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