Convective Outlook Valid for Today, Tonight and Tomorrow

Regional Impacts

Today

LAB: chance of isolated thundershowers over eastern sections giving brief strong wind gusts.

NB: chance of embedded thunderstorms late evening over western sections.

NS/PEI/NL: None

Tonight

NS/NB/PEI: chance of embedded thunderstorms giving heavy rainfall and strong wind gusts.

Tomorrow

NS/NL/LAB: chance of embedded thunderstorms giving heavy rainfall and strong wind gusts.

NB/PEI: None

Convective Discussion

The stalled upper low over Labrador over the last few days is finally starting to track northward and weaken today. There is a weak shortwave currently over central Labrador, moving towards the east, and this is the trigger for thundershowers today. There is potential effective shear of 30-40kt and MLCAPE of 250J/kg, but with low moisture, some cells may organize and provide brief strong wind gusts.

While a ridge dominates the Maritimes and Newfoundland during the day, a low pressure system currently over the Great Lakes will deepen as it tracks towards the Maritimes tonight. Rain ahead with the warm front should reach New Brunswick this evening, while convective showers with the cold front will move across the Gulf of Maine and towards western New Brunswick and Nova Scotia close to midnight. This system is quite active this morning along the warm front, aided by strong dynamical forcing. Overall dynamics and thermodynamics are expected to be reduced as the system reaches the Maritimes. However, there is an increasing 60kt 850mb LLJ tonight ahead of the cold front in Nova Scotia and the southern Maritime waters. This along with possible mid-level cooling aloft may help embedded thunderstorms persist as the front continues eastward overnight, reaching eastern Nova Scotia by mid-morning. Regardless if lightning does persists, strong southerly winds and increasing precipitable water (40-50 mm) will allow for heavy rainfall rates and strong wind gusts with the frontal passage.

For tomorrow, the low centre is expected move from northern New Brunswick towards the northeast, reaching Anticosti by tomorrow evening. The cold front continues to advance, reaching Newfoundland by mid-morning. Embedded thunderstorms are still possible with heavy rain across southern Newfoundland.

Thunderstorm Outlook for Today

Thunderstorm Outlook for Tonight

Thunderstorm Outlook for Tomorrow

Convective Outlook Valid for Today, Tonight and Tomorrow

Regional Impacts

Today

Nfld: Chance of scattered non-severe thunderstorms near St. Anthony, and the Avalon.

Labrador: chance of isolated thundershowers in area marked in grey.

Tonight

No thunderstorms forecast in Atlantic Canada.

Tomorrow

Labrador: chance of isolated non-severe thundershowers over eastern sections.

Western Nova Scotia/Gulf of Maine: chance of scattered embedded thunderstorms along an advancing front very late in the day (near midnight into Sunday).

Convective Discussion

There is now dry air in place across the Maritime provinces. This will inhibit any organized convection today. Cu fields are expected to develop by noon, but will struggle to lift past even 700mb. NB is observing sfc dewpoints of just 8 this morning. A thermal ridge is located off to the west over New England.

Nfld is a bit of a different story synoptically. The remnants of a front is still effecting the Avalon and Grand Banks with a thunderstorm chance. And another hang-back trof is acting as a second trigger across southern Labrador and over the tip of the Northern Peninsula. These storms are not expected to reach warning criteria or approach severe limits today.

Weekend Setup: Day 2 brings in a more substantial organized TS risk very late in the day/overnight approaching the Maritimes from the west. Rainfall amounts look to be 25-40mm at this point for some areas of the Maritimes. The frontal passage is overnight Saturday into Sunday morning. This prog is only valid from the noon to midnight time period. Development is shown as grey in the Gulf of Maine.

Thunderstorm Outlook for Today

Thunderstorm Outlook for Tonight

Thunderstorm Outlook for Tomorrow

Forecaster: Tirone. 3:18:01 Jul 17 2026

60   FPCN11 CWHX 171354 FORECASTS FOR NOVA SCOTIA ISSUED   13:54:57 Jul 17 2

Convective Outlook Valid for Today, Tonight and Tomorrow

Regional Impacts

Today

NB/NS/PEI/NL: Risk of thunderstorms giving brief strong winds gusts, small hail and locally heavy downpours. Risk of higher gusts for southwestern New Brunswick and western Nova Scotia this evening.

Lab: Slight risk of a thundershower giving small hail.

Tonight

NL: Slight risk of a thundershower.

NB/PEI/NS/LAB: None

Tomorrow

None

Convective Discussion

An upper low over Labrador will remain stationary today while a quick moving shortwave trough will move from Quebec towards central Maine then southern New Brunswick and Nova Scotia late this afternoon and towards southern Newfoundland by the evening. There is the possibility of pop-up convection ahead of the trough this afternoon where much of the Maritimes is clear this morning, allowing convective temperatures to be reached, especially across PEI, eastern Nova Scotia and southwestern Newfoundland once clouds clear early this afternoon. With relatively dry dew points over the Maritimes under a westerly flow, precipitable water of 15 to 20 mm and relatively weak CAPE (500J/kg), thunderstorms that develop are expected to be non-severe.  However, with the trough, dynamics are most favoured in the exit region of a strong 250mb jet moving into southwestern New Brunswick and western Nova Scotia. This area may also see a slight increase in precipitable water and CAPE values in this area may exceed 750 J/kg and effective shear increasing to 50 kts based off Maniwaki and Gray 12Z soundings. Organization is possible with the main threats being strong wind gusts and small hail if a line develops. The risk of more elevated convection will continue tonight into Newfoundland. Under the low over Labrador, showers are expected with the risk of convection east of the low. CAPE is quite low but with very cold air aloft, small hail is possible.

For tomorrow, the upper low will slowly make its way eastward by the evening. Other than continued scattered showers with the upper low, the risk of convection at this time is low.

Thunderstorm Outlook for Today

Thunderstorm Outlook for Tonight

Thunderstorm Outlook for Tomorrow

Convective Outlook Valid for Today, Tonight and Tomorrow

Regional Impacts

Today:

NB/NS/PEI/NL: Risk of thunderstorms giving strong wind gusts, small hail and brief heavy downpours.

LAB: Risk of thunderstorms giving small hail.

Tomorrow

NB/NS/PEI/NL: Risk of a thundershower giving strong winds gusts and small hail.

LAB: Risk of a thundershower giving small hail.

Convective Discussion

An upper low over Labrador will become stacked today while a cold front continues across southeastern Labrador, Newfoundland and exits south of Nova Scotia this morning. While high level smoke prevented much of the anticipated convection yesterday, convection has been able to fire across southeastern New Brunswick, PEI and Newfoundland this morning where the smoke has cleared. Elevated convection across Newfoundland and the Maritimes marine waters south of Nova Scotia is also on the go this morning with the help of a 45kt low to mid level jet and a favourable upper jet. With dewpoints in the mid to high teens and precipitable water of 30-35, there is the risk of heavy downpours and possible small hail.  East of the low, sufficient lift will aid in thunderstorms continuing across eastern Newfoundland and southeastern Labrador.  Mixed CAPE of upwards of 750 J/kg and effective shear of 20 to 30 kt will allow convection to sustain.

Daytime heating with clearing skies and cooler air aloft will aid in the potential for convection continuing across eastern Nova Scotia, the southern Gulf of St. Lawrence and into central Newfoundland by the afternoon. Mixed CAPE may reach upwards of 1500 J/kg and with effective shear of 40 kt, cells that develop may organize into lines, with a small risk a supercell with sufficient low level helicity this morning. The drier air aloft entering from New Brunswick could lead to brief strong wind gusts in pop up convection across northern New Brunswick later this afternoon.

For tomorrow, a short wave trough from Quebec will track into New Brunswick and across the Maritimes in the afternoon. With relatively dry dew points still in the area under a west-northwest flow and reduced CAPE (500J/kg), the main threats will whatever develops will be brief strong wind gusts and small hail.

Thunderstorm Outlook for Today

Thunderstorm Outlook for Tonight

Thunderstorm Outlook for Tomorrow

Convective Outlook Valid for Today , Tonight and Tomorrow

Today’s Regional Impacts

New Brunswick… tornadic thunderstorms are possible this afternoon. These storms are forecast to form into squall lines by this evening with a straight line wind gust risk. Moderate hail is also possible.

NS/PEI/Iles-de-la-Madeleine/Nfld… thunderstorms are possible late this evening and tonight as the NB convection drifts S and SE across the rest of the Maritimes and the Gulf of St. Lawrence.

Labrador… scattered thunderstorms are possible along an advancing trof with small hail and gusty winds, similar to yesterday.

Convective Discussion

Today is a dynamic day across NB and parts of Quebec and Maine. Over northern and central parts of New Brunswick, effective shear values are topping 40kts, with MLCAPE values near 1750J/kg this afternoon. In the lowest levels, helicity values are also nearing 200. The morning shape of Caribou’s hodograph is a bit messy, but averaged out it has the correct curvature. Dewpoints are already at 18, giving Pwats near 45 in this airmass.

The trigger and its orientation are what become important later today. The advancing trof looks to be timed to pass through at the period of maximum daytime heating. As well, the orientation of the jet streak is NW to SE, and will drive at first discrete cells to then crowd each other and form squall lines. This means a tornadic risk initially in the supercell environment, and then a significant straight line wind gust threat throughout the evening hours. Squall watches/warnings may also be required for adjacent marine regions, ahead of this feature. Sig tor, hailcast, and other indices are flagging the same hazards that were identified on this morning’s Miller workup. Of additional note is the CIN (minor) at play as well: upper level forest fire smoke, and prevailing morning cloud cover.

A severe thunderstorm watch has been issued. An additional 18z ballon has been requested at Gagetown to aid in forecasting/alert upgrading.

Thunderstorm Outlook for Today

Thunderstorm Outlook for Tonight

Thunderstorm Outlook for Tomorrow

Forecaster: Tirone.