Convective Outlook Valid for Today and Tomorrow

Regional Impacts:

 

Today

Northwestern NB: isolated lightning, locally heavy downpours and gusty winds

PEI/NS/NL/Labrador: None

 

Tonight

Western NB/NS: Isolated lighting and locally heavy downpours

 

Tuesday

NB/NS: isolated lightning and locally heavy downpours

PEI/NL/Labrador: None

 

Convective Discussion:

 

A low pressure system will advance northeastward over Hudson Bay with a trough extending southward into New England today. There is a risk for convection over northwestern New Brunswick ahead of the trough and will continue eastward into the evening. The limiting factor is a warm nose at 850 mb and 500 mb as seen on the 12Z KCAR sounding. However, should daytime surface temperatures reach 30 degrees, along with the thermal trough at 500 mb pushing eastward, it should be enough to initiate convection over central Maine this afternoon. With increasing 0-6km shear and precipitable water above 40 mm, more organized lines that develop could maintain into New Brunswick into the evening.

 

An isolated TCU is possible over northeastern New Brunswick as well but there may be too much warming aloft to initiate any CBs.

 

As the trough continues to approach overnight and into Wednesday, convection will be more elevated and isolated in nature. A short wave will develop south of Long Island this evening and get wrapped into the main trough as it tracks through the Maritimes. This moisture will get drawn northeastward towards western Nova Scotia early Wednesday morning and continue through the Maritimes and towards southern Labrador by Thursday morning. The main threat will be locally heavy downpours with precipitable water values near 50 mm along the Atlantic coast of Nova Scotia.

 

Thunderstorm outlook for today:

 

Thunderstorm outlook for tonight:

 

Thunderstorm outlook for Wednesday:

Convective Outlook Valid for Today and Tomorrow

Regional Impacts:

 

Today

Labrador: Isolated lightning and locally heavy downpours

NB/PEI/NS/NL: None

 

Tonight

None

 

Tuesday

NB: Isolated lightning and locally heavy downpours over northern sections

PEI/NS/NL/Labrador: None

 

Convective Discussion:

 

An elongated quasi-stationary front rides from Hudson Bay across central/northern Quebec and across central Labrador. Convection will be isolated and embedded in nature along this feature as the atmospheric profiles are moist adiabatic, but with some slight cooling at 700 mb and lower level jets at 850 mb and 700 mb to help provide lift over the higher terrain. With CAPE values of 200-300 J/kg, weak to moderate effective shear and precipitable water in the 30 to 40 mm range, locally heavy downpours will be the biggest impact.

 

A low pressure system will advance northeastward over Hudson Bay with a trough extending southward into New England on Tuesday. There is a risk for convection over northwestern New Brunswick for tomorrow ahead of the trough. A sea-breeze set up combined with surface-based heating over the Acadian Peninsula may also provide enough lift to push past a warm nose between 700 and 500 mb in order to produce isolated convection in the afternoon.

 

Thunderstorm outlook for today:

 

Thunderstorm outlook for tonight:

 

Thunderstorm outlook for Tuesday:

 

Convective Outlook Valid for Today and Tomorrow

Regional Impacts:

 

Today

NS: isolated lightning

NB: none

PEI: none

Labrador: none

NL: isolated lightning

 

Tonight

None

 

Sunday:

NS: none.

NB: none.

PEI: none.

Labrador: isolated lightning

NL: none.

 

Convective Discussion:

A decaying cold front could act as a trigger for a few isolated CBs later today, especially where surface convergence will be enhanced by S-SW flow off the Atlantic. Instability appears sufficient with MLCAPEs ranging from 300-500 J/kg, however skinny CAPE profiles and dry entrainment above 650 mb could act to limit updraft strengths in the IC growth zone for sufficient charge separation. A similar scenario appears likely in eastern NL however it appears dry air entrainment does not appear to be as much of a limiting factor, despite skinny CAPE profiles. Effective shears of 20-30 kts in NL appear more reasonable given the instability as opposed to NS where shear might be too strong for the available instability (effective shears of 30-40 kts).

 

Tomorrow appears rather quiet, western Labrador may see some elevated convection with as a shortwave from northern MB moves eastward along a zonal Baroclinic zone.

 

Thunderstorm outlook for today:

 

 

Thunderstorm outlook for Sunday:

 

 

Convective Outlook Valid for Today and Tomorrow

Thunderstorm Outlook valid for TODAY – FRIDAY, Aug 26^th:

 

Regional Impacts

Scattered thunderstorms are expected to enter into NB this afternoon along an approaching frontal feature. Moderate rain is expected, and wind gusts near 80km/h are possible. Pockets of stronger severe weather are possible IF the dynamics align favourably with storm motion and the overhead jet support. A squall line/bow echo signature cannot be completely ruled out with this feature. If ingredients build, a watch will be used to achieve lead time for residents of NB.

 

Convective Discussion

The aforementioned frontal feature is digging quite deep as it comes through upstate NY, New Hampshire and Vermont at this hour. This is the main forcing of the day for NB. With surface moisture pooling ahead of the front (Pwats over 30mm), and 0-6k shear values near 35kTs, thunderstorms are forecast to develop this afternoon and evening. Morning soundings across the Maritimes show quite a dry level above 700mb, but this will saturate as the day progresses. A challenge does remain with the existing junky cloud, but clearing is expected to occur at the prime time for peak insolation. The HRRR solution remains as an outlier, bringing a very strong bow echo signature through Maine and all the way to Bathurst this evening. The probability of this particular scenario remains low at this time, but forecasters are closely monitoring upstream data to alert to a strong signature should it develop. In this case, the yellow hazard area for wind may be underdone for max gusts. (A stationary boundary is also offshore still producing ongoing lightning and shower activity on the southern Grand Banks of the marine district.)

 

TODAY

 

Thunderstorm Outlook valid for TOMORROW – SATURDAY, Aug 27^th:

 

Thundershowers are expected to continue through the overnight hours and affect areas in Nova Scotia early Saturday morning. These partially elevated storms will likely bring bouts of showery weather and lightning. Mainland NS will clear out by noon at the latest. Late day weekend events do not need to be rescheduled due to svr weather. Nfld can expect the same thundershowers and dynamics in the afternoon, near Gander. Lightning will be the main hazard with any cell that does develop.

 

TOMORROW

 

Forecaster: TIRONE/ASPC

Convective Outlook Valid for Today and Tomorrow

Regional Impacts:

 

Today

NS: isolated lightning

NB: none

PEI: isolated lightning

Labrador: isolated lightning

NL: none

 

Tonight

None

 

Friday:

NS: none.

NB: moderate-high rainfall rates, gusty winds, small hail and lightning.

PEI: moderate rainfall rates, and lightning.

Labrador: isolated lightning

NL: none

 

Convective Discussion:

A weakening cold front moving through the southern Maritimes may trigger a few thunderstorms this afternoon in eastern NS and PEI. Instability will be limited by dry air intrusion, with profiles quite dry above 720mb. Dynamics look less impressive than yesterday with shear near 20 kts at most. Regardless with a convective temperature of 26, MLCAPE near 700 J/kg may be realized. Further north in southern Labrador elevated convection associated with a vigorous upper trough may continue to produce some isolated lightning. Cloud cover looks too extensive to allow surface based convection.

 

Tomorrow an upper trough from northern Ontario is expected to move through southwestern new England during peak insolation bringing a risk for severe storms there. In New Brunswick the situation becomes a little tricky as moisture advection ahead of the trough will begin to destabilize southwestern sections of the province in the afternoon; increasing the risk for higher rainfall rates in any storms that do develop. However it appears the best Dynamics, and lift associated with the upper trough itself will remain to the southwest over Maine during peak insolation. It is possible that early evening storms remain surfaced based upon crossing the boarder, which would bring a wind and hail hazard to go with the higher rainfall rates. Storm motion will initially be 20 to 30 kts out of the SW, but increase as dynamics improve later in the day (perhaps as high as 40 kts by 0z Saturday). Later in the evening it is expected storms will maintain a moderate rainfall hazard as they become elevated and move into eastern sections of NB and westernmost PEI.  

 

Thunderstorm outlook for today:

 

Thunderstorm outlook for tonight:

 

Thunderstorm outlook for Friday: