Convective Outlook Valid for Today and Tomorrow

Thunderstorm Outlook for Day 1

 

Regional Impacts

New Brunswick and western Nova Scotia: Depending on cloudiness, possibility of thunderstorms east and severe thunderstorms west, with heavy downpours the greatest threat, followed by gusty winds.

Northern Newfoundland and southeastern  Labrador: chance for non severe thunderstorms,

 

 

Convective Discussion

The synoptic situation is similar to yesterday, with a low near Hudson Bay and a second over the Labrador Sea, with an extended east-west trough between them and over Labrador. This also produces slight ridging over Quebec and New England.  For Newfoundland and Labrador there is some support for non-severe convection near the Strait of Belle Isle.  Some weak PVA from a jet right exit, combined with daytime heating may give a few cells. PWAT is only about 20 mm., but CAPEs in excess of 200 J/kg with a slight chance of 500 J/kg are possible.  Gusty winds and brief heavy showers are the main issues, with a slight chance for hail with YYR having freezing levels below 8000 ft.

 

For the Maritimes things are trickier. Cloudiness will be the key. There’s some upper support from a 500 mb jet near southwestern New Brunswick with some associated lift, with plenty of moisture below 700 mb. PWATs range from 40-60 mm, with surface dewpoints near 20 C,  and 850 dewpoints up to 15 C , with a moist tongue poking into southern New Brunswick. If things clear, CAPEs of up to 1000 J/kg or maybe higher are possible. Freezing levels near 15,0000 ft suggest large hail is unlikely. Very heavy rainfall is the largest risk, followed by gusty winds that may reach warning level, and finally some small hail. For the rest of New Brunswick and parts of Nova Scotia, the impacts will be somewhat weaker, but rainfall followed by winds as the main risks.

 

 

Thunderstorm Outlook for Day 2

 

Convective Outlook Valid for Today and Tomorrow

Thunderstorm Outlook for Day 1

 

Regional Impacts

New Brunswick: Possibility of non-severe thundershowers in the northeast if the thick cloud there burns off this afternoon. Possibility of Severe thundertorms in the extreme southwest if the cloud deck moves away or burns off,  with high wind the largest risk, followed by heavy downpours.  

Newfoundland: thunderstorms beginning this afternoon with possible heavy downpours, especially with the slow movement of the cells.

 

Convective Discussion

 

For Newfoundland: there’s a low of the coast of Labrador  from 250 mb down, with some upper dynamic support with PVA approaching western Newfoundland.  There’s some good moisture with dewpoints of up to 17 C and PWATs near 24 mm, with most of it below 850 mb, Shear and storm motion is relatively low,  suggesting plenty of time for rain to accumulate, and mean layer CAPEs suggest possibly reaching or exceeding 500 J/kg near and west of Gander, if they can get some clearing. Small hail is also possible, with freezing levels around 10-11,000 ft.

 

For New Brunswick:  there are some good ingredients, especially in the far southwest, but the big inhibitor is cloudiness.  The most likely place for convection is in the northeast, where things may start clearing this afternoon, but with non-severe cells likely. The general ingredients are near 50 kts of shear, PWATs in the 30-45 mm range, with surface dewpoints near 19 C and 850 dewpoints near 13 C moving in from the west.  If things clear in the north, CAPEs could reach 200-500 J/kg.  Gusty winds and local heavy downpours are the main threats, but the cells should move fast enough to limit therainfall from any given cell.

 

For the southwest the main risk would be wind gusts possibly reaching warning level, followed by local heavy downpours. Again, this is assuming some surface insolation this afternoon.

 

 

Thunderstorm Outlook for Day 2

 

Convective Outlook Valid for Today and Tomorrow

Regional Impacts

Maritimes – Heavy rainfall with small hail and strong gusts with the strongest likelihood along coastal NS but eastern inland NS and eastern NB also possible.

Newfoundland and Labrador – risk of thundershowers with slight chance of severe over central and northeast.

 

Convective Discussion

Potential for thunderstorms today for some regions.  Upper dynamics will become favourable for tstorm formation today as the Maritimes enters the left exit area of an upper jet and area of diffluence.   Cooling aloft through the first part of the day will help destabilize the upper atmosphere.  Closer to the surface, there is quite a bit of moisture at the surface but it does not extend significantly up to 850mb.  There is some higher moisture values moving in today but again…not significantly high.  Precipitable water values of around 25 to 30 mm are expected.  0-6 km shear values as high as 35 kts so this will be enough to maintain tstorms if/when they form.  500 to 1000 J/kg of CAPE can be expected today for the Maritimes.  The one thing that seems to be lacking is a significant synoptic feature to kickstart tstorms.  What we will have is coastal convergence along sea breeze fronts that are expected to develop this afternoon.  That will be the main area of concern but inland areas could get tstorms if there are some weak areas of convergeance in the area or if coastal storms advect.  The highest impact would be heavy rainfall as storms along the coast will likely be moving slowly and/or training could develop. Newfoundland is farther from the favourable dynamics today but still have a risk of thunderstorms especially over central and northeast.

 

Thunderstorm Outlook for Day 1

 

Thunderstorm Outlook for Day 2

 

Barrie MacKinnon

 

Convective Outlook Valid for Today and Tomorrow

Regional Impacts

Southeastern Labrador could experience strong thunderstorms this afternoon - the main threat is damaging wind gust, brief downpours and small hail – into the evening.

 

Convective Discussion

This morning, a frontal wave was located south of Newfoundland. The elongated front has an history of producing locally heavy rain as far back as NB (reports of rainfall rates of 20-40 mm). Earlier lightning activity has faded during the past two hours. This feature will continue to move eastward – out of the region - throughout the afternoon.

The main are of focus for the afternoon is Labrador where an upper cold low prevails. The cold pool would be sufficient to trigger isolated thunderstorms, but this likelihood will be enhanced by an approaching vorticity rotating around the low. The moisture available in this airmass is not tremendous, but the energy available is high enough to anticipated the development of fairly robust eastward moving storms capable of producing small hail, damaging wind gusts and localised downpours.

 

 

Thunderstorm Outlook for Day 1

 

 

 

Thunderstorm Outlook for Day 2

 

 

Convective Outlook Valid for Today and Tomorrow

Regional Impacts

Strong clusters of thunderstorms could produce localized heavy downpours early this afternoon over southwestern Nova Scotia.

Later this afternoon, thunderstorms formation over central and southern Maine could spread robust clusters over southwestern New Brunswick, the main threat would be brief heavy rain and damaging wind gusts.

 

Convective Discussion

 

An upper trough along with a weak cyclonic upper jet over northern Quebec could trigger an isolated thunderstorm over western Lab, in the east Goose is showing stability in the mid-levels so convection will be limited to fair weather cumulus. For the Maritimes, two distinct air mass present different threat. For Nova Scotia a surface front extends from the New England coast to Northumberland Strait, a southwesterly low-level jet is feeding moisture over the area with moderate to heavy rain expected at times. For New Brunswick, a surface feature to the west will provide the forcing necessary for thunderstorm initiation over the Maine Highlands. A 100kt upper level jet could help sustain these individual storms long enough for them to propagate eastward into western NB.  Although the main threat with these storms would be brief downpours and damaging wind gusts - none of the severity indicators are particularly high at this point.

 

Thunderstorm Outlook for Day 1

 

 

 

Thunderstorm Outlook for Day 2