Convective Outlook Valid for Today , Tonight and Tomorrow

Regional Impacts:

 

Today

NB/NS/PEI/NL/Labrador: None

 

Tonight

NS/NB: Thundershowers giving local downpours.

PEI/NL/Labrador: None.

 

Wednesday

NS/NB/PEI/NL: Thundershowers giving local downpours.

Labrador: None

 

Convective Discussion:

A low approaching from the Great Lakes area will track across the region on Wednesday. There are already rainfall warnings in effect for areas of New Brunswick and they will be expanded to the southwest and issued for areas of central and western Nova Scotia. No surface based convection is expected however the mid level instability ahead of the low is quite significant and is represented in very low Showalter indices.  Gusty winds up to 60 km/h are possible. PWAT values of 40-50 mm enhance the downpour threat and that is evident in observations currently coming out of areas of New England where 25 mm/hr or higher have been reported.

 

Thunderstorm outlook for today:

 

Thunderstorm Outlook for Tonight:

 

Thunderstorm Outlook for Tomorrow:

Convective Outlook Valid for Today , Tonight and Tomorrow

Regional Impacts

 

Today

NB/PEI/Les Iles/NS: none

NL&LAB: showers exiting the province

 

Tuesday

NB/NS: A few embedded thunderstorms late in the day in warm air advection over western regions.

PEI/Les Iles: none

NL&LAB: Risk of a thunderstorm over northern and central portions of Labrador

 

Convective Discussion

The upper low has moved east of NF this morning, and the associated residual shower activity will taper off during the day. An upper ridge is building over the Maritimes, however as the diurnal instability increases cumulus field will develop across the region. Cloud top between 2-4 km with maximum of 5 km can be expected.

On Tuesday, bands of thunderstorms from New England/Gulf of Maine will be advancing in the warm advection over the Maritimes late in the day. To a lesser extent warm air advection will also promote some thunderstorm activity over northern Que, possibly reaching Labrador. Instability will not be the greatest but this moisture-rich airmass will bring surface dewpoints to 18-20, and at the end of the day, a swath of moisture with precip water of 40-50 mm will extend from Browns bank/Lurcher to the St. Lawrence valley. The main forecast models show a surface low moving across eastern Ont/southern Que Tuesday, and then over NB and Gulf of St. Lawrence Wednesday. At this time, an average of the precipitation guidance would suggest totals of 50-80 mm with the maximum amounts over the lower St. Lawrence/Gaspé/northern NB. These numbers are preliminary for the large scale and could be augmented if smaller embedded/elevated convective features become more predominant.

 

 

Thunderstorm Outlook for Today

 

Thunderstorm Outlook for Tonight

 

Thunderstorm Outlook for Tomorrow

Convective Outlook Valid for Today , Tonight and Tomorrow

Regional Impacts

 

Today

NB/PEI/Les Iles: Isolated thunderstorms giving heavy downpours and gusts near 50 km/h

NS: Scattered thunderstorms over eastern half of the province giving localised heavy downpours, small hail and wind gusts near 70 km/h.

NL&LAB: None

 

Convective Discussion

An upper low high pressure near the Gaspe peninsula will slowly advance eastward today and tonight, at the surface there are two areas of rain associated with a couple of low pressure systems, one near Anticosti island and a second one south of the Burin peninsula. NF radar estimates for the past 12 hours suggest rainfall amounts of 20 to 40 mm with the highest amounts just off the west coast and south of the burin, however observations from autostations suggests amounts of 10 mm. There will likely be another 10-20 mm to come until tomorrow.

The focus for surface-based convection this afternoon will be over the NErn half of NB, PE, and especially Ern NS. Under a cold pool (-16) associated with the upper low, the cumulus field is already starting to grow and diurnal instability will be on the increase during the afternoon. Surface temperature of 24 or 25 will likely be plenty to bump MLCAPE values to nearly 500 J/kg / LI of -2. There are some interesting upper dynamics combining with these conditions, including 500 mb positive vorticity advection and a slightly cyclonic 80 knots upper jet branch south of NS, placing CB and Cabot strait near a right exit. The Shearwater Hodograph shows about 30 knots of effective deep layer shear. Eastern-most areas of NS mainland and Srn CB could get stronger thunderstorms that could evolve into longer-lasting linear features and produce downpours/small hail/high winds.

A high pressure system will build in from the west tonight and Monday.

 

 

Thunderstorm Outlook for Today

 

 

Thunderstorm Outlook for Tonight

 

Thunderstorm Outlook for Monday

 

 

 

 

 

Convective Outlook Valid for Today, Tonight and Tomorrow

Regional Impacts

 

Today

NS/PEI: Isolated embedded thunderstorms giving lightning, heavy downpours with up to 50 mm/h rates and strong wind gusts

NB: Isolated embedded thunderstorms giving lightning, heavy downpours, small hail and strong wind gusts

NL&LAB: None

 

Tonight

NS: Isolated embedded thunderstorms giving lightning, heavy downpours and strong wind gusts over Cape Breton

NL: Isolated embedded thunderstorms giving lightning and heavy downpours.

 

Sunday

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

 

 

Convective Discussion

 

A warm and moist air mass continues to spread north and eastward across the Maritimes today ahead of a trough from a quasi-stationary low over central Quebec. The trough becomes oriented northwest/southeast today as the low centre slowly shifts southeastward across the Gulf of St. Lawrence and south of Newfoundland Sunday night. A thin stream of 40-50 mm precipitable water values is being fed northward across Nova Scotia, allowing for very high rainfall rates where 50 mm/h has been seen in parts of the HRM this morning with training thunderstorms. Areas of upper level rotation have also been evident with some wind gusts reaching 60 km/h in the stronger cells. Although lightning activity has diminished, the heavier band continues slowly north and eastward today, exiting east of Cape Breton tonight and the threat of heavy rainfall continues. A increasingly heavier rain band over southeastern New Brunswick will give high rainfall rates today which will affect parts of northern Nova Scotia and Prince Edward Island this afternoon and evening.

 

With expected clearing behind the trough today over western New Brunswick, convection is possible in the afternoon and late evening. With an increase in CAPE values exceeding 1000 J/kg, lower freezing levels, and weak to moderate 0-6km shear, there is the threat for small hail, strong wind gusts and locally heavy downpours.

 

There is the risk of waterspouts tonight into Sunday morning mainly in the Northumberland Strait and southern Gulf of St. Lawrence, where the highest SST’s above 20C and cooler 850mb temps are located, along with weak to moderate deep shear.

 

On Sunday, convection is possible again for the Maritimes in the afternoon still under the influence of the upper low which will move east of Newfoundland by Monday. With cooler air aloft, CAPE values approaching 1000 J/kg and weak to moderate shear of 20-30Kt, there is the threat of pulse or multicells over central and eastern New Brunswick towards Prince Edward Island and northern Nova Scotia.

 

Thunderstorm Outlook for Today

 

Thunderstorm Outlook for Tonight

 

Thunderstorm Outlook for Sunday

Convective Outlook Valid for Today, Tonight and Tomorrow

Regional Impacts

 

Today

NB: Isolated thunderstorms for northwestern regions this evening bringing lightning and locally heavy downpours

NS/PEI/NL&LAB: None

 

Tonight

NB/NS/PEI: Isolated embedded thunderstorms bringing lightning and heavy downpours

NL&LAB: None

 

Saturday

NB: Isolated embedded thunderstorms bringing lightning, heavy downpours, small hail and strong wind gusts

NS/PEI: Isolated embedded thunderstorms bringing lightning and heavy downpours

NL&LAB: None

 

 

Convective Discussion

 

With a near quasi-stationary low pressure centre over central Quebec, an associated trough will slowly track through southern Quebec and into Maine and western New Brunswick today. Showers and isolated thundershowers ahead of this feature have been ongoing this morning over northwestern New Brunswick. Although more favourable dynamics remains further west over New England today, increasing precipitable water into the mid 30s and mean storm motion to the northeast with 0-6km shear of 30 KT, could make for sustained convection and locally heavy rainfall due to possible training of storms over the same area. The trough will bring showers and embedded thunderstorms slowly eastward tonight and into Saturday across the Maritimes. There is also a waterspout risk over the Gulf of St. Lawrence and southern Maritime waters Saturday into Sunday with a 10 deg temperature difference between 850mb and surface SST’s, deep convective cloud depths above 35,000ft and little directional shear.

 

 

Thunderstorm Outlook for Today

 

Thunderstorm Outlook for Tonight

 

Thunderstorm Outlook for Saturday