Convective Outlook Valid for Today, Tonight and Tomorrow

Regional Impacts

Today: Some scattered thunderstorms possible across Atlantic Canada today. Main hazards are locally heavy downpours, small hail, and some strong wind gusts.

Tonight: Risk of some isolated thundershowers tonight through the central Maritimes. Locally heavy downpours are the main hazard.

Tomorrow: Some scattered thunderstorms possible over central Newfoundland tomorrow afternoon. Main hazards are locally heavy downpours, small hail, and some strong wind gusts.

Convective Discussion…

A cold front that moved through New Brunswick yesterday continues to produce some thunderstorm activity over the Gulf of St. Lawrence and eastern PEI this morning. Bulk shear values over 40 knots here under the 500 mb jet will aid in sustaining these storms through the day with land impacts likely to only be felt in the Magdalen Islands and northern Cape Breton early this afternoon, and extreme western Newfoundland later this evening. Heavy downpours are the main risk with these storms due to some higher PWAT values over 35 mm here, though some small hail is also possible with the strongest cells.

In addition, an upper low centred over northern Maine this morning will track into southern New Brunswick early this afternoon and continue to move east through the day. Modest MLCAPE values of 500 to 1000 J/kg through southern New Brunswick and central/eastern Nova Scotia will support the development of some thunderstorms out ahead of the upper low, in areas of enhanced vorticity advection. Bulk shear values are a bit lower than yesterday here, in the 25 to 35 kt range, which should limit storms from becoming severe or very long-lived. PWAT values in the 20 to 30 mm range and low freezing levels hint at the risk for some locally heavy downpours and small hail. Some of these storms may sustain themselves overnight around the upper low centre as it moves through the central Maritimes. Tomorrow, a similar environment is in place for central Newfoundland with the same upper low forcing convection.

Thunderstorm Outlook for Today

Thunderstorm Outlook for Tonight

Thunderstorm Outlook for Tomorrow

Forecaster: Copp

Convective Outlook Valid for Today, Tonight and Tomorrow

Regional Impacts

Today: Organized strong to severe thunderstorms across much of New Brunswick this afternoon. Main hazards are strong wind gusts, large hail, and heavy downpours. Also the chance for some isolated thundershowers over central Newfoundland.

Tonight: Elevated thundershowers with locally heavy downpours possible over central Atlantic Canada tonight.

Tomorrow: Risk of scattered thundershowers with some strong wind gusts and locally heavy downpours over central Atlantic Canada tomorrow.

Convective Discussion…

A potent day is in store for much of New Brunswick today as an upper low spins into the region. A very unstable airmass in combination with an approaching cold front has triggered some strong to severe thunderstorms this morning along the St. Lawrence river valley. This front will move east, reaching western New Brunswick early this afternoon. The 12Z Caribou sounding from this morning indicated the potential for upwards of 2000 J/kg of MLCAPE given sufficient surface heating, with some fairly steep lapse rates due to the cold upper low. Moderate bulk wind shear of around 35 to 45 knots will be conducive for organized thunderstorms to continue through the afternoon and into this evening. Shear remains fairly linear, as such the main storm mode is expected to be multicellular, though an isolated supercell is possible early on in the afternoon. Dry mid-levels will help contribute to hail growth this afternoon, which could reach up to 2 cm in size.

Elsewhere, a very slowly moving frontal boundary off the Atlantic coast of Nova Scotia has been triggering some isolated thundershowers overnight, aided by a moderate 500 mb jet. Later this afternoon, as the left exit to this jet reaches Newfoundland, a few isolated thundershowers may trigger over southwestern portions of the province and progress northeast later this afternoon. Modest MLCAPE values of 500 to 1000 J/kg should be enough for some of these thundershowers to develop, but weaker bulk shears will keep anything from getting too organized. As such, the main hazards with these storms will be locally heavy downpours.

Thunderstorm Outlook for Today

Thunderstorm Outlook for Tonight

Thunderstorm Outlook for Tomorrow

Forecaster: Copp

Convective Outlook Valid for Today , Tonight and Tomorrow

Regional Impacts

Today: risk of a thundershower near the ATL coast of NS as well as portions of NF. Scattered afternoon thunderstorms likely for southeastern LAB giving some gusty winds and possibly small hail. Slight risk of a thunderstorm this afternoon in NB.

 

Thursday: likely numerous afternoon and evening thunderstorms for a good portion of NB giving strong winds, hail and torrential rainfall. Isolated thunderstorms possible for western LAB, the interior of NF and some regions of the MRTMs.

 

Convective Discussion

Frontal trough crossing eastern NS and NL produced a couple isolated cells early this morning but have since weakened. Given the history there remains a chance of an elevated thundershower or 2 as the trough continues moving eastward. Another weak trough-like feature will likely spark some scattered thunderstorms across southeastern LAB this afternoon that could give some gusty winds, small hail and brief heavy downpours. The other area that could see some lightning is in NB, but I am having trouble finding a trigger. We have the heat and humidity, with good shear but lacking that trigger and instability. So just the slightest risk of a thunderstorm is expected.

 

Thursday could be active on the desk. A colleague once told me “I never met an upper low I could trust”. And that is what we will have approaching the region from Quebec in the afternoon and evening. All the ingredients will be in play so expect some strong to severe thunderstorms for most of NB. The activity could spill well into the evening hours.

 

Lastly there once again is no D3 prog sent this morning, but as that upper low/trough continues to dive E/Seward there could be strong to possibly severe thunderstorms for some regions of the MRTMs on Friday. Today’s potential outcome upstream in ON and QC should give an idea of what to expect in NB tomorrow. And what happens tomorrow will give a feel for what to anticipate on Friday. It’s the gift that keeps on giving…

 

Thunderstorm Outlook for Today

 

Thunderstorm Outlook for Tonight

 

Thunderstorm Outlook for Tomorrow

 

Jeremy

Convective Outlook Valid for Today , Tonight and Tomorrow

Regional Impacts

Today: scattered thunderstorms for western Labrador giving some gusty winds. Isolated thunderstorms for parts of the Maritimes giving torrential rainfall and gusty winds.

 

Tonight: risk of a thunderstorm for portions of Labrador and the Maritimes. Mainly heavy rainfall possible in the Maritimes.

 

Wednesday: an afternoon risk of thunderstorms for southeastern Labrador. New Brunswick and western PEI.

 

Convective Discussion

An elongated trough of low pressure stretching from LAB and NE will progress slowly eastward today giving some scattered thunderstorms for western LAB this afternoon. Some gusty winds to about 70 km/h seem to be the main threat in the stronger cells. The dynamics are slightly weaker as we head south to NB, but the Pwats increase so locally heavy rainfall, along with some decent wind gusts, are the main concern. Instability is relatively weak, so I don’t expect much of a hail threat anywhere today. Will have to see if we get some elevated convection fire up west of NS later this afternoon that could give some hefty downpours for some counties this evening. There has been some history of lightning but currently there is a lull. We shall see…

 

That same trough will continue tracking eastward tonight and into Wednesday giving the risk of a thunderstorm to a good chunk of the region. It will be weakening so the risk is marginal at this time.

 

There is no prog sent for D3 but based on current guidance, there could be some strong, possibly severe, thunderstorms across parts of NB. I just don’t have the confidence to draw a threat area this far in advance.

 

Thunderstorm Outlook for Today

 

Thunderstorm Outlook for Tonight

 

Thunderstorm Outlook for Tomorrow

 

Jeremy

Convective Outlook Valid for Today, Tonight and Tomorrow

Regional Impacts

Today: Organized thunderstorms today across the SErn marine district, approaching the Nfld coastline early this afternoon. Lightning is the main hazard. An isolated cell or 2 may also pop up this evening in western Labrador and the Edmundston valley area of NWrn NB. A quick 5-10mm of rain could fall.

Tonight: No thunderstorms forecast in ATL Canada.

Tuesday: Late-day thunderstorms are forecast, with the progression of a destabilizing trof out of the Great Lakes region of Ontario. The timing of this trof is quite slow. The main hazards would be gusty winds ahead of the system and pockets of moderate rain. Rainfall rates are forecast to exceed 40 mm/h in the tri-counties area of NS *if* the system develops as models suggest.

Wednesday: Atmospheric conditions remain unstable, so afternoon storms are possible across Labrador, NB, NS, and portions of PEI with daytime heating, and relatively high humidity.

Convective Discussion

The first forcing at play is pulling out of the eastern marine region this afternoon. Mid-levels behind this feature on this morning’s soundings are prohibitively dry. However, Caribou is expected to moisten at 700 throughout the afternoon and as such could produce enough lift late day to spark a cell or 2. They will remain non-severe in nature. The regime tomorrow is somewhat more complex. Another trof is cutting across the Great Lakes and will de-stabilize the now moistened (and near heat warning) Maritimes environment. This will lead to both a wind gust hazard and moderate rainfall hazard on Day 2. If the total energy can be realized before sunset, some cells could approach severe limits. This is being closely monitored as many factors have to line up just right. The Day 3 outlook remains unstable across much of the Maritimes and Labrador with humid sfc conditions and cool air aloft from a developing upper low. This will create pockets of moderate shear with organized convection developing in the afternoon.

Thunderstorm Outlook for Today

Thunderstorm Outlook for Tonight

Thunderstorm Outlook for Canada Day

Thunderstorm Outlook for Wednesday

Forecaster: Tirone.