labrador today and out over the Labrador Sea tonight with a trough extending southward into Newfoundland. Convection occurring this morning east of the low centre will persist into this afternoon. An area of concern lies in central to southeastern Labrador (left exit of a 250mb jet, an approaching 500mb cold trough, increasing moderate shear and MLCAPE values above 1500 J/kg) such that convection that develops this afternoon with daytime heating could organize into multicell lines. Freezing levels are also lower which could increases the hail potential as well. There is also the possibility of embedded convection over Newfoundland from an area of moisture moving in from the Gulf of St. Lawrence this morning.

 

For Friday, the short wave trough exiting Cape Breton will affect portions of the marine waters south of Newfoundland. Meanwhile, the next short wave over central Quebec will be quickly tracking eastward towards New Brunswick and the Gulf of St. Lawrence by Friday night. Ahead of this trough in the afternoon, scattered thunderstorms are possible over northern New Brunswick and southwestern Labrador.

 

 

Thunderstorm Outlook for Today

 

Thunderstorm Outlook for Tonight

 

Thunderstorm Outlook for Friday

Convective Outlook Valid for Today, Tonight, and Tomorrow

Regional Impacts

NS: Isolated thundershowers possible this afternoon across mainland NS, locally heavy downpours of 10-20 mm. Chance of an isolated thunderstorm over the Cape Breton Highlands early this afternoon; 1-2 cm hail, 70-90 km/h wind gusts, and locally heavy downpours of 25-50 mm.

NB: Isolated thundershowers possible today, locally heavy downpours of 10-20 mm.

PEI: Isolated thunderstorm possible over eastern PEI early this afternoon; 1-2 cm hail, 70-90 km/h wind gusts, and locally heavy downpours of 25-50 mm.

NL: Scattered thunderstorms possible through west-central NFLD today; 1-2 cm hail, 70-90 km/h wind gusts, and locally heavy downpours of 25-50 mm.

 

Convective Discussion…

A small but intense shortwave trough moving through the Maritimes this morning brings the chance for sever weather across the eastern gulf of St. Lawrence and west-central NFLD today. Models have been struggling to resolve the intensity of this trough, with some strong storms having already moved through PEI and Iles-de-la-Madeleine this morning. These storms have weakened slightly as they moved over cooler gulf waters, but may re-intensify as they approach Cape Breton and the western shores of NFLD early this afternoon. Upper dynamics will allow for sustained convection over west-central NFLD, with a 110 kt 250 mb jet over the region. Bulk shear of 30-40 kts and SBCAPE values in excess of 1000 J/kg provide an ample environment for severe weather potential with the incoming shortwave trough acting as the main trigger. These storms will move northeast into north-central NFLD by this evening. The main threats with these storms will be pea to dime size hail, strong wind gusts reaching 70-90 km/h, and locally heavy downpours of 25-30 mm per hour.

 

In addition, isolated pop-up thundershowers are possible across the Maritimes this afternoon. Due to a lack of upper support however, these storms are expected to have short life spans, with the main threat being brief heavy downpours.

 

Thunderstorm Outlook for Today

 

Thunderstorm Outlook for Tonight

 

Thunderstorm Outlook for Tomorrow

 

Copp

Convective Outlook Valid for Today, Tonight, and Tomorrow

Regional Impacts

NS: None.

NB: A few thunderstorms possible over western and northern NB this afternoon; 1-2 cm hail, 70-90 km/h wind gusts, and locally heavy downpours of 25-50 mm.

PEI: Slight chance for an isolated thundershower over western PEI this evening, locally heavy downpours of 15 mm possible.

NL: A few thunderstorms possible between Goose Bay and Labrador City this afternoon; 1 cm hail, 70 km/h wind gusts, and locally heavy downpours of 20-40 mm.

 

Convective Discussion…

A small shortwave moving through eastern Quebec this morning will bring the risk for severe weather across parts of northwestern NB and central Labrador today. In NB, SBCAPE values are expected to climb upwards of 1500 J/kg this afternoon. This, in combination with bulk shear values of 30-40 kts will provide an ample environment for the development of severe weather. Dew points in parts of New Brunswick have been observed to be slightly higher than models have forecast this morning, as such SBCAPE values may be slightly higher than models are currently predicting. The main threat with these cells will be small hail of 1-2 cm, strong wind gusts of 70-90 km/h, and locally heavy downpours upwards of 25 mm per hour.

 

In central Labrador, SBCAPE values will be similar to those in NW NB, 1500-2000 J/kg between Labrador City and Goose Bay. Bulk shear here is slightly weaker however, in the 20-30 kt range, nonetheless a 40 kt 500 mb jet over the region will aid in sustaining organized convection this afternoon and into this evening. There is a chance these storms make it to Goose Bay by late this evening, however the main threat area is to the west of here. The hazards associated with these storms will be 1 cm hail, 70 km/h wind gusts, and locally heavy downpours of 20-40 mm.

 

Thunderstorm Outlook for Today

 

Thunderstorm Outlook for Tonight

 

Thunderstorm Outlook for Tomorrow

 

Copp

RE: Convective Outlook Valid for Today , Tonight and Tomorrow

*** Updated Thunderstorm Outlook for Tuesday. See image below ***

 

Regional Impacts

NB NS PEI: none.

NF: Scattered thunderstorms, possibly strong later this afternoon, localized downpours of 15 mm, small hail, and gusty winds near thunderstorms.

 

Convective Discussion…

The plume of tropical moisture has now moved east of NF. At 500mb, a trough extends from the James Bay region to the Gulf of St. Lawrence, leaving NF in a fairly unstable airmass. Precip. Water calculated from the area soundings are ranging from 30 to 50 mm, except for AYT (55 mm) which has some residual tropical moisture. VIL of the day guidance is showing values of 35-50 kg/m^2 - fairly strong updrafts and large CAPE values are in store in today’s environment which may lead to some small hail.  

A 90kt southwesterly upper jet extending from NS to the Avalon will add some dynamic for some stronger surface-based convection over the region. Moderate unidirectional deep layer sheers will also provide an opportunity for some clusters of thunderstorms to semi-organize.  

Tomorrow, the environment found over QC/NE US will advance over NB and Lab.

 

Thunderstorm Outlook for Today

 

Thunderstorm Outlook for Tonight

 

Thunderstorm Outlook for Tomorrow

 

Convective Outlook Valid for Today , Tonight and Tomorrow

Regional Impacts

NB NS PEI: none.

NF: Scattered thunderstorms, possibly strong later this afternoon, localized downpours of 15 mm, small hail, and gusty winds near thunderstorms.

 

Convective Discussion…

The plume of tropical moisture has now moved east of NF. At 500mb, a trough extends from the James Bay region to the Gulf of St. Lawrence, leaving NF in a fairly unstable airmass. Precip. Water calculated from the area soundings are ranging from 30 to 50 mm, except for AYT (55 mm) which has some residual tropical moisture. VIL of the day guidance is showing values of 35-50 kg/m^2 - fairly strong updrafts and large CAPE values are in store in today’s environment which may lead to some small hail.  

A 90kt southwesterly upper jet extending from NS to the Avalon will add some dynamic for some stronger surface-based convection over the region. Moderate unidirectional deep layer sheers will also provide an opportunity for some clusters of thunderstorms to semi-organize.  

Tomorrow, the environment found over QC/NE US will advance over NB and Lab.

 

Thunderstorm Outlook for Today

 

Thunderstorm Outlook for Tonight

 

Thunderstorm Outlook for Tomorrow

 

Convective Outlook Valid for Today , Tonight and Tomorrow

Regional Impacts

NB NS PEI: Isolated thunderstorms, giving localized downpours.

NF: Scattered embedded thunderstorms over western sections, torrential rain with 30-60 mm with the highest amounts in the southwest.

Lab: Scattered thunderstorms, possibly strong later this afternoon, localized downpours of up to 20 mm, small hail, and gusty winds near thunderstorms.

 

Convective Discussion…

Satellite imagery shows the tropical moisture feed over western Newfoundland. Precip. Water calculated from the area sounding are ranging from 40 to 45 mm, VIL of the day guidance is showing values of 40-60 kg/m^2.  While convective inhibition is still fairly high over eastern parts of NF, in the west where the 500mb thermal through lies, embedded convection will continue to support moderate to heavy rain. A slightly cyclonic southwesterly 90kt upper jet will add some dynamic support for some stronger surface-based convection over Labrador. Moderate to strong deep layer sheers will also provide an opportunity for some clusters of thunderstorms to semi-organize.  

A 500mb through extends from Hudson’s Bay to the Gulf of Maine. This feature along with the upper jet and some limited insolation may provide enough energy/support for the development of isolated CB’s in the still very moist environment found over the Maritimes. Convective temperature is running around 28 for most of the areas – for areas with less cloud cover CAPE values will be approaching or even surpass 500J/kg at the peak of insulation later this afternoon. Tomorrow, the stronger convective activity will shift over eastern portions of the island of NF.

 

Thunderstorm Outlook for Today

 

Thunderstorm Outlook for Tonight

 

Thunderstorm Outlook for Tomorrow

Convective Outlook Valid for Today, Tonight, and Tomorrow

Regional Impacts

NS: Embedded thunderstorms today, torrential downpours of 30-50 mm in convection.

NB: Isolated thundershowers possible this afternoon, locally heavy downpours of 10-15 mm.

PEI: Embedded thundershowers possible this afternoon, locally heavy downpours of 10-15 mm.

NL: Isolated thundershowers possible over extreme northern Labrador, locally heavy downpours.

 

Convective Discussion…

A stream of tropical moisture has made its way into southwestern NS this morning. Embedded convection is expected to continue along this stream as it slowly moves northeast over the next few days, bringing torrential rain across much of the Atlantic coast. The 12Z UA sounding from Yarmouth indicated PWAT values of 42 mm, with this forecast to increase to near 50 mm by this afternoon between Yarmouth and Halifax. Rainfall warnings have been issued along the Atlantic coast of NS for total rainfall amounts of 40 to 70 mm, with possibly higher amounts in areas of more intense convection by tomorrow night.

 

Tomorrow, an additional area of interest exists in NW NB, associated with a low pressure system that brought widespread severe weather to southern Ontario yesterday. This low is forecast to slowly track northeast along the St. Lawrence river tomorrow. Significant cooling aloft and ample moisture in NB will allow for SBCAPE values to build to 2000 J/kg tomorrow afternoon, with convective temperatures around 23 degrees, making this a suitable environment for severe weather. Bulk shear values of 30-40 kts will allow for some sustained updrafts, with the potential for 1 to 2 cm hail with these storms. Strong wind gusts to 70 km/h and locally heavy downpours of 20-40 mm are also possible.

 

Thunderstorm Outlook for Today

 

Thunderstorm Outlook for Tonight

 

Thunderstorm Outlook for Tomorrow

Copp

Convective Outlook Valid for Today, Tonight, and Tomorrow

Regional Impacts

NS: Pop-up thundershowers possible in central NS this afternoon. Locally heavy downpours of 10-15 mm.

NB: Pop-up thundershowers possible in SE NB this afternoon. Locally heavy downpours of 10-15 mm.

PEI: None.

NL: Embedded thundershowers possible for south-central NFLD. Heavy downpours of 20-40 mm.

 

Convective Discussion…

The main threat for severe weather today exists with an embedded low currently moving into Banquereau waters towards NFLD. Strong upper dynamics and mid level instability will support convection as this low approaches NFLD this afternoon. No lightning has been detected, however the feature remains highly convective with rainfall rates over 25 mm/hour possible. This feature is forecast to quickly weaken once it reaches the southern coast of NFLD later today.

 

A few pop-up thundershowers are also possible in central NS and SE NB this afternoon. Warm, moist air will bring SBCAPE values near 1500 J/kg which will aid in the development of convection this afternoon, a lack of upper level support however, should hinder the life span of any storm that initiates. Locally heavy downpours of 10-15 mm will be the main threat with these cells.

 

On Friday, another stream of moisture from the tropics will move into southwestern NS. Embedded convection within this moisture stream will lead to locally heavy downpours. PWAT values are forecast to build to 40-50 mm by the afternoon, so rainfall rates upwards of 25mm/hr are not out of the question.

 

Thunderstorm Outlook for Today

 

Thunderstorm Outlook for Tonight

 

Thunderstorm Outlook for Tomorrow

 

Copp

Convective Outlook Valid for Today, Tonight, and Tomorrow

Regional Impacts

 

Today

NS: Embedded thunderstorms with locally heavy downpours >25 mm/hr possible today.

NB: Isolated thunderstorms over NW NB, 70 km/h wind gusts, 1-2 cm hail, and locally heavy downpours >25 mm/hr possible this afternoon.

PEI: None.

NL: Isolated thundershowers over Labrador and western NFLD today, embedded thunderstorms with locally heavy downpours >25 mm/hr possible over the Port-Aux-Basques region this evening.

 

Thursday

NS: None.

NB: None.

PEI: None.

NL: Embedded thunderstorms possible over central NFLD tomorrow, with locally heavy downpours >25mm/hr possible.

 

Convective Discussion…

Two main areas interest for potential severe weather exist today. The first threat area is associated with a trough moving through Nova Scotia today. Within this trough we are likely to see some embedded convection, with heavy downpours being the main risk. PWAT values from the Yarmouth sounding this morning indicated 45 mm, this is forecast to build to 50-60 mm by this afternoon east of Halifax. Bulk shear values of 40-50 kts will aid in sustaining this convection today as it moves east, reaching the Port-Aux-Basques region of NFLD by this evening. Total rainfall amounts may be in the range of 30-60 mm in areas of strongest convection, with rainfall rates of >25 mm/hr possible.

 

The second area of interest is in NW NB, which is associated with a small vorticity centre that is forecast to track along the Gaspe Peninsula this afternoon. This vort max has already spawned a severe thunderstorm near Saguenay, QC, with some weaker echoes popping up to the south near Maine. A relatively strong 250 mb jet over NW NB should aid in the intensification of some of these southern cells as they approach the NB border this afternoon. SBCAPE values upwards of 1500 J/kg and bulk shear values of 40-50 kts in this region will allow for some of these storms to potentially become severe as they enter NB. Small hail (1-2 cm), gusty winds (70 km/h), and brief but intense downpours (>25mm/hr) will be the main threats associated with these cells.

 

Tomorrow, the aforementioned trough moving through NS today will bring the threat for some embedded convection with locally heavy downpours to central NFLD. PWAT values are expected to be slightly lower tomorrow, in the 40-50 mm range. The main threat will once a gain be heavy rain, with rainfall rates of >25mm/hr possible.

 

Thunderstorm Outlook for Today

 

Thunderstorm Outlook for Tonight

 

Thunderstorm Outlook for Tomorrow

 

Copp

Convective Outlook Valid for Today and Tomorrow

Tuesday, July 18, 2023

Regional Impacts

 

Today

NB: Gusty winds, small hail and downpours, rainfall rates >25mm/hr.

NS: Downpours begin this evening, rainfall rates >25mm/hr.

LAB: Isolated lightning

 

Tonight

NB: Downpours, rainfall rates >25mm/hr

NS: Downpours, rainfall rates >25mm/hr

PEI: Downpours, rainfall rates >25mm/hr

Magdalen Islands: Downpours, rainfall rates <25 mm/hr

LAB: Isolated lightning.

 

Wednesday

NS: Downpours, rainfall rates> 25mm/h

NL: Downpours, rainfall rates> 25mm/h

LAB: Scattered lightning

NB: isolated lightning.

 

Convective Discussion

UA’s from Caribou, Yarmouth and Maniwaki indicated only modest PWATs of 26, 32 and 20 mm respectively at 12z. Nevertheless moisture is anticipated to rebuild ahead of a weakening cold front in NW NB throughout the afternoon. Thunderstorms are expected to initiate ahead of this feature in eastern Quebec and Northern Maine and move into Madawaska and western parts of Restigouche County late this afternoon. Storms will have SBCAPEs of 1000-1500 J/kg to work with following peak insolation (assuming minimal impacts from smoke in the vicinity). Bulk shears of 35-45 kts, of primarily linear character will allow storms to sustain themselves and grow into multi-cells that could present the odd strong downdraft to bring gusty winds. In addition PWATs are expected to build to ~ 40mm by late this afternoon yielding primary hazards of rainfall rates, and gusty winds in this region of NB. Small hail is also possible, however the hail threat will be limited by less than ideal buoyancy through the HGZ, given high freezing levels, despite the favourable shear character.

 

A broad upper trough well to the west of the region has begun to take on a negative tilt, this will guide a new stream of tropical moisture into southern NB and western NS by the evening hours. Models suggest PWATs building up to 65mm during the overnight hours. Moist unstable profiles will be aided by a broad ascent region associated with the right entrance of an upper jet. Lightning with this stream of moisture will initially be isolated, but should become more frequent overnight with cold top cooling as this band of moist unstable air slowly moves east. Elevated MUCAPES of 500-1000 J/Kg, should yield torrential downpours, with localized flooding being possible throughout the overnight in southern NB, parts of PEI and the western half of mainland NS.

 

On Wednesday this same area of moisture will present a similar downpour threat for eastern NS and western NL, although lightning frequency may be lower during the daytime hours as cloud tops warm. Northern NB and much of Labrador can expect air mass thunderstorms of isolated to scattered frequency respectively due to a cooler air mass aloft moving eastward from James Bay.

 

 

Thunderstorm Outlook for Today

 

Thunderstorm Outlook for tonight:

 

 

Thunderstorm Outlook for Wednesday:

 

 

 

 

Allen

Convective Outlook Valid for Today and Tomorrow

Monday, July 17, 2023

 

Regional Impacts

 

Today

NB: Isolated thunderstorms possible producing gusty winds.

LAB: Isolated lightning

 

Tonight

NB: Isolated lightning

 

Tuesday

NB: Thunderstorms with downpours with rainfall rates of 15-25mm/h

LAB: isolated lightning

 

Convective Discussion

A broad area of ascent driven by a surface trough, vorticity advections and favourable upper jet dynamics will drive isolated storms later this afternoon across parts of northwestern Labrador.

In the Maritimes today a trough will continue to advect eastward throughout the day. Elevated instability exists near and east of the trough, with high PWATs thin MUCAPE profiles of 200-300 J/KG, however due to the proximity of a mid tropospheric thermal ridge very high freezing levels exist. As a result, buoyancy looks to be limited through the ICN, thereby limiting charge separating and lightning. Regardless downpours may produce rainfall rates of 15-25mm/hr, despite no lightning being expected along this feature.

 

Behind the trough in NW NB, clearing and residual moisture in the PBL will yield MLCAPEs near 1000 J/Kg, with moderate shear profiles. However beyond surface heating there is a lack of a dynamic triggering mechanism which should temporarily delay initiation and limit the number of storms that do develop. The Mid to upper troposphere does dry significantly by the late afternoon and early evening, supported by observations upstream (12z Maniwaki UA). This favours a wind hazard for storms (DCAPEs 700-1000 J/Kg), while limiting the risk for heavy downpours. Storms will weaken late this evening, but may exist just after midnight before dissipating.

 

On Tuesday deep moisture rebuilds ahead of an shortwave moving eastward from Southern Quebec, this will yield a downpour threat for NW NB. Despite lower CAPEs, this synoptic trigger should allow for a greater prevalence of storms and lightning compared to today.

Cool air aloft and differential heating in the terrain in northern Labrador may also produce some localized lightning.

 

Overnight Tuesday into Wednesday this deep moisture will move eastwards along a trough and any storms that develop will bring the risk of heavy downpours.

 

 

Thunderstorm Outlook for Today

 

Thunderstorm Outlook for tonight:

 

 

Thunderstorm Outlook for Tuesday:

 

 

Thunderstorm Outlook for Wednesday:

 

 

 

Allen

Convective Outlook Valid for Today, Tonight and Tomorrow

Sunday, July 16, 2023 11:49 AM

Regional Impacts

 

Today

NB: Heavy downpours, with intense rainfall rates of 25 to 50 mm/h and locally strong wind gusts.

Labrador: Scattered thunderstorms over central and southeastern Labrador giving heavy downpours, small hail and strong winds.

NS: None.

PEI: Risk of downpours for Prince County.

 

Tonight

NB: Heavy downpours with isolated embedded thunderstorms. Rainfall rates of 25 to 50 mm/h.

NS: Heavy downpours possible for the Atlantic coast and western regions.

 

Monday

NS: Heavy downpours likely for western and central regions with rainfall rates at 25 to 50 mm/h.

NB: Isolated to scattered thunderstorms with intense rainfall rates of 25 to 50 mm

 

Convective Discussion

An upper low currently over James Bay will slowly weaken and track eastward as a quasi-stationary ridge holds over Newfoundland extending towards the Grand Banks. The Maritimes remains under a tropical air mass with precipitable water between 40 and 50 mm. An area of heavy showers this morning over the Bay of Fundy into southern New Brunswick will continue to push northward this afternoon. The trough associated with the low over James Bay is giving multiple rounds of heavy rainfall in southern Quebec extending south that will slowly push into western New Brunswick overnight and into Monday over PEI and western NS Monday night. Persistent cloud cover over New Brunswick is not likely to allow any surface based convection today, but there is 25KT 0-6km shear from KCAR so along with heavy rainfall, some isolated strong wind gusts are possible if more organized lines develop.

 

Over central and southeastern Labrador today, some clearing of cloud this morning will allow temperatures to reach the convective temperature based off Goose Bay’s 12Z sounding and expected high reaching 30C with MUCAPES of near 1000 J/kg. Deep level shear is fairly week, so not expecting strong organization of any convection that develops, but with precipitable water also in the low 30’s so heavy downpours will be a factor.

 

Behind the trough on Monday, there air mass remains unstable with isolated thunderstorms possible for western New Brunswick and western Labrador.

 

Thunderstorm Outlook for Today

 

 

Thunderstorm Outlook for Tonight

 

 

Thunderstorm Outlook for Tomorrow

 

Convective Outlook Valid for Today , Tonight and Tomorrow

Regional Impacts

 

Today

NB: Scattered thunderstorms, slight risk of severe in multi-clusters/features in the north. Rainfall rates in excess of 25mm/h, gusts 60km/h, small hail and frequent lightning.

NF&LAB: Frequent thunderstorms over central and southern Labrador. Rainfall rates in excess of 15mm/h, gusts 70km/h, small hail and frequent lightning.

NS: Risk of thunderstorms producing downpours

PEI: None

 

Tonight

NB: Isolated thunderstorms possible  giving localized downpours.

 

Sunday

NB and Lab: Thunderstorms possibly giving strong wind gusts, heavy downpours, and frequent lightning.

 

Convective Discussion

At 12z the two large scales features of interest are an upper low on the western shores of Hudson’s Bay and a ridge along the NF coast. The thermal ridge is holding strong over NF where fair conditions continue to prevail. Convective temperatures for interior regions is 30+ which will likely not be reached however Cu/Tcu should develop. Over Labrador, a weak area of convergence will advance over central regions/Churchill Valley and become the focus for surface-based convection. If the extend of the cloud cover currently over the lower Churchill valley diminishes, warm temperatures will yield increase instability with cape values ranging from 500-800 J/kg, LI -3, but deep layer shear are less than 20 kt. The main threat would be downpours and high wind gusts.

Over the Maritimes, the tropical air mass continues to prevail with VIL values for today between 40-50 mm (up to 65 mm  over New England). Some of the clusters of thunderstorms have produced significant amounts of rainfall even during the night and that will continue today with the focus for the afternoon over northern NB. The steering flow will be southwest around 20kt.

 

Thunderstorm Outlook for Today

 

 

Thunderstorm Outlook for Tonight

 

 

Thunderstorm Outlook for Tomorrow