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

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Forecaster: Tirone.

Convective Outlook Valid for Today , Tonight and Tomorrow

Today’s Regional Impacts

Labrador… thunderstorms are possible with small hail and gusty winds.

Northeastern NB/Bay of Chaleur area … isolated non-severe thundershower is possible late this afternoon and early this evening.

Convective Discussion

Today is a calm day with moderate humidity and hazy skies across the Maritimes. Sfc dew points are in the mid teens, but a capping ridge is in place. Yarmouth 12z sounding shows very dry air between 850 and 500. Without a trigger, thunderstorms are not forecast for PEI, NS, central/southern NB, and Nfld. Labrador will see thunderstorms develop due to an area of low pressure that is advancing east out of northern Quebec. Goose Bay 12z balloon shows Pwats near 26 this morning. Forest fire smoke is the catch though -- that may hinder some development.

Tomorrow across the Maritimes is a much different story. The ingredients for severe weather are likely to come together at the peak of daytime heating. This could lead to elevated hail, wind, and rainfall rate risks. Additionally, some indices are showing a non-zero tornadic risk in parts of NB. A properly aligned low level jet and high CAPE values (for this time of year) will be closely monitored tomorrow. An area marked in yellow has been used in the day 2 outlook to depict the heightened weather risk for Tuesday afternoon and evening. Some of these storms may make it into the Northumberland Strait area and Bay of Fundy by late evening.

Thunderstorm Outlook for Today

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Forecaster: Tirone.

Convective Outlook Valid for Today , Tonight and Tomorrow

Regional Impacts

Labrador… Isolated thunderstorms with some strong wind gusts possible.

Newfoundland… probability of thunderstorms very low.

PEI and NB… probability of thunderstorms very low.

NS… Slight chance of thunderstorms over eastern areas.

Convective Discussion

Most areas will experience a couple of days of relatively quiet convective weather, with the exception of Labrador, where a moderately unstable airmass will persist through today and Monday. CAPE values are expected to remain generally between 500 and 1000 J/kg, while freezing levels remain relatively low, between 8,000 and 9,000 ft. As a result, isolated thunderstorms may produce gusty winds and small hail. However, with weak wind shear and a lack of significant surface forcing, organized convection is not expected.

Looking ahead to Tuesday, there is increasing potential for a more favorable severe weather environment to develop. Forecast guidance suggests stronger upper-level dynamics, increasing wind shear, and additional low-level moisture, all of which could support stronger thunderstorm development. While model uncertainty remains relatively high at this lead time, there is some agreement among guidance that a severe weather episode may be possible. Forecast confidence should improve over the next 24 hours, allowing for a better assessment of timing, storm mode, and overall severe weather potential.

Thunderstorm Outlook for Today

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Mel Lemmon

Convective Outlook Valid for Today , Tonight and Tomorrow

Regional Impacts

Labrador… Risk of thunderstorms with gusty winds and small hail.

NS,NS and PEI… Slight Risk of thunderstorms with locally heavy downpours.

NFLD… Low chance of thunderstorms with downpours possible.

Convective Discussion

A somewhat drier airmass has moved into much of the Atlantic Region today. Instability remains marginal, with CAPE values generally between 500 and 1000 J/kg. Deep-layer shear is relatively weak, limiting the potential for organized convection. Nevertheless, ascent associated with the upper trough moving across the region should support the development of scattered showers and thunderstorms this afternoon.

Across the Maritimes, precipitable water values remain somewhat elevated, generally between 25 and 30 mm. While storm organization is not expected, any thunderstorms that develop may produce locally heavy rainfall rates due to the enhanced moisture content of the airmass.

Over Labrador, drier mid-level air behind the trough may enhance downdraft potential through evaporative cooling. Although severe wind gusts are not anticipated, the strongest cells could produce gusts exceeding 50 km/h. In addition, freezing levels below 9,000 ft will support the potential for small hail in the more intense thunderstorms.

Thunderstorm Outlook for Today

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Mel Lemmon

Convective Outlook Valid for Today , Tonight and Tomorrow

Regional Impacts

Newfoundland… low chance of thunderstorms overnight and tomorrow.

Labrador... Chance of a thunderstorm, today and tomorrow. Small hail possible.

NS… Some thunderstorms with locally heavy rainfall amounts today. Risk of a thunderstorm tomorrow.

PEI and NB... Scattered thunderstorms with some locally heavy downpours today and tomorrow.

 

Convective Discussion

The higher atmospheric moisture content currently over the Maritimes will shift eastward today, reaching eastern Newfoundland overnight and into tomorrow morning. Across Nova Scotia, precipitable water values exceeding 40 mm, combined with somewhat favourable upper-level dynamics, will support the potential for heavy rainfall. Rainfall rates exceeding 25 mm per hour have already been observed, and there remains the potential for these rates to continue or redevelop over eastern Nova Scotia. With moderate low-level shear and CAPE values of 500–1000 J/kg, some organized convective lines or clusters may develop.

A somewhat drier airmass will move in behind this moisture plume on Friday. As a result, rainfall rates are expected to be lower than those observed today. However, CAPE values are forecast to remain moderate, supporting scattered thunderstorm development. Deep-layer and low-level shear are expected to remain relatively weak, limiting storm organization. Consequently, organized convection is not anticipated.

Thunderstorm Outlook for Today

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Mel Lemmon