Convective Outlook Valid for Today , Tonight and Tomorrow

Regional Impacts…

 

Today

NB/NS/PEI:  A chance of severe thunderstorms bringing heavy rain, hail and strong wind gusts.

NL/Labrador: None.

 

Tonight

NB/NS/PEI/NL/Labrador: None

 

Wednesday

NB/NS/PEI/NL/Labrador: None

 

 

Convective Discussion

Low-level moisture advection continues this morning ahead of a cold front which will move across northern New Brunswick this afternoon and into southern New Brunswick this evening.  Dew point temperatures in the low 20s are occurring throughout most of the Maritimes. The combination of this warm, moist airmass and the approaching cold front should be sufficient to trigger severe weather across portions of New Brunswick, Nova Scotia and Prince Edward island this afternoon and into the evening. CAPE values of 1000-2000 J/kg and precipitable water values of up to 50 mm could produce very high rainfall rates in thunderstorms. Additionally, relatively dry mid levels and a low level jet near 30 knots will allow strong downdraft potential to exist. Effective shear of 30 to 40 knots means that some supercell storms could develop, leading to potentially damaging wind gusts. After the frontal passes tonight, quiet weather will return for a few days.

Thunderstorm Outlook for Today

Thunderstorm Outlook for Tonight

Thunderstorm Outlook for Tomorrow

Convective Outlook Valid for Today , Tonight and Tomorrow

Regional Impacts

NB… No impacts expected today. Some thunderstorms tonight and overnight bringing frequent lightning and possibly heavy downpours. Tomorrow… Some severe thunderstorms bringing heavy rain and potentially strong wind gusts.

PEI… No impacts expected today. Some thunderstorms overnight bringing lightning and possibly some heavier rainfall. Tomorrow… Thunderstorms possible with gusty winds and possibly heavy downpours.

NS… No impacts expected today. Some thunderstorms overnight over north areas, bringing lightning and possibly some heavier rainfall. Tomorrow… Thunderstorms possible with gusty winds and possibly heavy downpours for central and eastern regions.

NFLD… No Impacts today… Tomorrow… A chance of thunderstorms over western parts of the island tomorrow with some heavier rain possible.

Convective Discussion

For the most part, thunderstorm activity will remain upstream over Quebec and Ontario today, as a low-pressure system and its associated cold front gradually move eastward. An area of high pressure to the southwest will likely help suppress thunderstorms over the Atlantic region until the unstable airmass reaches the Maritimes tonight.

We will continue to see low-level moisture advection ahead of the approaching cold front today and overnight, with dew point temperatures likely reaching the low 20s in some areas by tomorrow. The combination of this warm, moist airmass and the surface low-pressure system will be sufficient to generate CAPE values around 2000 J/kg. With precipitable water values near 50 mm, rainfall rates in thunderstorms are likely to be very high. Additionally, strong downdraft potential exists, and it is possible that some supercell storms could develop, leading to potentially damaging wind gusts.

The timing of the cold front’s passage may prove critical; if it arrives earlier than expected, the threat of severe weather may shift somewhat eastward. Thunderstorm development over Quebec today will give us a general idea of what to expect tomorrow for New Brunswick. However, as is often the case, these systems do not always unfold as predicted, and timing may shift. Keep an eye out for alerts, not just for tomorrow but also overnight, as the system approaches.

Thunderstorm Outlook for Today

Thunderstorm Outlook for Tonight/Overnight

Thunderstorm Outlook for Tomorrow

Convective Outlook Valid for Today, Tonight, Tomorrow and Tuesday

Regional Impacts

Today:

NS: Risk of embedded thundershowers early this afternoon with locally heavy downpours.

Tonight:

None.

Tomorrow:

None.

Tuesday:

NB/PEI: Risk of severe thunderstorms with locally heavy rainfall, small hail and strong wind gusts.

NS /NL: Risk of thundershowers giving local heavy downpours and strong wind gusts.

Convective Discussion

A short-wave trough is moving through the Maritimes today. Based off the 12Z Caribou sounding, the 500 mb temperatures would suggest that convection will remain capped as the rain moves through, although the band has produced some 10-15 mm/hr rainfall rates over northwestern New Brunswick this morning as precipitable water is in the mid 30s.  These heavier showers are expected to diminish by the time the band moves into eastern Nova Scotia as the wave buts against the ridge of high pressure over Newfoundland. There have been a few strikes over the western Maritime marine waters this morning and the small threat of embedded thundershowers may continue into western Nova Scotia early this afternoon where they may be enough lift between 700 and 850mb to break the cap.  A cold front will move southeastward across Labrador this afternoon and evening, but the 500 mb temperatures also will be a limiting factor in any convection that develops.

For tomorrow, the weakened trough keeps Newfoundland under cloud and showers for most of the day, while the Maritimes most of Labrador are under a ridge of high pressure. This ridge extends across most of the eastern US, with building heat and humidity into New Brunswick. A low pressure system over central Ontario moves into Central Quebec in the evening. An area of destabilization will move towards the Gaspe Peninsula and into northern New Brunswick later in the evening with the risk of a thunderstorm lingering into the overnight but given the timing, the risk of anything severe is limited.

For Tuesday, there is increasing heat and humidity for all the Maritimes with dewpoints into the low 20s.  A cold front is expected to track across New Brunswick in the afternoon. The high surface temperatures combined with cooling in the mid-levels with the cold front along with decent CAPE and wind shear, will provide the potential for severe thunderstorms mainly for New Brunswick and Prince Edward Island. Details will become more clear in the coming day.  

Thunderstorm Outlook for TODAY

Thunderstorm Outlook for TONIGHT

Thunderstorm Outlook for TOMORROW

Thunderstorm Outlook for TUESDAY

 

Roberta McArthur

 

 

Convective Outlook Valid for Today, Tonight and Tomorrow

Regional Impacts

Today:

Lab: Slight risk of a thundershower.

Maritimes/NL: None

Tonight:

None.

Tomorrow:

None.

Convective Discussion

A low pressure system will continue to move eastward across the Northeastern Gulf into the Labrador Sea today. There is not much support remaining for convection with this low  other than north of the low in an easterly flow aided by the lift from the higher terrain in Eagle River forecast region which has sparked some thundershowers this morning and may persist into the early afternoon. There is also a slight risk remaining along the cold front over the southwestern Grand Banks.

Behind the low there is a ridge of high pressure that will dominate the Maritimes and western Labrador today, suppressing convection. Tonight, an active short-wave will bring rain through the Maritimes on Sunday but the convective threat is limited as the mid level are too warm. A cold front will push through Labrador tomorrow afternoon bringing showers but the mid-level temperatures also appear to warm to allow convection.

Thunderstorm Outlook for TODAY

Thunderstorm Outlook for TONIGHT

Thunderstorm Outlook for TOMORROW

 

Roberta McArthur

 

 

Convective Outlook Valid for Today, Tonight and Tomorrow

Regional Impacts

Today:

NB: Chance of thunderstorms giving locally heavy rain and strong wind gusts.

NL: Slight risk on a thundershower over the northern Peninsula

NS/PEI/Labrador: None.

Tonight:

NB/Gulf waters: Chance of embedded thunderstorms.

NS/PEI/NL/Labrador: None.

 

Tomorrow:

None.

Convective Discussion

A deep upper trough over central Quebec with a surface low pressure system currently over northwestern New Brunswick with track eastward today across the northern Gulf of St. Lawrence and into the Labrador Sea tomorrow. Embedded thunderstorms have moved across northwestern New Brunswick this morning ahead of the low, and further convection may fire along the cold front, which will move across New Brunswick this afternoon and evening. Meanwhile, along the warm front there has been isolated strikes across northern Newfoundland and the risk will continue into the early afternoon. The air mass in the warm sector is quite humid with dew points exceeding 20C. With a stalled ridge across northern Quebec into Labrador, ahead of the low, rainfall amounts are expected to reach upwards of 70 mm.

Along the cold front, thunderstorms will trigger this afternoon into the evening across New Brunswick into the Gulf waters with heavy rainfall being the biggest threat with precipitable water reaching 45 mm. Mixed CAPE values across northern New Brunswick may reach 500 J/kg if we get some clearing, and with effective shear of 30 to 40 kt, some organization is possible into line segments capable of producing strong wind gusts.  Storms will move fairly quickly towards the northeast under a 40 kt 700 mb flow.  Some overnight convection may hold across eastern New Brunswick and over the Gulf before the threat weakens overnight and into tomorrow.

Tomorrow the low continues eastward into the Labrador Sea and a ridge moves into the Maritimes with no thunderstorms are expected at this time.   

Thunderstorm Outlook for TODAY

Thunderstorm Outlook for TONIGHT

Thunderstorm Outlook for TOMORROW

 

 

Roberta McArthur