Convective Outlook Valid for Today, Tonight and Tomorrow

Regional Impacts

Today

NB: Risk of severe thunderstorms in the afternoon and into the evening capable of producing very strong wind gusts, dime to nickel sized hail, and heavy downpours.

NS/PEI: Chance of a thunderstorm in the evening capable of producing strong wind gusts, small hail, and heavy downpours.

NFLD: Chance of some isolated thundershowers in the early afternoon over central and eastern Newfoundland which could produce some heavy downpours.

LAB: Risk of an isolated thunderstorm reaching southwestern Labrador this evening giving small hail, strong winds and heavy downpours.

Tonight:

NB/PEI/NS: Risk of elevated thunderstorms giving heavy downpours.

Tomorrow

NB/PEI/NS/NL: Risk of near severe thunderstorms in the afternoon and into the evening capable of producing strong wind gusts, small hail hail, and heavy downpours.

LAB: Risk of isolated thunderstorms giving brief wind gusts, small hail and heavy downpours.

Convective Discussion

The active weather continues today under a hot and humid airmass. Watches and warnings were on the go early this morning from the shortwave moving across the Gulf of St. Lawrence into Newfoundland extending southwest into Nova Scotia aided by a strong upper level jet. Heavy downpours (PWTAS into the 50s) and intense lightning have been observed with the storms and they will continue southeastward across eastern Newfoundland and over the southern marine waters this afternoon.

Another area of active weather is expected for New Brunswick today. With ample energy already in place (dew points this morning 19 to 23C) giving MLCAPE possibly reaching 2000 J/kg, the trigger will be an upper jet as is crosses central Quebec this morning and into northern New Brunswick along with daytime convective temperatures expected to be reached under clear skies this morning. The 12Z Caribou sounding is not available, but looking further upstream at the Maniwaki and Chibougamau soundings, they are indicating decent 0-6km shear of 35 to 45kt and PW of 43mm. With effective shear increasing by the afternoon to near 50 kt, there is the risk for bowlines or potential supercells given some low level spin available. Freezing levels are high but dime to nickel sized hail, strong winds and very high rainfall rates are likely.

Thunderstorms may also reach into extreme southwestern Labrador today with the unstable airmass.

For tonight, thunderstorms should begin to lessen across New Brunswick with the sun setting but there could be some lingering elevated convection past midnight across the Gulf of St. Lawrence with the upper jet still in place. There is another shortwave expected to affect southern Quebec into Maine this evening and any convection may continue overnight into western Nova Scotia with the help of the upper jet over the area. Lightning and heavy downpours will be the main risks.

For tomorrow, an upper low slowly tracks eastward across central Labrador while a shortwave trough moves into Newfoundland. Widespread showers are expected to trigger across central to southern Labrador by the early afternoon, while instability, sea breeze convergence and continuing heat and humidity across the Maritimes will aid in thunderstorm development. MLCAPE could exceed 1500J/kg , and shear remains high in the morning near 40-50kt but will diminish some by the afternoon across New Brunswick. Regardless, heavy rain, small hail and strong wind gusts will be the main threats for New Brunswick, PEI and central to eastern Nova Scotia and Newfoundland.

Thunderstorm Outlook for Today

Thunderstorm Outlook for Tonight

Thunderstorm Outlook for Tomorrow

Convective Outlook Valid for Today, Tonight and Tomorrow

Regional Impacts

Today

NB: Risk of severe thunderstorms over northern New Brunswick late this evening capable of producing very strong wind gusts, nickel to quarter size hail, heavy downpours, and the risk of a tornado.

NS: Slight chance of an isolated thundershower over southwestern Nova Scotia early this afternoon.

PEI/NFLD/LAB: None.

Tonight

NS/NB/PEI/NFLD: Risk of severe thunderstorms over the Gulf of St. Lawrence overnight capable of producing strong wind gusts, small hail, and heavy downpours.

LAB : None.

Tomorrow

NB: Risk of severe thunderstorms late in the afternoon and into the evening capable of producing very strong wind gusts, nickel to quarter size hail, and heavy downpours.

NS/PEI: Slight chance of a thunderstorm over western areas in the evening capable of producing strong wind gusts, small hail, and heavy downpours.

NFLD: Chance of some isolated thundershowers in the late morning and early afternoon over central and eastern Newfoundland which could produce some heavy downpours.

LAB: None.

 

Convective Discussion…

An active few days are in store for the Maritimes, with a very hot and humid airmass that has settled over the region. Today brings the potential for severe thunderstorms over northern New Brunswick associated with some upper troughing over central Quebec. MLCAPE values over the area of interest are forecast to rise upwards of 1500 to 2000 J/kg due to the humid airmass. Strong dynamic forcing will also be advected into the region later today as the upper troughing approaches, with effective shear values reaching 50 to 55 knots this evening over northern New Brunswick. One of the major limiting factors today will be how quickly the capping inversion can erode over New Brunswick. Without the 12Z Caribou sounding, it is difficult to gauge the current state of the atmosphere over the region, however the 12Z Maniwaki and Chibougamau sounding both indicate a strong cap around 850 mb. Due to this and the timing of the upper trough swinging through, storms are not expected to fire until later this evening. All hazards are in play today due to the strong dynamics and high CAPE values. PWATs are expected to rise into the 40 to 50 range leading to the potential for some torrential rainfall rates of 25 to 50 mm per hour in these storms. Nickel to quarter size hail will also be possible with some fairly strong lapse rates, in addition to some very strong wind gusts in the range of 90 to 110 km/h. A tornado cannot be ruled out either, with the 12Z Sept-Iles sounding indicating some strong curvature in the low levels. Model hodographs also support strong low level curvature over northern New Brunswick this evening. There also exists a very small chance for an isolated thundershower over southwestern Nova Scotia early this afternoon due to a shortwave over the Gulf of Maine, as well as over eastern Labrador with an upper trough over the Labrador Sea. These storms are unlikely to produce any severe hazards.

Tonight, the main risk area from today will move out over the Gulf of St. Lawrence with the upper jet likely to sustain these thunderstorms overnight. Storms will likely become elevated as they cross the gulf, reducing the severe hazard potential, but strong wind gusts, small hail, and heavy downpours are all still possible. Tomorrow, this risk area will diminish in severity as it moves out over the Atlantic ocean, but a second approaching upper jet could spark up another round of severe thunderstorms over New Brunswick late in the day with similar MLCAPE (1500 to 2000 J/kg) and effective shear (50 to 55 knots) expected. The risk however is slightly lower than today, due to a stronger cap expected to be in place and possibly some drier mid-level air. If storms do spark up late in the day however, they will likely become severe. The main hazards tomorrow will be similar to today (very strong wind gusts, nickel to quarter size hail, and heavy downpours), however more linear shear is expected so no tornado risk is being forecast at this time.

 

Thunderstorm Outlook for Today

Thunderstorm Outlook for Tonight

Thunderstorm Outlook for Tomorrow

Forecaster: Copp

Convective Outlook Valid for Today , Tonight and Tomorrow

Regional Impacts

Nova Scotia.. Slight Risk of thunderstorms today giving heavy downpours and strong winds.

New Brunswick.. Slight Risk of thunderstorms today giving heavy downpours and strong winds. Risk of Severe thunderstorms late tomorrow.

PEI… Low risk of thunderstorms.

Newfoundland.. Slight Risk of thunderstorms today giving heavy downpours and strong winds.

Labrador.. Slight Risk of thunderstorms today giving heavy downpours and strong winds.

Convective Discussion

Our generally unsettled air mass will remain unstable today, with CAPE values exceeding 1000 J/kg across much of the Atlantic Provinces. Moderate shear could be a factor in the Maritimes, with a slight chance that some thunderstorms become organized and possibly back-build.

Over Newfoundland, beneath the upper trough, storms are likely to remain fairly stationary, with little shear available for organization. One possible concern is the development of thunderstorms across northern regions, with new storms forming along a potential land-sea boundary. However, under these very low-shear conditions, it is challenging to determine where storm activity will become most dominant. Torrential downpours and strong wind gusts will be possible with these storms.

Tomorrow, we will see the return of much stronger dynamics as the upper-level jet and stronger shear come into play. The biggest issue will be the timing of cap erosion. Should strong cells move into northwestern New Brunswick tomorrow afternoon—likely later in the day—there is a good chance these storms will exhibit significant mid-level rotation. Damaging winds and even tornadic storms cannot be ruled out.

There remains some uncertainty, but Canada Day has the potential to be problematic from late tomorrow into the evening, especially across northwestern New Brunswick.

Thunderstorm Outlook for Today

Thunderstorm Outlook for Tonight

Thunderstorm Outlook for Tomorrow

 

Mel Lemmon

Convective Outlook Valid for Today, Tonight and Tomorrow

Regional Impacts

Today

LAB: Chance of some scattered thundershowers, some may be capable of producing small hail, strong winds, and locally heavy downpours.

NFLD: Chance of scattered thundershowers in the afternoon capable of producing some strong wind gusts, small hail and locally heavy downpours.

NB: Risk of isolated thunderstorms in the afternoon and early evening which may produce strong wind gusts, small hail, and heavy downpours.

NS/PEI: Risk of an isolated thundershower this afternoon in western PEI and Cape Breton.

Tonight

LAB: Some lingering thunderstorms are possible across southeastern Labrador.

Tomorrow

NS/NL:  Risk of scattered thunderstorms in the afternoon and early evening which may produce strong wind gusts, small hail, and heavy downpours.

NB/LAB: Risk of isolated thunderstorms which may produce brief strong wind gusts, small hail and heavy downpours.

Convective Discussion

The environment remains unstable today across much of the Atlantic Provinces as a cold upper trough stretches from Labrador southwestward towards the northern Gulf of St. Lawrence and northern New Brunswick today. Along and east of the trough axis, mainly sunny skies should allow for good daytime heating into this afternoon. One hinderance may be some smoke aloft which is drifting across southern Labrador and into the Gulf from fires in central Quebec. Regardless, with the potential for MLCAPE to reach or exceed 1500J/kg, and increasing effective shear of 20 to 30 kts, as well as low freezing levels, some storms that develop may reach near severe limits. Multicell storms are most likely with small hail, strong wind gusts and heavy downpours possible, especially as storms will not be moving quickly and may train over the same areas. Enhanced lift due to terrain and sea breeze convergence will aid in some pop-up convection developing across central Newfoundland this afternoon. Shear is lower over this area, so heavy downpours and small hail are the main threat with anything that develops. A weak shortwave trough is expected to reach northern New Brunswick and into the Gulf of St. Lawrence but not until later tonight, likely limiting any severe convection to the Gaspe Peninsula, but an isolated risk is possible with this overnight. This upper trough has a history also of cold core funnels which were witnessed in PEI yesterday, and similar conditions may also occur today.

For tomorrow, the troughing continues southeastward with isolated showers across most areas by the afternoon, but the higher threat of thunderstorms shifts to Newfoundland and central to eastern Nova Scotia where precipitable water is increasing. Surface convergence and daytime heating will aid in increasing instability. There is a risk of multicell or a possible isolated supercell along convergence lines in the late afternoon or evening. Over Labrador, the upper forcing diminishes but daytime heating and terrain influences may still allow for pop-up convection in the afternoon but with quite low dew points, brief strong wind gusts are the main threat.

Thunderstorm Outlook for Today

Thunderstorm Outlook for Tonight

Thunderstorm Outlook for Tomorrow

 

Convective Outlook Valid for Today, Tonight and Tomorrow

Regional Impacts

Today

NB: Risk of severe thunderstorms over parts of western and central NB today, capable of producing small hail, strong wind gusts, and torrential downpours.

NS/LAB: Chance of some scattered thundershowers this afternoon capable of producing strong wind gusts and locally heavy downpours.

NFLD: Chance of some isolated thundershowers this afternoon which may produce some locally heavy downpours.

PEI: None.

Tonight

NS/NB/PEI/NFLD/LAB : None.

Tomorrow

NB: Risk of isolated thunderstorms over northern NB in the afternoon which may produce strong wind gusts, small hail, and heavy downpours.

LAB: Chance of some scattered thundershowers in the afternoon, some may be capable of producing small hail, strong winds, and locally heavy downpours over southeastern Labrador.

NFLD: Chance of some isolated thundershowers in the afternoon capable of producing some strong wind gusts and locally heavy downpours.

NS/PEI: None.

Convective Discussion…

An active day has already set up over parts of New Brunswick today and severe thunderstorm watches have been issued. Some thundershowers moved into western New Brunswick early this morning associated with a small shortwave and have already produced some marginally severe rainfall rates. Some brief clearing is expected over western and central New Brunswick early this afternoon which will allow MLCAPE values to rise up to 1000 – 1250 J/kg, providing more than enough instability for storms to continue firing into this evening. Wind shear remains a slight uncertainty however, with effective shear values varying from 10 knots in the northern half of the province to 20 to 30 knots in the southern half. The storms in the northern half of New Brunswick this afternoon are expected to be very slow-moving and short-lived due to the lack of shear, but these storms are still likely to produce some torrential rainfall rates. This risk also exists in the south, but due to the higher shear, more of a multicellular storm mode is expected which could lead to some training thunderstorms. The main hazard in New Brunswick today is the potential for significant rainfall, but small hail and strong wind gusts are also possible.

Elsewhere, a few pop-up thundershowers are possible over Newfoundland and Nova Scotia this afternoon. Although effective shear over Nova Scotia is similar to southern New Brunswick today (20 to 30 kts), limited MLCAPE of 500 to 750 J/kg should keep these storms sub-severe but will still be capable of producing some strong wind gusts and heavy downpours. Shear is much less over Newfoundland, so any storms that fire here this afternoon will likely be short-lived. Parts of southeastern Labrador could see the potential for some marginally severe storms this afternoon associated with a weak surface trough and some weak vorticity advection at 500 mb. MLCAPE and effective shear is forecast to be marginally higher here than in Nova Scotia/Newfoundland, 1000 J/kg and 20 to 30 knots respectively. This could lead to the potential for some strong wind gusts and locally heavy downpours in any storms that fire here today. One of the major limiting factors however are very low dewpoints. Current observations show surface temperatures in the area in the low to mid twenties, with dewpoints of only around 4 to 8 degrees. This will likely lead to storms being very high based, making it difficult for the aforementioned hazards to reach the ground.

Tomorrow, a similar setup is expected across Newfoundland and Labrador but with slightly better shear across the region due to an approaching upper trough. In New Brunswick, effective shear of 25 to 30 knots and slightly higher MLCAPE than today (1250-1500 J/kg) is expected. There remains some uncertainty in New Brunswick however due to the timing of the shortwave moving in, as well as how much mid and low-level moisture will be available. Current guidance indicates that the shortwave won’t reach northern New Brunswick until late evening which keeps the risk of storms initiating fairly low, but the afternoon environment is supportive of some marginally severe hazards if storms do end up developing.

Thunderstorm Outlook for Today

Thunderstorm Outlook for Tonight

Thunderstorm Outlook for Tomorrow

Forecaster: Copp