Convective Outlook Valid for Today, Tonight and Tomorrow

Regional Impacts

Today

NB: Some isolated thunderstorms are possible over western regions giving brief winds, heavy downpours and small hail.

Labrador: Some isolated thunderstorms are expected for western regions giving brief winds gusts and small hail.

NS/PEI/NL: None

Tonight

None.

Tomorrow

NB/NS/PEI: Risk of thunderstorms across NB in the afternoon into western NS and PEI in the evening giving brief wind gusts and heavy downpours.

Labrador : Scattered thunderstorms across central and southern regions from early afternoon to the evening giving brief wind gusts and small hail.

NL: None

Convective Discussion

As a low pressure system pulls east of Newfoundland this morning, weak ridging build across the eastern Maritimes, Newfoundland and southeastern Labrador today, limiting convection. To the west, a trough of low pressure will slowly advance southeastward from northern Quebec, with another trough of low pressure  across the Great Lakes. Two areas to watch today will be ahead of these two features as they enter western Labrador and western New Brunswick this afternoon. With MLCAPE of 500 J/kg and effective shear of 15-20kt, convection that develops is not expected to be that organized, but could still give be some brief wind gusts and small hail into western Labrador given low freezing levels. For the environment entering western New Brunswick, there is similar CAPE values but a bit more shear of near 35-30kt and precipitable water of near 25 mm, which could lead to some organization across southwestern areas this afternoon. Multicell or possible lines may develop and brief strong wind gusts and small hail are possible, although upper support remains further west today, so are not expected to reach severe limits.

For tomorrow, the ridge holds over Newfoundland, but the two troughs continue further east, with the northern trough over central Labrador and the southern trough across southern Quebec and into northern Maine by the evening. More widespread showers and thundershowers are expected for Labrador with some organization possible into multicell or lines as MLCAPE increased to 1000J/kg and effective shear increasing to near 30 kt. Small hail and strong wind gusts will be the main threats given it will be quite dry in the low levels. For the Maritimes, the trough advances towards Maine with some potential for more organized thunderstorms given increasing shear, but CAPE remains near 500J/kg. There is increasing precipitable water of 35 mm, leading to higher rainfall rates in embedded convection in the evening across southern New Brunswick and western Nova Scotia.

Thunderstorm Outlook for Today

Thunderstorm Outlook for Tonight

Thunderstorm Outlook for Tomorrow

Forecaster: McArthur

Convective Outlook Valid for Today, Tonight and Tomorrow

Regional Impacts

Today

NB: Thunderstorms are forecast to develop this afternoon and early evening. Severe storms are possible along and south of Highway 2, with gusty winds and moderate hail. (Depicted in yellow).

PE/NS: Some of these storms may survive across the Strait and Bay entering PEI/NS this evening in their late stages of development. They won’t be building any further at this point. (Depicted in grey)

Cape Breton/Avalon/Burin: Embedded -TS risk near noon and this afternoon along the Atlantic coast and offshore. Heavy rain occurring in areas, but no other hazards forecast.

Tonight

Atlantic: No thunderstorms forecast in the overnight time period.

Tomorrow

Western Labrador: Thunderstorms are forecast to re-develop in the afternoon and evening hours. Some may approach marginal severe limits.

NB: Western and northern areas of the province could see a few lightning strikes as thunderstorms re-develop in the afternoon. Not forecast as severe at this time.

Friday

NS: Western NS and the Annapolis Valley could see organized convection that approaches severe limits. This will be analyzed further in coming shifts.

 

Convective Discussion

There is ample moisture again today across the Maritimes. LL cloud/fog is expected to burn back in NB late this morning, setting the stage. Today, a forcing at the 500mb level is at play. This thermal trof is expected to sweep through NB this afternoon, and brings the chance of all hazards to areas in the province (depicted in yellow). MLCAPE sits near 1800J with Effective shear values 30-40kts. Watches will likely be issued in the area of Woodstock and Fredericton. Dewpoints across NS are also near 15 this AM, but there is a lack of a sfc forcing as the synoptic rain effects most of the central and eastern region at present. If a discrete line of storms is able to form in SW-SE NB, the biggest hazard is the wind threat. Gusts could be over 90km/h in an organized complex – storm motion to the ESE. These cells also may survive across the Northumberland Strait and Bay of Fundy with a strong 700 steering flow late day today. The grey hazard area is extended to reflect this evening risk. It should also be noted that helicity today is non-zero. This, along with low freezing levels, will be monitored closely.

Thunderstorm Outlook for Today

Thunderstorm Outlook for Tonight

Thunderstorm Outlook for Tomorrow

Forecaster: Tirone.

Convective Outlook Valid for Today, Tonight and Tomorrow

Regional Impacts

Today

NB: Chance of some scattered embedded thundershowers over southern New Brunswick this afternoon and evening with some locally heavy downpours.

Lab: Chance of scattered/frequent thunderstorms through southern Labrador today. These could be marginally severe with gusty winds and heavy downpours (locally).

NS: Scattered embedded thundershowers over most of mainland NS this afternoon and evening. Rain is the biggest hazard.

Tonight

NS: Thunderstorms continue over eastern sections as well as much of the marine district.

Tomorrow

NB: Thunderstorms are forecast to develop late afternoon and early evening. Severe storms are possible along and south of Highway 2, with gusty winds and moderate hail.

 

Convective Discussion

Labrador has lit up quite quickly today with lightning across the southern tier. These storms (spawning from a low centre anchored way back to the west) have a lack of a dominant steering flow and so they could drop quite a bit of rain locally. Elsewhere across the southern Maritimes, an embedded TS risk exists within the broader precip shield that has enveloped the region. Later this afternoon, greater jet support advances east from New England and should create enough lift and charge separation to spark more lightning. Dewpoints remain fairly high near 15 at the noon hour. CAPE is relatively low today given the setup - so severe hazards are not forecast. Tomorrow is a different story across NB. The freezing levels will be much lower creating a possible hail-favoured setup. Additionally, if organized cells do form, they will bring an inherent wind risk. G90 are possible and are depicted by the yellow hazard area. This severe weather risk will be re-analyzed and potentially alerted for on Wednesday.

Thunderstorm Outlook for Today

Thunderstorm Outlook for Tonight

Thunderstorm Outlook for Tomorrow

Forecaster: Tirone.

Convective Outlook Valid for Today, Tonight and Tomorrow

Regional Impacts

Today

NB: Chance of some scattered thundershowers over western New Brunswick this afternoon with some locally heavy downpours.

Lab: Chance of some isolated thundershowers through central Labrador this afternoon.

NS/PEI/NFLD: None.

Tonight

NS/NB/PEI/NFLD/LAB : None.

Tomorrow

LAB: Risk of some marginally severe thunderstorms over southern Labrador in the afternoon with small hail, strong wind gusts, and locally heavy downpours.

NS: Risk of an elevated thundershower over southern mainland Nova Scotia through the day.

NB/PEI/NFLD: None.

 

Convective Discussion…

A ridge of high pressure sits over central Atlantic Canda this morning with a weak surface trough extending from central Maine up into central Quebec, just west of Labrador. This trough will be the main focus for any convection today, as it slowly begins to move east. A small but strong upper low over central Ontario will combine with a shortwave near New England and approach the trough this afternoon, which will act as the main trigger for convection. MLCAPE values over western New Brunswick are forecast to be around 500 to 750 J/kg today, with effective shear around 15 to 25 knots. One of the limiting factors however is how quickly the shortwave is advected East into New Brunswick, as well as some warm air aloft between 500 and 700 mb. This could limit the higher shear and some better thermodynamics from reaching the risk area until later this evening, which would lead to more isolated and short-lived thundershowers this afternoon. The risk for more organized storms could still increase into this evening however as the shortwave approaches, which could be capable of producing some locally heavy downpours of 10 to 20 mm per hour.

There is also a slight risk of some isolated thundershowers with a weak trough over central Labrador today which is in a similar environment to western New Brunswick, however there is a lack of moisture evident over this area which will reduce the risk of storms here today. Current surface observations show dewpoints only in the 5 to 7 degree range, with temperatures already above 20. Nonetheless, the potential for some isolated thundershowers exists which could produce some gusty winds.

Tonight, the shortwave will reach the Gulf of Maine, bringing with it the risk of an elevated thundershower over the marine areas west of Nova Scotia in the early morning hours. Into tomorrow, the shortwave will track across Nova Scotia, continuing to bring the chance for an elevated thundershower across the southern half of the mainland during the day and into the evening. Elsewhere, the upper low currently over central Ontario will sit over central Quebec by tomorrow morning with today’s surface trough now extending east from the upper low into southern Labrador. This will be the main focus for convection tomorrow, as MLCAPE values in the warm sector just south of the trough could reach 750 to 1000 J/kg by the afternoon. Slightly better moisture being advected in from the south and effective shear in the range of 20 to 30 knots should be sufficient to get some organized, marginally severe thunderstorms tomorrow afternoon. The surface trough is initially forecast to remain fairly stationary before eventually shifting south in the late afternoon/early evening. This in combination with an expected easterly storm motion could lead to some multi-cell training storms early in the day which would increase the risk of heavy rainfall for some areas. Some small hail and strong wind gusts are also possible with these storms. Luckily, the main risk area is expected to remain over unpopulated areas but could impact a few communities early in the afternoon.

 

Thunderstorm Outlook for Today

Thunderstorm Outlook for Tonight

Thunderstorm Outlook for Tomorrow

Forecaster: Copp

Convective Outlook Valid for Today , Tonight and Tomorrow

Regional Impacts

NS… Chance of thunderstorms today, some heavy downpours possible.

NB.. Chance of thunderstorms today and tomorrow. Heavy downpours possible with small hail.

PEI.. No thunderstorms expected.

Newfoundland.. No thunderstorms expected.

Labrador.. Low chance of thunderstorms expected tomorrow.

Convective Discussion

Instability will persist over western areas today as an upper trough slowly exits the region. CAPE values are expected to remain modest, reaching around 1000 J/kg, with generally weak low-level shear and deep-layer shear staying below 25 knots across most of New Brunswick.

As a result, severe thunderstorms are unlikely. However, isolated cells may still produce small hail and locally heavy downpours.

Looking ahead to tomorrow, shear will increase somewhat, but the relatively cool airmass will limit the available energy for convection. Non-severe showers or thunderstorms may once again develop over western areas. With limited heating and only modest increases in dew points expected in the coming days, overall conditions are not anticipated to change significantly.

Thunderstorm Outlook for Today

Thunderstorm Outlook for Tonight

Thunderstorm Outlook for Tomorrow