Convective Outlook Valid for Today , Tonight and Tomorrow

Regional Impacts

Labrador… Risk of thunderstorms today and tomorrow, with heavy downpours and some gusty winds possible.

Newfoundland… Risk of thunderstorms across eastern Newfoundland today, with some heavier downpours and frequent lightning possible.

PEI… Slight risk of thunderstorms today.

Nova Scotia…  Slight risk of thunderstorms today, mainly across eastern areas.

New Brunswick… Risk of isolated thunderstorms, mainly over northwestern sections late in the day.

 

Convective Discussion

The region currently remains under a somewhat anomalous pattern characterized by weak blocking. Most of the Maritimes lie between a trough extending from the Great Lakes northward into Labrador and a slow-moving low-pressure system approaching the Avalon Peninsula. This pattern is resulting in generally weak steering flow and a continued focus for convective development across portions of the region.

Across Labrador, conditions are expected to remain much the same as they were yesterday, although vertical motion may be slightly weaker. CAPE values in the 500 to 1000 J/kg range, combined with moderate low-level shear, will continue to support fairly widespread convection through the afternoon and evening. Rainfall rates in the strongest storms will likely reach 15 to 20 mm/h.

The low-pressure system over the marine area south of Newfoundland has transported more moisture into eastern portions of the Maritimes than previously anticipated. This increase in moisture has raised the potential for showers and thunderstorms in areas where low-level convergence is sufficient to overcome existing convective inhibition. However, with the exception of eastern Newfoundland, the shear profile across the region is generally not supportive of severe thunderstorms. As a result, most convection is expected to be relatively weak and disorganized, with only a low risk of severe weather. Nevertheless, locally heavy downpours remain possible where thunderstorms are able to develop.

Over eastern Newfoundland, the combination of stronger forcing associated with the nearby low-pressure system and somewhat more favourable wind profiles will support more organized convection. The most likely scenario remains clusters of thunderstorms capable of producing frequent lightning and locally heavy rainfall, with rainfall rates of 15 to 25 mm/h possible in the strongest cells. Strong downdrafts and hail are not expected to be significant concerns at this time.

Thunderstorm Outlook for Today

Thunderstorm Outlook for Tonight

Thunderstorm Outlook for Tomorrow

 

Mel Lemmon

Convective Outlook Valid for Today , Tonight and Tomorrow

Regional Impacts

Labrador… Risk of thunderstorms with downpours and small hail possible, today and tomorrow.

Newfoundland… Risk of elevated thunderstorms tomorrow with some heavier downpours.

PEI, NS… No Risk of thunderstorms.

New Brunswick… Risk of thunderstorms northwest tomorrow.

Convective Discussion

A surface trough will continue to move across Labrador today shifting slightly farther east tomorrow, with moderate instability developing during the afternoon. CAPE values are forecast to be in the 500 to 1000 J/kg range, while strong low-level winds will provide support for organized convection where thunderstorms are able to develop.

Scattered thunderstorms are expected along and ahead of the trough this afternoon and this evening. Rainfall rates could reach 15 to 20 mm/h, although the progressive nature of the storms should limit the duration of heavy rainfall at any one location.

While severe weather is not anticipated, some storms may become organized into short line segments or a convective complex. Should this occur, locally heavier rain and some gustier winds are possible.

Across eastern Newfoundland, a low-pressure system tracking near the Avalon Peninsula will provide additional lift and support for elevated convection. While surface-based instability is expected to remain limited, elevated thunderstorms may develop within the broader area of precipitation associated with the system. The strongest thunderstorms over eastern Newfoundland will be capable of producing brief periods of heavy rain, with rainfall rates of 15 to 25 mm/h possible.

Thunderstorm Outlook for Today

Thunderstorm Outlook for Tonight

Thunderstorm Outlook for Tomorrow

Mel Lemmon

Convective Outlook Valid for Today , Tonight and Tomorrow

Regional Impacts

Labrador… Risk of thunderstorms with downpours and small hail possible, today and tomorrow.

Newfoundland, PEI, NS… No Risk of thunderstorms.

New Brunswick… Risk of thunderstorms just north of province.

Convective Discussion

A ridge of high pressure over eastern Atlantic Canada will suppress convection across much of the region. Over the next couple of days, this ridge will gradually shift east, allowing an area of low pressure to move slowly across the remainder of the region. There is some potential for deeper convection just ahead of the low and its associated surface trough over Labrador, both today and tomorrow.

For Labrador, surface-based CAPE values between 500 and 1000 J/kg today and tomorrow will provide sufficient instability for thunderstorm development. Today, however, the triggering mechanism will be subtle. By tomorrow, a surface trough will provide a more focused trigger along with slightly higher low-level moisture. As a result, locally heavy downpours and small hail will become somewhat more likely ahead of this feature. Deep-layer shear is moderate, while low-level shear of around 20 knots may be sufficient to organize convection into a line or possibly support training thunderstorms.

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: Risk of thunderstorms near noon and later today over western sections.

Northern NB: Risk of a TCU or very brief isolated thundershower later today.

Offshore and over the Avalon: Embedded convection is ongoing and remains possible today.

Tonight

Thundershower activity is not forecast over land areas tonight.

Tomorrow

Lab: Thunderstorm risk expands further north and east along the shifting frontal boundary.

Coastline of Nova Scotia: Embedded thundershower risk circles around the offshore low and may approach the Atlantic coast late in the day (prog goes until midnight). Not forecasting anything severe at this time.

Convective Discussion

Atlantic Canada finds itself sandwiched between 2 elongated frontal boundaries this weekend. One is offshore and stretches from the Grand Banks to the Carolinas. The second is situated from Ungava Bay back to eastern Lake Superior. It is easy to see the forcings on the 500mb charts, but additionally the cloud field on satellite is quite pronounced this morning. These long wave troughs are the lifting mechanisms for any convection that occurs in the next 24 to 48-hrs. Moisture is ok, but shear is substantially lacking in NB. Labrador is a different story. Shear may actually be too great for the amount of lift available. That being said, if an organized cell can form tomorrow, gusty winds (of 60 to 70 km/h) nearby could be a factor at play. This will be monitored. **Also of note is the forest fire smoke that is still affecting some areas of central Quebec. This could act as CIN that the models are not accounting for.

Thunderstorm Outlook for Today

Thunderstorm Outlook for Tonight

Thunderstorm Outlook for Tomorrow

Forecaster: Tirone.

Convective Outlook Valid for Today , Tonight and Tomorrow

Regional Impacts

Today

Lab: Risk of non-severe thundershowers.

NL: Risk of embedded thundershowers over the Avalon, bringing moderate (to at times potentially heavy) rainfall.

Tonight

Thundershower activity pushes out over the eastern marine domain.

Tomorrow

Lab: Thunderstorms are possible over western sections.

NB: There is a risk of thunderstorms developing in the afternoon over central and northern areas.

Convective Discussion

An elongated frontal boundary continues to affect the eastern parts of Nfld today giving a chance of embedded thundershowers. The potential hazard here is moderate to heavy rainfall in convective burts. Pwats on St. John’s sounding this morning is 39, showing the airmasses’ tropical nature. This forcing will slump over the eastern marine domain tonight, marked in broad grey. There is a secondary forcing across Labrador and the Quebec Lower North Shore that will act as a TCU/CB trigger this afternoon. These storms are not expected to reach severe limits – CAPE is 500-750J/kg, effective shear 15-25kts. Isolated lightning is the main hazard. This trof is the forcing for Day 2 in NB.

Thunderstorm Outlook for Today

Thunderstorm Outlook for Tonight

Thunderstorm Outlook for Tomorrow

Forecaster: Tirone.