Convective Outlook Valid for Today, Tonight and Tomorrow

Regional Impacts

Today

NL: Slight chance of a thundershower over eastern regions early this afternoon giving heavy downpours.

NB/NS/PEI/LAB : None

Tonight 

None

Tomorrow

LAB : Risk of a thundershower over western regions in the evening giving small hail  and locally heavy downpours.

NB/NS/PEI/NL : None 

Convective Discussion

A low pressure system exits east of Newfoundland this morning and from the 12Z St. John’s sounding, there is some instability from 850 to 500 mb so a slight risk of an embedded thundershower remains for early afternoon near the low centre where there is expected to be sufficient lift to break the cap. Otherwise, a ridge of high pressure over Hudson Bay will continue southeastward towards Atlantic Canada, limiting convection and ushering a more moderately cooler and drier air mass. Only a few isolated showers are expected in the northerly onshore flow off the Gulf of St. Lawrence this afternoon. A weak trough will affect eastern Labrador tonight but no convection is expected with that feature.

For tomorrow, the ridge progresses further east into the Maritimes. The weak trough will affect eastern Newfoundland, but again not expecting convection with this feature. A weak trough north of the ridge will aid in triggering thunderstorms over western Labrador late in the afternoon and evening. MLCAPE may reach 500 J/kg but 0-6km shear is fairly weak at 10 to 20kt, so only expecting multicell type storms with brief wind gusts, small hail and locally heavy downpours.

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: Risk of thundershowers, possibly near severe into this evening with gusty winds and locally heavy downpours.

NFLD: Risk of thundershowers this afternoon and evening with locally heavy downpours.

LAB: None.

Tonight

NFLD: Chance of an isolated thundershower overnight and early in the morning with locally heavy downpours.

NS/NB/PEI/LAB: None.

Tomorrow

NB/NS/PEI/NFLD/LAB: None.

Convective Discussion

A shortwave is moving into the Gaspe Peninsula this morning and will be the main trigger for convection today across the Maritimes, Gulf of St. Lawrence, and Newfoundland. Scattered showers across northern New Brunswick will continue this afternoon across PEI, reaching northern Nova Scotia by the evening. MLCAPE values out ahead of the system are expected to rise to 500 to 750 J/kg, with the highest SBCAPE potentially reaching 1200 J/kg expected over southeastern NB, PEI, and north and eastern NS. Although there are fairly weak lapse rates with temperatures warmer at 500 mb, there is still appreciable precipitable water in the mid 30s, drier air between 700 and 500 mb, and effective shear of 40 to 50kt. There is a risk of thunderstorms reaching severe limits and a non zero risk of an isolated supercell this afternoon mainly over the aforementioned areas. Surface-based thundershowers may also develop over central Newfoundland this afternoon.

A risk of thundershowers exists overnight with the shortwave as it tracks east of Cape Breton towards eastern Newfoundland by the morning.

For tomorrow, the shortwave is expected to weaken as it moves east of Newfoundland but there may still be a risk of a thundershower in the early afternoon. A ridge of high pressure will set up over the region on Sunday, leading to a quiet couple of days to begin next week.

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 thunderstorms this afternoon and evening with strong wind gusts, small hail, and heavy downpours.

NS/PEI: Risk of thunderstorms this afternoon and evening with strong wind gusts, small hail, and heavy downpours.

NFLD: Risk of thunderstorms across parts of western, central, and northern Newfoundland this afternoon and evening with strong wind gusts, small hail, and heavy downpours.

LAB: Risk of isolated thunderstorms across southern Labrador this afternoon and evening with strong wind gusts, small hail, and heavy downpours.

Tonight

PEI, NS and NFLD.. A chance of thunderstorms giving locally heavy downpours.

Tomorrow..

PEI, NS and NFLD.. A chance of thunderstorms giving locally heavy downpours.

Convective Discussion

An upper-level trough will remain nearly stationary through most of today before gradually progressing across the Atlantic Region on Saturday and Sunday. Ahead of this feature, a warm and moist airmass will remain in place, with deep-layer shear around 40 kt and modest mixed-layer CAPE of 750–1500 J/kg. Upper-level flow will remain largely zonal from the west.

Several active thunderstorm complexes over Gulf waters may aid convective initiation over Cape Breton and Newfoundland later today. Across New Brunswick, initiation may be more subtle, but storms are expected to intensify once again as they approach the Acadian coastline.

Yesterday produced several supercell thunderstorms, including reports of damage and a likely waterspout over the Northumberland Strait. While the airmass is not expected to be quite as unstable today, similar storm modes remain possible. In addition, very high low-level moisture, with dew points near 20°C and precipitable water values approaching 40 mm, will support efficient rainfall production and high rainfall rates across all regions, including Labrador.

Thunderstorms may persist into the overnight period and continue to affect portions of the region. The greatest risk appears to be across Cape Breton and eastern Nova Scotia; however, as has been the case with recent nocturnal convective events, the exact location and extent of overnight activity remain difficult to determine.

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

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