Convective Outlook Valid for Today , Tonight and Tomorrow

Regional Impacts

 

Today:

NB: Scattered thunderstorms over central and southern regions. Some of these storms will likely be strong. The main threat will be very strong wind gusts of 70-90 km/h, and brief heavy downpours with rainfall rates of  20 mm/h

NL: Scattered thunderstorms mostly elevated over north-central regions of the Island ending this afternoon. Showers heavy at times with rainfall rates of 10-20mm/h

PEI: Risk of thunderstorms late this afternoon

NS: None

Lab: None

 

Tonight:

NB/PEI: Isolated thunderstorms ending

NL: Risk of thunderstorms over southern portions of the Island

NS: None

Lab: None

 

Sunday:

NS: Isolated thunderstorms developing with localized heavy showers

NL: Slight risk of thunderstorms over eastern regions

NB/PEI/LAB: None

 

 

Convective Discussion

 

At 12z this morning an upper trough extends from Hudson’s Bay to the lower Great Lakes, at the surface a low pressure system is located over the mouth of the St. Lawrence river with a warm front extending to central NF and a cold front extending southwestward over NE. Very warm and humid air prevails over the region with dewpoints ranging from 18-21 deg, and precipitable water between 30-40 mm. However dewpoints have been diminishing slowly over NW NB this morning, and this trend is expected throughout the area during the rest of the weekend. The low-level moisture was extending up to 300-400 m above ground this morning, but the latest satellite imagery is showing dissipation of the low level cloud. With full sunshine this afternoon, surface-based convection should initiate over southern NB where temperatures of 28-30 deg. are expected. In this modified environment, the potential energy will increase to about 1000 J/kg. Deep layer shear of around 30kt will likely lead to some clusters become somewhat organized into bands with a potential of low-key bow lines.

The convection over NF is associated with the warm front and much of the instability is above 850-700 mb level, CAPE of 400-500 J/kg are supporting this convection in an environment with precipitable water of ~40mm.

 

For Sunday, the weakening cold front should slowly move southeastward over NS and NF. The likelihood of thunderstorm activity is medium for Sunday afternoon

 

Thunderstorm Outlook for Today

 

Thunderstorm Outlook for Tonight

 

 

Thunderstorm Outlook for Tomorrow

Convective Outlook Valid for Today, Tonight and Tomorrow

Regional Impacts

 

Today:

NB: Near-severe thunderstorms possible over western and northern regions this afternoon and evening giving strong wind gusts (70 to 90 km/h), small hail and heavy downpours (20-40mm per hour rates).

NS/PEI/NL&LAB: None

 

Tonight:

NB: Thunderstorms possible overnight giving heavy downpours.

NL&LAB: Thunderstorms possible over southwestern Newfoundland and southwestern Labrador.

 

Saturday:

NB: Thunderstorms over central and southern regions this afternoon and evening giving heavy downpours.

NL: Thunderstorms over central to northern giving heavy downpours.

NS/PEI/LAB: None

 

 

Convective Discussion

 

An upper level trough extends from the Great Lakes northeast into the St. Lawrence River Valley with a surface low pressure developing this afternoon over central Quebec. Ahead of the trough over the Maritimes lies a warm and humid air mass with dewpoints remaining near 20C today over central to northern New Brunswick and precipitable water near 40 mm. Should there be sufficient clearing this afternoon, this may also provide additional surface based heat with temperatures into the high 20s with possible MUCAPE (upwards of 2000 J/kg) over central to northern New Brunswick. Caribou’s 12Z sounding indicates a capping inversion near 850mb but there is decent instability above.  With a 40KT 700mb jet and weak to moderate deep layer shear near 25KT, multicell development will likely occur over the higher terrain in north and central Maine (already ongoing this morning) and northwestern New Brunswick this afternoon. Cells may form into more organized lines as they track northeastward this afternoon and into the overnight. Given general northeast orientation of storm movement, there is the threat training and locally heavy downpours over the same locations. With sufficient mid-level instability, downdraft wind gusts and small hail with the more intense storms are also possible.

 

For Saturday, the trough inches slowly southeastward. The threat for severe thunderstorm development has decreased, but areas of central and southern New Brunswick could see heavy downpours in the afternoon and evening as well as northern Newfoundland.

 

Thunderstorm Outlook for Today

 

Thunderstorm Outlook for Tonight

 

Thunderstorm Outlook for Saturday

 

Forecaster: McArthur

 

Convective Outlook Valid for Today , Tonight and Tomorrow

***This will be the final scheduled outlook for the season.****

 

Regional Impacts

Today…

Eastern Labrador.. Slight risk of thunderstorms, some lightning possible.

Offshore Atlantic Marine areas and southeastern Newfoundland.. embedded thunderstorms possible.

 

Tomorrow… Slight chance of embedded thunderstorms.

 

Convective Discussion

It continues to be an interesting summer with most of the Atlantic region wedged between the remnants of Idalia and building ridge of high pressure. In terms of thunderstorm potential this will not be a very strong set up, however a weak upper trough could trigger some thunderstorms over eastern Labrador and west of the Maritimes in Quebec and Maine. As the moisture associated with Idalia creeps slowly northeastward there will be slight risk of a thunderstorm near the low. It is likely that most of the heavy precipitation will remain south of Nova Scotia, but there is a slight chance with higher PWAT value coming onshore over southeast Newfoundland that a few heavier showers could happen tonight and tomorrow. Tomorrow over Nova Scotia there will be a slightly enhanced chance of convection near the vicinity of the low pressure system, but the probability will remain quite low for heavier showers or thunderstorms.

 

Thunderstorm Outlook for Today

 

 

Thunderstorm Outlook for Tonight

 

Thunderstorm Outlook for Tomorrow

 

Mel Lemmon

Convective Outlook Valid for Today , Tonight and Tomorrow

Regional Impacts

 

Today:

Labrador: risk of a thunderstorm north of Labrador City/Wabush to Esker to Schefferville

 

Monday: None

 

Convective Discussion

An upper trough over Hudson’s Bay and an associated active cold front will move across northern Quebec today. A strong southwesterly low-level-jet is feeding moisture ahead of the surface feature. Precipitable water levels are currently between 30-35 mm. The cold front will reach western Labrador this evening. However, with the loss of daytime heating, forecast guidance is suggesting a weakening area of instability over the fp17hx area.

 

Thunderstorm Outlook for Today

 

Thunderstorm Outlook for Tonight

 

 

Thunderstorm Outlook for Tomorrow

Convective Outlook Valid for Today , Tonight and Tomorrow

Regional Impacts

None

 

Convective Discussion

The base of a cold upper trough in conjunction with the warm waters off western NL produced a few strikes and convective showers earlier this morning. However the upper trough is expected to continue progressing eastward with heights rising in its wake yielding stable conditions across all of Atlantic Canada. As such no thunderstorms are anticipated for the next 2 days.

 

Thunderstorm Outlook for Today

 

 

Thunderstorm Outlook for Tonight

 

 

Thunderstorm Outlook for Tomorrow

 

 

Allen

Convective Outlook Valid for Today , Tonight and Tomorrow

Regional Impacts

 

Today

NL/NS/NB/PEI/LAB: None

Southeastern Marine waters: Lightning and reduced visibility in heavy downpours.

 

Tonight

NL/NS/NB/PEI/LAB: None

Southeastern Marine waters: Lightning and reduced visibility in heavy downpours.

 

Friday

None

 

Convective Discussion

 

The UA at YYT this morning revealed the same tropical air mass that was in place across the Maritimes yesterday, with PWATs near 50mm. Instability exists aloft at ~850 mb but MUCAPE is limited (~150 J/Kg or less) due to some thermal ridging at the 500mb pressure level. This is also noted through the limited delta T between the 700 and 500mb levels of ~11-12 C, indicative of very little mid level instability. For this reason the no lightning is expected of land areas of eastern NL, however across the marine areas to the south and east of the Avalon higher MUCAPEs upwards of 500 J/Kg exist, and this should allow sufficient buoyancy and charge separation to produce isolated to scattered lightning today and tonight. Primary hazard for these mariners will be sharply reduced visibility in downpours.

 

By Friday this air mass is expected to move well to the east of the region and associated marine waters, with a much drier and stable air mass in its wake.  Stable conditions across Atlantic Canada are expected to last through Saturday at this time with no thunderstorms activity.

 

Thunderstorm outlook for today:

 

 

Thunderstorm outlook for tonight:

 

 

Thunderstorm outlook for Friday:

 

 

Allen

Convective Outlook Valid for Today, Tonight and Tomorrow

Today:

NS/NB/ PEI/NL: Embedded thunderstorms giving lighting and heavy downpours with rates of 50 mm per hour possible.

 

Tonight:

NS/PEI/NL&LAB: Embedded thunderstorms giving lighting and heavy downpours with rates of 50 mm per hour possible.

 

Thursday:

NS/NB/PEI/NL&LAB: None

 

Convective Discussion

 

A an area of low pressure is developing over New England and is expected to intensify as it tracks northeast across New Brunswick  and into the Gulf of St. Lawrence tonight and into the Labrador Sea by tomorrow night. Moisture has increased in the southerlies over Nova Scotia (50 to 60 mm precipitable water, Yarmouth’s 12Z has 57mm) which will push north and eastward over southern Newfoundland today. Embedded convection has already been occurring in the valley of Nova Scotia with observations near 40 mm per hour with continuing high rates of rain coming in from the Atlantic coast of Nova Scotia. Thunderstorms are also possible from the cold front which will track through Maine and towards western New Brunswick this afternoon and evening.  The threat of convection increases tonight and overnight as well for eastern Nova Scotia and southern Newfoundland as the cold front continues.  It does not appear that Hurricane Franklin, which is well south of the marine district, will interact much with this upper trough as it pulls further east. Regardless, there is still a chance that some added moisture from Franklin could get brought into the trough, enhancing rainfall amounts tonight into Thursday morning over southern Newfoundland.

 

There is a cool and dryer air mass behind this low for Thursday as a ridge of high pressure sets up over the Great Lakes and extends over the Maritimes for the end of the week and into the weekend.

 

Thunderstorm Outlook for Today

 

Thunderstorm Outlook for Tonight

 

Thunderstorm Outlook for Thursday

 

Forecaster: McArthur

Convective Outlook Valid for Today, Tonight and Tomorrow

Regional Impacts

 

Today:

NB/ NS / PEI / NL&LAB: None

Southern Maritime waters: Embedded thunderstorms with heavy downpours over the southern marine waters

 

Tonight:

NS/NB: Embedded thunderstorms giving lightning and heavy downpours

 

Wednesday:

NB/NS/PEI/NL: Embedded thunderstorms giving lighting and heavy downpours

 

Convective Discussion

 

A ridge of high pressure over Newfoundland will push east today as an upper trough of low pressure builds in from the west.  A trough extending from the Great Lakes towards Labrador will combine with a developing area of low pressure off Long Island today and tomorrow. There is also a weak frontal boundary today extending from central New York northeast into northwestern New Brunswick ,which is expected to give some TCUs or an isolated CB this afternoon and evening. With increasing 500mb temperatures moving into Maine, convection may be capped over northwestern New Brunswick, but some heavy downpours are still possible this evening. There will be an increase in moisture south of Nova Scotia (50 to 60 mm precipitable water) which will push northward tonight and Wednesday into Nova Scotia and eastward southern Newfoundland into Thursday. Embedded convection is likely with this system but there is uncertainty in how mid-level convection will materialize with the warm nose near 850mb and moisture profile between 700 and 500mb.  Meanwhile, Hurricane Franklin, which is well south of the marine district, may interact with this upper trough as it pulls further east, but there remains high uncertainty as well in whether the storm centre itself will be captured and quickly pulled east or will remain too slow and get left behind south of the marine district. Regardless, there is still a chance that some added moisture from Franklin could get brought into the trough, enhancing rainfall amounts tomorrow night.

 

Thunderstorm Outlook for Today

 

Thunderstorm Outlook for Tonight

 

Thunderstorm Outlook for Wednesday

 

Forecaster: McArthur

Convective Outlook Valid for Today , Tonight and Tomorrow

Regional Impacts

 

Today:

NL&LAB: Risk of thunderstorms, possibility of brief heavy showers and wind gusts 50-70 km/h

 

Tonight:

NB NS PEI NL&LAB: None

 

Tuesday:

NB NS PEI NL&LAB: None

 

Convective Discussion

An upper trough over the Gulf of St. Lawrence will swing through NF today, it pushing ahead at the surface is a cold front currently stretching from SErn Lab to WErn NF to Cabot Strait. There is extensive cloud cover near the front and some clearing/diurnal heating will be required to destabilize the air mass. In terms of other forcing mechanism, a cyclonic upper jet btn 80-100kt is analysed over NF this morning. The moisture plume which had been impacting the region on the weekend has moved off to the Grand Banks, and precipitable water values have diminished to 25-30 mm over the island, surface Td’s are btn 15-19 degrees which is still plenty to fuel some surface-based convection. The Stephenville sounding from 12z was used to estimate the convective potential for this afternoon: a Ts,Td combination of (20,16) yields MLCAPE values in the range of 400-500 J/kg, but the deep layer shear is on the high side, maybe to high to support initiation.

 

 

Thunderstorm Outlook for Today

 

 

Thunderstorm Outlook for Tonight

 

 

 

Thunderstorm Outlook for Tomorrow

RE: Convective Outlook Valid for Today , Tonight and Tomorrow

…Correction for the last panel below, it is valid for Monday…

 

Regional Impacts

 

Today:

NS: Widespread rain in the east with localised heavier showers with amounts up to 25 mm / isolated thunderstorms

NB: Slight risk of a thunderstorm SE

NL&LAB: Risk of a thunderstorm / widespread rain with embedded heavier showers along the southwest regions with amounts up to 50 mm

 

Tonight:

NB NS PEI: None

NL&LAB: Slight risk of a thunderstorm south coast

 

Sunday:

NB NS PEI: None

NL&LAB: Risk of thunderstorms eastern portions of the island

 

 

 

Convective Discussion

 

An upper low north of Sept-Iles with a trough extending to NB / Gulf of Maine will slowly swing eastward today and tonight,  eventually leaving NF coast Monday. At the surface, the low pressure is located NE of Anticosti island with a cold front extending to southern Maine. Elevated moisture content continues to be supplied  in the warm sector by a 40kt southerly LLJ, precipitable water values in the axis Sable-Cabot Strait-NF west coast are exceeding 45mm. YJT tephi from this morning indicates enough instability to support ACC/ACB with tops between 7-8 km. Over the Maritimes the airmass is beginning to dry but the instability and humidity is just enough to support one or two surface-based CB’s, based on the Shearwater modified tephi (24,18) Cape values could reach 300-400 J/kg LI -2 accompanied by strong deep layer shear 0f 30-40kt. A cyclonic 90kt upper jet stretching from southern NE to NF would also provide some extra forcing over NS.

 

Thunderstorm Outlook for Today

 

 

Thunderstorm Outlook for Tonight

 

 

 

Thunderstorm Outlook for Monday

 

 

 

 

Convective Outlook Valid for Today , Tonight and Tomorrow

Regional Impacts

 

Today:

NS: Widespread rain in the east with localised heavier showers with amounts up to 25 mm / isolated thunderstorms

NB: Slight risk of a thunderstorm SE

NL&LAB: Risk of a thunderstorm / widespread rain with embedded heavier showers along the southwest regions with amounts up to 50 mm

 

Tonight:

NB NS PEI: None

NL&LAB: Slight risk of a thunderstorm south coast

 

Sunday:

NB NS PEI: None

NL&LAB: Risk of thunderstorms eastern portions of the island

 

 

 

Convective Discussion

 

An upper low north of Sept-Iles with a trough extending to NB / Gulf of Maine will slowly swing eastward today and tonight,  eventually leaving NF coast Monday. At the surface, the low pressure is located NE of Anticosti island with a cold front extending to southern Maine. Elevated moisture content continues to be supplied  in the warm sector by a 40kt southerly LLJ, precipitable water values in the axis Sable-Cabot Strait-NF west coast are exceeding 45mm. YJT tephi from this morning indicates enough instability to support ACC/ACB with tops between 7-8 km. Over the Maritimes the airmass is beginning to dry but the instability and humidity is just enough to support one or two surface-based CB’s, based on the Shearwater modified tephi (24,18) Cape values could reach 300-400 J/kg LI -2 accompanied by strong deep layer shear 0f 30-40kt. A cyclonic 90kt upper jet stretching from southern NE to NF would also provide some extra forcing over NS.

 

Thunderstorm Outlook for Today

 

 

Thunderstorm Outlook for Tonight

 

 

 

Thunderstorm Outlook for Sunday

 

 

 

 

Convective Outlook Valid for Today, Tonight and Tomorrow

Regional Impacts

 

Today:

NS&PEI: Scattered heavy downpours. Strong wind gusts are also possible for western NB in the evening.

NB: Isolated heavy downpours and strong wind gusts for western NB in the evening.

NL&LAB: None

 

Tonight:

NS&PEI: Scattered thundershowers giving locally heavy downpours.

NB: None

NL&LAB: Isolated heavy downpours for southwestern Newfoundland.

 

Sunday:

NS: Isolated heavy downpours over eastern areas.

NL&LAB: Isolated heavy downpours for southern Newfoundland.

 

 

Convective Discussion

 

A trough of low pressure extends over the Maritimes northeastward into central Labrador giving heavy downpours at times. The trough will slow down today as it gets blocked against a ridge of high pressure east of Newfoundland and a building ridge over central Quebec. This will increase the threat of training showers or thunderstorms this afternoon and overnight, enhanced by a 40KT LLJ which will be slowly tracking along the Atlantic coast of NS. Rainfall rates of 25 to 50 mm per hour are possible as precipitable water increases over the Maritimes but there is uncertainty in the amount of lightning expected versus just tropical downpours, which will make rainfall amounts highly variable. Areas of southern New Brunswick, aided by topographic enhancement in strong southerly winds, have already seen total rainfall amounts of 50 to 90 mm overnight and this morning. Meanwhile, a trough over southern Quebec will shift southeastward into Maine and western New Brunswick this afternoon and evening. Although there is increasingly favourable dynamics in that area under the left exit of the 250mb jet and effective shear near 30KT, CAPE remains fairly weak. The strength of any thunderstorms that do develop will be conditional on if  cloudiness and showers from this morning clear. At this time, thunderstorms that do develop may not maintain for long, but there is still a small risk of organization into lines where strong wind gusts are possible.

 

For Sunday, the trough weakens as it slowly pulls eastward. Heavy downpours are possible for much of Newfoundland and southeastern Labrador. Where clouds clear out in the afternoon in Nova Scotia, convection may develop along the spine and drift southeastward.

 

Thunderstorm Outlook for Today

Thunderstorm Outlook for Tonight

 

 

 

Thunderstorm Outlook for Sunday

 

Forecaster: McArthur

 

 

Convective Outlook Valid for Today, Tonight and Tomorrow

Regional Impacts

 

Today:

None

 

Tonight:

NB/NS/PEI: Isolated thundershowers giving locally heavy downpours

NL&LAB: None

 

Saturday:

NB/NS/PEI: Scattered heavy downpours, especially into the evening hours. Strong wind gusts are also possible for western NB in the evening.

NL&LAB: None

 

 

 

Convective Discussion

 

Moisture from a frontal boundary advancing across central Quebec extending into central Labrador will combine with a short wave trough over New England which will push northeastward tonight into Saturday over the Maritimes. Some of this moisture has some tropical influence stemming from the remnants of Tropical Storm Hilary as it rounded a quasi-stationary ridge of high pressure over the central US. The upper levels are warm over Labrador today and given the current could cover, afternoon temperatures may not be high enough to break the cap. There could be a slight lightning risk, but regardless, some vigorous TCUs and isolated heavy downpours are expected today.  Another ridge of high pressure over Newfoundland and southeastern Labrador will suppress any convection today.

 

As the southern trough moves into the Maritimes tonight and into Saturday, the risk of isolated thunderstorms increases. Precipitable water of 40-50mm will also spread into Nova Scotia and the Gulf of St. Lawrence. The trough over the Maritimes on Saturday will slow down as it gets blocked against the ridge east of Newfoundland. This will increase the threat of training showers or thunderstorms especially for Saturday night. Rainfall rates of 25 to 50 mm per hour are possible but there is uncertainty in the amount of lightning expected versus just tropical downpours which will make rainfall amounts highly variable. Meanwhile, the trough over central Quebec will shift southeastward into Maine tomorrow afternoon. Increasing CAPE and effective wind shear over that area could see some convection organize into lines and move into western New Brunswick by the evening.

 

Thunderstorm Outlook for Today

 

Thunderstorm Outlook for Tonight

 

Thunderstorm Outlook for Saturday

 

Forecaster: McArthur

Convective Outlook Valid for Today, Tonight and Tomorrow

Regional Impacts

NS, Cape Breton, eastern PEI: Thundershowers and showers this afternoon.

Western Labrador: Weak unorganized convection and showers tomorrow near the upper low center.

 

Convective Discussion

A frontal feature is transiting Nova Scotia now bringing showers and weak thundershowers to many areas of the province. This forcing will move offshore later today. Environmental shear has degraded quite a bit since the front cut thru NB earlier. Cape Breton (nearer the low center) still has 15-20kts of 0-6k to work with early this aft. This is where the most lightning activity is expected in the next 2hrs. Pwats are 35 in the model and 32 on actual soundings. However, cells are moving at a good pace, leading to only 5-10mm in the heaviest pockets of rain. Alerts are not likely today. Tomorrow is calmer behind the front in the less humid and cooler air mass. Labrador may see a few lightning strikes tomorrow simply due to proximity to the low feature. Severe weather is not expected.

 

Thunderstorm Outlook for Today

 

Thunderstorm Outlook for Tonight

 

Thunderstorm Outlook for Tuesday

 

Forecaster: TIRONE.

Convective Outlook Valid for Today , Tonight and Tomorrow

Regional Impacts

 

Today

Western Lab: isolated thunderstorms possible this afternoon and evening.

Eastern NL: elevated embedded thundershowers possible giving locally torrential downpours.

 

Tonight

NB/PEI: isolated thundershowers possible overnight and into early Monday morning.

 

Convective Discussion

 

A couple weak features will give the chance of thunderstorms today – one being the current trough slowly crossing NL and the other being the upper low/trough near western Lab. The 12Z tephi out of YYT has close top 50 mm PWAT indicating a super moist atmosphere, so any TCU or CBs that develop will drop locally torrential rainfall amounts in a short period of time. That would be the only concern to speak of today. There has been a little history of isolated lightning with this trough so one would expect the odd lightning strike anytime this afternoon and into this evening. The second feature near western Lab also has shown a little history of TS development, so isolated cells are possible especially this afternoon and early evening. We are getting late in the season for surface-based convection up at those latitudes but there is still enough solar insolation to support them.

 

Lastly the guidance has been hinting at possible convection in NB and perhaps PEI overnight tonight and early Monday associated with a short wave trough/surface cold front. Could be an isolated cell over NS Monday afternoon that is not currently depicted in the 36 hour prog.

 

Thunderstorm Outlook for Today

 

Thunderstorm Outlook for Tonight

 

Thunderstorm Outlook for Tomorrow

Jeremy

Convective Outlook Valid for Today , Tonight and Tomorrow

Regional Impacts

NB… Showers or thunderstorms with small hail giving 15-20 mm. funnel clouds possible in vicinity of coastlines.

NF… embedded thundershowers giving 25mm.

 

Convective Discussion

Well another day another passing trough of low pressure that will bring heavier embedded thunderstorms and showers to some areas. Areas in Nova Scotia saw up to 75mm of rain, despite the fact that the thunderstorm activity was somewhat less than past events. Rainfall rates could still be around 25mm per hour, with a slight chance of a thunderstorm. Behind this feature and ahead of the upper low, New Brunswick could see some thunderstorms or deeper showers giving heavy rainfall rates. These will likely be quite isolated in nature but there may be some enhancement over north areas. Cape values are generally low, less than 500 J/kg of mixed Cape and low freezing levels, giving small hail likely around 1 cm. There is some risk of funnel cloud formation near shorelines where some extra surface convergence is present, it is possible that some rotation could be very close to the surface. It should be noted that weak updrafts are not likely to produce severe or strong surface rotation or winds. No alerts are expected but it is possible that alerts could be issued if cells come in stronger than expected.

 

Thunderstorm Outlook for Today

 

Thunderstorm Outlook for Tonight

 

Thunderstorm Outlook for Tomorrow

 

Mel Lemmon

Convective Outlook Valid for Today, Tonight, and Tomorrow

Regional Impacts

 

Today:

NS: Embedded thunderstorms this evening west of Halifax, heavy downpours of 30-60 mm.

NB: Risk of embedded thunderstorms along the Fundy coast this evening, heavy downpours of 30-60 mm. Chance for an isolated thunderstorm in extreme NW NB this evening, locally heavy downpours of 25-50 mm.

PEI: Chance for embedded thundershowers to move into PEI before midnight, locally heavy downpours of 10-15 mm.

NL: None.

 

Tonight:

NS: Embedded thunderstorms along the Atlantic coast between Halifax and Cape Breton Island overnight, heavy downpours of 25-50 mm.

NB & PEI: Slight chance for embedded thundershowers overnight, locally heavy downpours of 10-15 mm.

NL: None.

 

Convective Discussion…

An upper low over southern Ontario this morning will slowly move east, interacting with a stream of tropical moisture off the eastern seaboard today. Embedded thunderstorms have been observed over New England and to the southeast of Cape Cod this morning. These storms will move northeast today, reaching the southwestern shores of the Maritimes by this evening. Ample jet support wrapping around the aforementioned upper low will aid in sustaining this convection as it approaches the Maritimes, and is expected to persist along the Atlantic coast of NS tonight. The 12Z Yarmouth sounding this morning indicated precipitable water values of 50 mm, with this number expected to build to 60-65 mm over much of NS this evening. With a high volume of moisture in the atmosphere, any significant instability could lead to torrential downpours in the area of interest. Currently, MUCAPE values are forecast to build upwards of 500-750 J/kg by this evening along the Atlantic coast. With these numbers in mind, torrential downpours will be the main threat, with 30-60 mm and rainfall rates upwards of 25 mm/h possible. These amounts may end up being higher if the mid-level instability increases, depending on how much upper and mid-level cold air wraps around the upper low over Ontario, so this will be something to closely monitor.

 

A second smaller area of interest closer to the upper low exists in extreme NW NB. Here, an isolated thunderstorm may develop over Maine where stronger dynamics are present, however significant instability may be a challenge to reach. Thus, there is only a slight risk for severe weather, with the main threat being locally heavy downpours of 25-50 mm.

 

Thunderstorm Outlook for Today

 

Thunderstorm Outlook for Tonight

 

Thunderstorm Outlook for Tomorrow

 

Copp