Convective Outlook Valid for Today, Tonight and Tomorrow

Regional Impacts

Today:

NL : Risk of a thunderstorm west of the Avalon Peninsula giving strong winds, small hail and locally heavy downpours. Risk of a thunderstorm over the Northern Peninsula giving strong winds, small hail, and locally heavy downpours.

LAB: Risk of a thunderstorm giving strong winds, small hail, and locally heavy downpours over central and eastern regions.

NS/NS/PEI : NIL

Tonight :

None

Tomorrow :

Lab : Risk of an isolated thundershower over the central regions.

NL/NS/NB/PEI : NIL

Convective Discussion

As a ridge continues to build over the Maritimes, a low-pressure system south of Greenland is allowing several jets to align just off the northern shores. Surface analysis shows these jets stacked on top of each other over the north coast, along with some slight convergence area both at the surface and at 850mb. Additionally, with this storm south of Greenland there is multiple embedded short-waves moving in a Northwest-Southeast direction. These features along with dewpoints forecasted to remain near 12°C with temperatures rising to near 25, there is a risk for some thunderstorms that are capable of producing strong winds, hail up to 2cm. There remains once again some model uncertainty between the RDPS and HRDPS. Upon closer inspection of the 00z Soundings and the 12z Stephenville Soundings, the HRDPS has a much better initialization when compared to the RDPS. This is important to note as there are significant differences in thunderstorm potential between the HRDPS and RDPS for regions near the Avalon (with the RDPS being the lesser of the two). All of this being said, over Labrador, there were some early morning lightning strikes that occurred, but the main struggle for today will be fighting off the smoke in the regions. Looking at the observations from Wabush, there have been consistently reports of smoke, which would act as an inhibitor to convection today.

For tonight, convective activity is not expected to occur. This is primarily due to smoke continuing to move into the region and overnight stability setting in.

Tomorrow, there is a chance of thunderstorms developing. These thunderstorms are likely to be terrain-induced near Happy Valley Goose Bay. There will be continued smoke moving in from Quebec, but models currently show smoke clearing out of this region as a slow-moving system over Hudson Bay progresses eastward.

Thunderstorm Outlook for Today

Thunderstorm Outlook for Tonight

Thunderstorm Outlook for Tomorrow

Forecaster: Lambert/Firth

Convective Outlook Valid for Today, Tonight and Tomorrow

Regional Impacts

Today

Lab: Risk of a thundershower over western regions this evening giving locally heavy downpours.

NB/NS/PEI/NL : Nil

Tonight

Lab : Slight chance of an isolated thundershower overnight.

NB/NS/PEI/NL : Nil

Tomorrow

NL : Risk of a thunderstorm near the Avalon Peninsula giving strong winds, small hail and heavy downpours. Risk of a thundershower over the Northern Peninsula.

Lab: Risk of a thundershower giving locally heavy downpours over central and eastern regions.

NB/NS/PEI: Nil

Convective Discussion

As a ridge builds through the Maritimes, 850mb and 700mb Jets orientated relatively north-south will aid in the trigger of some thundershowers over Labrador this evening. Generally, for these thunderstorms values of Mixed Layer CAPE (MLCAPE) will be staying close to the 500-700 J/Kg range with Surface Based CAPE (SBCAPE) being slightly higher nearing the 1,000 J/Kg range. Given these CAPE values along with a relatively weak Effective Shear of around 20Kt any convection that does occur will be isolated in nature and is expected to be short-lived. This is also applicable for the overnight hours into tomorrow morning, generally there is a risk for elevated thundershowers over Labrador, though the forcings in the overnight hours will be weaker hence the area outlined does not have any attributes attached to them.

For tomorrow, the ridge moves further southeast and allows for a higher dewpoints and stronger jets to interact with the land-sea boundaries from Trinity Bay and Placentia Bay, which could give rise to more intense thunderstorms in eastern Newfoundland. Currently there is some discrepancy between the Regional and High-Res model guidance for this event. The High-Res currently has higher dewpoints extending further into the atmosphere along with a slight easterly flow, meanwhile the Regional has slightly drier layer with a complete westerly flow throughout the atmosphere column. This discrepancy is enough to not indicate a risk for tornadoes, but is possible with a High-Res solution. With the High-res solution the main region of concern would be from Clarenville to CBS and extending down to Argentia. Meanwhile up in Labrador and the Northern Peninsula, jet streaks still remain the active triggering mechanism though with slightly lower CAPE values the risk for a severe thunderstorm is low.

Thunderstorm Outlook for Today

Thunderstorm Outlook for Tonight

Thunderstorm Outlook for Tomorrow

Forecaster: Lambert/McArthur

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